# BPF-HELPERS - list of eBPF helper functions - man(7) - [phpMan] [_BPF-HELPERS_(7)](https://www.chedong.com/phpMan.php/man/BPF-HELPERS/7/markdown) Miscellaneous Information Manual [_BPF-HELPERS_(7)](https://www.chedong.com/phpMan.php/man/BPF-HELPERS/7/markdown) ## NAME BPF-HELPERS - list of eBPF helper functions ## DESCRIPTION The extended Berkeley Packet Filter (eBPF) subsystem consists in programs written in a pseudo-assembly language, then attached to one of the several kernel hooks and run in reac‐ tion of specific events. This framework differs from the older, "classic" BPF (or "cBPF") in several aspects, one of them being the ability to call special functions (or "helpers") from within a program. These functions are restricted to a white-list of helpers defined in the kernel. These helpers are used by eBPF programs to interact with the system, or with the context in which they work. For instance, they can be used to print debugging messages, to get the time since the system was booted, to interact with eBPF maps, or to manipulate network packets. Since there are several eBPF program types, and that they do not run in the same context, each program type can only call a subset of those helpers. Due to eBPF conventions, a helper can not have more than five arguments. Internally, eBPF programs call directly into the compiled helper functions without requiring any foreign-function interface. As a result, calling helpers introduces no overhead, thus of‐ fering excellent performance. This document is an attempt to list and document the helpers available to eBPF developers. They are sorted by chronological order (the oldest helpers in the kernel at the top). ## HELPERS **void *bpf_map_lookup_elem(struct bpf_map *_**map_**, const void *_**key_**)** **Description** Perform a lookup in _map_ for an entry associated to _key_. **Return **Map value associated to _key_, or **NULL **if no entry was found. **long bpf_map_update_elem(struct bpf_map *_**map_**, const void *_**key_**, const void *_**value_**, u64 _**flags_**)** **Description** Add or update the value of the entry associated to _key_ in _map_ with _value_. _flags_ is one of: **BPF_NOEXIST** The entry for _key_ must not exist in the map. **BPF_EXIST** The entry for _key_ must already exist in the map. **BPF_ANY** No condition on the existence of the entry for _key_. Flag value **BPF_NOEXIST **cannot be used for maps of types **BPF_MAP_TYPE_ARRAY **or **BPF_MAP_TYPE_PERCPU_ARRAY **(all elements always exist), the helper would return an error. **Return **0 on success, or a negative error in case of failure. **long bpf_map_delete_elem(struct bpf_map *_**map_**, const void *_**key_**)** **Description** Delete entry with _key_ from _map_. **Return **0 on success, or a negative error in case of failure. **long bpf_probe_read(void *_**dst_**, u32 _**size_**, const void *_**unsafe_ptr_**)** **Description** For tracing programs, safely attempt to read _size_ bytes from kernel space ad‐ dress _unsafe_ptr_ and store the data in _dst_. Generally, use **bpf_probe_read_user**() or **bpf_probe_read_kernel**() instead. **Return **0 on success, or a negative error in case of failure. ### u64 bpf_ktime_get_ns(void) **Description** Return the time elapsed since system boot, in nanoseconds. Does not include time the system was suspended. See: **clock_gettime**(**CLOCK_MONOTONIC**) **Return **Current _ktime_. **long bpf_trace_printk(const char *_**fmt_**, u32 _**fmt_size_**, ...)** **Description** This helper is a "printk()-like" facility for debugging. It prints a message defined by format _fmt_ (of size _fmt_size_) to file _/sys/kernel/tracing/trace_ from TraceFS, if available. It can take up to three additional **u64 **arguments (as an eBPF helpers, the total number of arguments is limited to five). Each time the helper is called, it appends a line to the trace. Lines are dis‐ carded while _/sys/kernel/tracing/trace_ is open, use _/sys/kernel/trac‐_ _ing/trace_pipe_ to avoid this. The format of the trace is customizable, and the exact output one will get depends on the options set in _/sys/kernel/trac‐_ _ing/trace_options_ (see also the _README_ file under the same directory). However, it usually defaults to something like: telnet-470 [001] .N.. 419421.045894: 0x00000001: In the above: • **telnet **is the name of the current task. • **470 **is the PID of the current task. • **001 **is the CPU number on which the task is running. • In **.N..**, each character refers to a set of options (whether irqs are en‐ abled, scheduling options, whether hard/softirqs are running, level of preempt_disabled respectively). **N **means that **TIF_NEED_RESCHED **and **PRE‐** **EMPT_NEED_RESCHED **are set. • **419421.045894 **is a timestamp. • **0x00000001 **is a fake value used by BPF for the instruction pointer regis‐ ter. • ** **is the message formatted with _fmt_. The conversion specifiers supported by _fmt_ are similar, but more limited than for printk(). They are **%d**, **%i**, **%u**, **%x**, **%ld**, **%li**, **%lu**, **%lx**, **%lld**, **%lli**, **%llu**, **%llx**, **%p**, **%s**. No modifier (size of field, padding with zeroes, etc.) is avail‐ able, and the helper will return **-EINVAL **(but print nothing) if it encounters an unknown specifier. Also, note that **bpf_trace_printk**() is slow, and should only be used for debug‐ ging purposes. For this reason, a notice block (spanning several lines) is printed to kernel logs and states that the helper should not be used "for pro‐ duction use" the first time this helper is used (or more precisely, when **trace_printk**() buffers are allocated). For passing values to user space, perf events should be preferred. **Return **The number of bytes written to the buffer, or a negative error in case of fail‐ ure. ### u32 bpf_get_prandom_u32(void) **Description** Get a pseudo-random number. From a security point of view, this helper uses its own pseudo-random internal state, and cannot be used to infer the seed of other random functions in the kernel. However, it is essential to note that the generator used by the helper is not cryptographically secure. **Return **A random 32-bit unsigned value. ### u32 bpf_get_smp_processor_id(void) **Description** Get the SMP (symmetric multiprocessing) processor id. Note that all programs run with migration disabled, which means that the SMP processor id is stable during all the execution of the program. **Return **The SMP id of the processor running the program. **long bpf_skb_store_bytes(struct sk_buff *_**skb_**, u32 _**offset_**, const void *_**from_**, u32 _**len_**, u64** _flags_**)** **Description** Store _len_ bytes from address _from_ into the packet associated to _skb_, at _offset_. _flags_ are a combination of **BPF_F_RECOMPUTE_CSUM **(automatically recompute the checksum for the packet after storing the bytes) and **BPF_F_INVALIDATE_HASH **(set _skb_**->hash**, _skb_**->swhash **and _skb_**->l4hash **to 0). A call to this helper is susceptible to change the underlying packet buffer. Therefore, at load time, all checks on pointers previously done by the verifier are invalidated and must be performed again, if the helper is used in combina‐ tion with direct packet access. **Return **0 on success, or a negative error in case of failure. **long bpf_l3_csum_replace(struct sk_buff *_**skb_**, u32 _**offset_**, u64 _**from_**, u64 _**to_**, u64 _**size_**)** **Description** Recompute the layer 3 (e.g. IP) checksum for the packet associated to _skb_. Com‐ putation is incremental, so the helper must know the former value of the header field that was modified (_from_), the new value of this field (_to_), and the num‐ ber of bytes (2 or 4) for this field, stored in _size_. Alternatively, it is possible to store the difference between the previous and the new values of the header field in _to_, by setting _from_ and _size_ to 0. For both methods, _offset_ in‐ dicates the location of the IP checksum within the packet. This helper works in combination with **bpf_csum_diff**(), which does not update the checksum in-place, but offers more flexibility and can handle sizes larger than 2 or 4 for the checksum to update. A call to this helper is susceptible to change the underlying packet buffer. Therefore, at load time, all checks on pointers previously done by the verifier are invalidated and must be performed again, if the helper is used in combina‐ tion with direct packet access. **Return **0 on success, or a negative error in case of failure. **long bpf_l4_csum_replace(struct sk_buff *_**skb_**, u32 _**offset_**, u64 _**from_**, u64 _**to_**, u64 _**flags_**)** **Description** Recompute the layer 4 (e.g. TCP, UDP or ICMP) checksum for the packet associ‐ ated to _skb_. Computation is incremental, so the helper must know the former value of the header field that was modified (_from_), the new value of this field (_to_), and the number of bytes (2 or 4) for this field, stored on the lowest four bits of _flags_. Alternatively, it is possible to store the difference be‐ tween the previous and the new values of the header field in _to_, by setting _from_ and the four lowest bits of _flags_ to 0. For both methods, _offset_ indicates the location of the IP checksum within the packet. In addition to the size of the field, _flags_ can be added (bitwise OR) actual flags. With **BPF_F_MARK_MAN‐** **GLED_0**, a null checksum is left untouched (unless **BPF_F_MARK_ENFORCE **is added as well), and for updates resulting in a null checksum the value is set to **CSUM_MANGLED_0 **instead. Flag **BPF_F_PSEUDO_HDR **indicates the checksum is to be computed against a pseudo-header. This helper works in combination with **bpf_csum_diff**(), which does not update the checksum in-place, but offers more flexibility and can handle sizes larger than 2 or 4 for the checksum to update. A call to this helper is susceptible to change the underlying packet buffer. Therefore, at load time, all checks on pointers previously done by the verifier are invalidated and must be performed again, if the helper is used in combina‐ tion with direct packet access. **Return **0 on success, or a negative error in case of failure. **long bpf_tail_call(void *_**ctx_**, struct bpf_map *_**prog_array_map_**, u32 _**index_**)** **Description** This special helper is used to trigger a "tail call", or in other words, to jump into another eBPF program. The same stack frame is used (but values on stack and in registers for the caller are not accessible to the callee). This mechanism allows for program chaining, either for raising the maximum number of available eBPF instructions, or to execute given programs in conditional blocks. For security reasons, there is an upper limit to the number of succes‐ sive tail calls that can be performed. Upon call of this helper, the program attempts to jump into a program refer‐ enced at index _index_ in _prog_array_map_, a special map of type **BPF_MAP_TYPE_PROG_ARRAY**, and passes _ctx_, a pointer to the context. If the call succeeds, the kernel immediately runs the first instruction of the new program. This is not a function call, and it never returns to the previous program. If the call fails, then the helper has no effect, and the caller con‐ tinues to run its subsequent instructions. A call can fail if the destination program for the jump does not exist (i.e. _index_ is superior to the number of entries in _prog_array_map_), or if the maximum number of tail calls has been reached for this chain of programs. This limit is defined in the kernel by the macro **MAX_TAIL_CALL_CNT **(not accessible to user space), which is currently set to 33. **Return **0 on success, or a negative error in case of failure. **long bpf_clone_redirect(struct sk_buff *_**skb_**, u32 _**ifindex_**, u64 _**flags_**)** **Description** Clone and redirect the packet associated to _skb_ to another net device of index _ifindex_. Both ingress and egress interfaces can be used for redirection. The **BPF_F_INGRESS **value in _flags_ is used to make the distinction (ingress path is selected if the flag is present, egress path otherwise). This is the only flag supported for now. In comparison with **bpf_redirect**() helper, **bpf_clone_redirect**() has the associ‐ ated cost of duplicating the packet buffer, but this can be executed out of the eBPF program. Conversely, **bpf_redirect**() is more efficient, but it is handled through an action code where the redirection happens only after the eBPF pro‐ gram has returned. A call to this helper is susceptible to change the underlying packet buffer. Therefore, at load time, all checks on pointers previously done by the verifier are invalidated and must be performed again, if the helper is used in combina‐ tion with direct packet access. **Return **0 on success, or a negative error in case of failure. Positive error indicates a potential drop or congestion in the target device. The particular positive error codes are not defined. ### u64 bpf_get_current_pid_tgid(void) **Description** Get the current pid and tgid. **Return **A 64-bit integer containing the current tgid and pid, and created as such: _cur‐_ _rent_task_**->tgid << 32 | _**current_task_**->pid**. ### u64 bpf_get_current_uid_gid(void) **Description** Get the current uid and gid. **Return **A 64-bit integer containing the current GID and UID, and created as such: _cur‐_ _rent_gid_ **<< 32 | _**current_uid_. **long bpf_get_current_comm(void *_**buf_**, u32 _**size_of_buf_**)** **Description** Copy the **comm **attribute of the current task into _buf_ of _size_of_buf_. The **comm** attribute contains the name of the executable (excluding the path) for the cur‐ rent task. The _size_of_buf_ must be strictly positive. On success, the helper makes sure that the _buf_ is NUL-terminated. On failure, it is filled with ze‐ roes. **Return **0 on success, or a negative error in case of failure. **u32 bpf_get_cgroup_classid(struct sk_buff *_**skb_**)** **Description** Retrieve the classid for the current task, i.e. for the net_cls cgroup to which _skb_ belongs. This helper can be used on TC egress path, but not on ingress. The net_cls cgroup provides an interface to tag network packets based on a user-provided identifier for all traffic coming from the tasks belonging to the related cgroup. See also the related kernel documentation, available from the Linux sources in file _Documentation/admin-guide/cgroup-v1/net_cls.rst_. The Linux kernel has two versions for cgroups: there are cgroups v1 and cgroups v2. Both are available to users, who can use a mixture of them, but note that the net_cls cgroup is for cgroup v1 only. This makes it incompatible with BPF programs run on cgroups, which is a cgroup-v2-only feature (a socket can only hold data for one version of cgroups at a time). This helper is only available is the kernel was compiled with the **CON‐** **FIG_CGROUP_NET_CLASSID **configuration option set to "**y**" or to "**m**". **Return **The classid, or 0 for the default unconfigured classid. **long bpf_skb_vlan_push(struct sk_buff *_**skb_**, __be16 _**vlan_proto_**, u16 _**vlan_tci_**)** **Description** Push a _vlan_tci_ (VLAN tag control information) of protocol _vlan_proto_ to the packet associated to _skb_, then update the checksum. Note that if _vlan_proto_ is different from **ETH_P_8021Q **and **ETH_P_8021AD**, it is considered to be **ETH_P_8021Q**. A call to this helper is susceptible to change the underlying packet buffer. Therefore, at load time, all checks on pointers previously done by the verifier are invalidated and must be performed again, if the helper is used in combina‐ tion with direct packet access. **Return **0 on success, or a negative error in case of failure. **long bpf_skb_vlan_pop(struct sk_buff *_**skb_**)** **Description** Pop a VLAN header from the packet associated to _skb_. A call to this helper is susceptible to change the underlying packet buffer. Therefore, at load time, all checks on pointers previously done by the verifier are invalidated and must be performed again, if the helper is used in combina‐ tion with direct packet access. **Return **0 on success, or a negative error in case of failure. **long bpf_skb_get_tunnel_key(struct sk_buff *_**skb_**, struct bpf_tunnel_key *_**key_**, u32 _**size_**, u64** _flags_**)** **Description** Get tunnel metadata. This helper takes a pointer _key_ to an empty **struct** **bpf_tunnel_key **of **size**, that will be filled with tunnel metadata for the packet associated to _skb_. The _flags_ can be set to **BPF_F_TUNINFO_IPV6**, which indicates that the tunnel is based on IPv6 protocol instead of IPv4. The **struct bpf_tunnel_key **is an object that generalizes the principal parame‐ ters used by various tunneling protocols into a single struct. This way, it can be used to easily make a decision based on the contents of the encapsulation header, "summarized" in this struct. In particular, it holds the IP address of the remote end (IPv4 or IPv6, depending on the case) in _key_**->remote_ipv4 **or _key_**->remote_ipv6**. Also, this struct exposes the _key_**->tunnel_id**, which is gener‐ ally mapped to a VNI (Virtual Network Identifier), making it programmable to‐ gether with the **bpf_skb_set_tunnel_key**() helper. Let's imagine that the following code is part of a program attached to the TC ingress interface, on one end of a GRE tunnel, and is supposed to filter out all messages coming from remote ends with IPv4 address other than 10.0.0.1: int ret; struct bpf_tunnel_key key = {}; ret = bpf_skb_get_tunnel_key(skb, &key, sizeof(key), 0); if (ret < 0) return TC_ACT_SHOT; // drop packet if (key.remote_ipv4 != 0x0a000001) return TC_ACT_SHOT; // drop packet return TC_ACT_OK; // accept packet This interface can also be used with all encapsulation devices that can operate in "collect metadata" mode: instead of having one network device per specific configuration, the "collect metadata" mode only requires a single device where the configuration can be extracted from this helper. This can be used together with various tunnels such as VXLan, Geneve, GRE or IP in IP (IPIP). **Return **0 on success, or a negative error in case of failure. **long bpf_skb_set_tunnel_key(struct sk_buff *_**skb_**, struct bpf_tunnel_key *_**key_**, u32 _**size_**, u64** _flags_**)** **Description** Populate tunnel metadata for packet associated to _skb._ The tunnel metadata is set to the contents of _key_, of _size_. The _flags_ can be set to a combination of the following values: **BPF_F_TUNINFO_IPV6** Indicate that the tunnel is based on IPv6 protocol instead of IPv4. **BPF_F_ZERO_CSUM_TX** For IPv4 packets, add a flag to tunnel metadata indicating that checksum computation should be skipped and checksum set to zeroes. **BPF_F_DONT_FRAGMENT** Add a flag to tunnel metadata indicating that the packet should not be fragmented. **BPF_F_SEQ_NUMBER** Add a flag to tunnel metadata indicating that a sequence number should be added to tunnel header before sending the packet. This flag was added for GRE encapsulation, but might be used with other protocols as well in the future. **BPF_F_NO_TUNNEL_KEY** Add a flag to tunnel metadata indicating that no tunnel key should be set in the resulting tunnel header. Here is a typical usage on the transmit path: struct bpf_tunnel_key key; populate key ... bpf_skb_set_tunnel_key(skb, &key, sizeof(key), 0); bpf_clone_redirect(skb, vxlan_dev_ifindex, 0); See also the description of the **bpf_skb_get_tunnel_key**() helper for additional information. **Return **0 on success, or a negative error in case of failure. **u64 bpf_perf_event_read(struct bpf_map *_**map_**, u64 _**flags_**)** **Description** Read the value of a perf event counter. This helper relies on a _map_ of type **BPF_MAP_TYPE_PERF_EVENT_ARRAY**. The nature of the perf event counter is selected when _map_ is updated with perf event file descriptors. The _map_ is an array whose size is the number of available CPUs, and each cell contains a value relative to one CPU. The value to retrieve is indicated by _flags_, that contains the in‐ dex of the CPU to look up, masked with **BPF_F_INDEX_MASK**. Alternatively, _flags_ can be set to **BPF_F_CURRENT_CPU **to indicate that the value for the current CPU should be retrieved. Note that before Linux 4.13, only hardware perf event can be retrieved. Also, be aware that the newer helper **bpf_perf_event_read_value**() is recommended over **bpf_perf_event_read**() in general. The latter has some ABI quirks where er‐ ror and counter value are used as a return code (which is wrong to do since ranges may overlap). This issue is fixed with **bpf_perf_event_read_value**(), which at the same time provides more features over the **bpf_perf_event_read**() interface. Please refer to the description of **bpf_perf_event_read_value**() for details. **Return **The value of the perf event counter read from the map, or a negative error code in case of failure. **long bpf_redirect(u32 _**ifindex_**, u64 _**flags_**)** **Description** Redirect the packet to another net device of index _ifindex_. This helper is somewhat similar to **bpf_clone_redirect**(), except that the packet is not cloned, which provides increased performance. Except for XDP, both ingress and egress interfaces can be used for redirection. The **BPF_F_INGRESS **value in _flags_ is used to make the distinction (ingress path is selected if the flag is present, egress path otherwise). Currently, XDP only supports redirection to the egress interface, and accepts no flag at all. The same effect can also be attained with the more generic **bpf_redirect_map**(), which uses a BPF map to store the redirect target instead of providing it di‐ rectly to the helper. **Return **For XDP, the helper returns **XDP_REDIRECT **on success or **XDP_ABORTED **on error. For other program types, the values are **TC_ACT_REDIRECT **on success or **TC_ACT_SHOT **on error. **u32 bpf_get_route_realm(struct sk_buff *_**skb_**)** **Description** Retrieve the realm or the route, that is to say the **tclassid **field of the des‐ tination for the _skb_. The identifier retrieved is a user-provided tag, similar to the one used with the net_cls cgroup (see description for **bpf_get_cgroup_classid**() helper), but here this tag is held by a route (a des‐ tination entry), not by a task. Retrieving this identifier works with the clsact TC egress hook (see also [**tc-bpf(8)](https://www.chedong.com/phpMan.php/man/tc-bpf/8/markdown)**), or alternatively on conventional classful egress qdiscs, but not on TC ingress path. In case of clsact TC egress hook, this has the advantage that, internally, the destination entry has not been dropped yet in the transmit path. Therefore, the destination entry does not need to be artificially held via **netif_keep_dst**() for a classful qdisc until the _skb_ is freed. This helper is available only if the kernel was compiled with **CON‐** **FIG_IP_ROUTE_CLASSID **configuration option. **Return **The realm of the route for the packet associated to _skb_, or 0 if none was found. **long bpf_perf_event_output(void *_**ctx_**, struct bpf_map *_**map_**, u64 _**flags_**, void *_**data_**, u64 _**size_**)** **Description** Write raw _data_ blob into a special BPF perf event held by _map_ of type **BPF_MAP_TYPE_PERF_EVENT_ARRAY**. This perf event must have the following attrib‐ utes: **PERF_SAMPLE_RAW **as **sample_type**, **PERF_TYPE_SOFTWARE **as **type**, and **PERF_COUNT_SW_BPF_OUTPUT **as **config**. The _flags_ are used to indicate the index in _map_ for which the value must be put, masked with **BPF_F_INDEX_MASK**. Alternatively, _flags_ can be set to **BPF_F_CURRENT_CPU **to indicate that the index of the current CPU core should be used. The value to write, of _size_, is passed through eBPF stack and pointed by _data_. The context of the program _ctx_ needs also be passed to the helper. On user space, a program willing to read the values needs to call **perf_event_open**() on the perf event (either for one or for all CPUs) and to store the file descriptor into the _map_. This must be done before the eBPF pro‐ gram can send data into it. An example is available in file _sam‐_ _ples/bpf/trace_output_user.c_ in the Linux kernel source tree (the eBPF program counterpart is in _samples/bpf/trace_output_kern.c_). **bpf_perf_event_output**() achieves better performance than **bpf_trace_printk**() for sharing data with user space, and is much better suitable for streaming data from eBPF programs. Note that this helper is not restricted to tracing use cases and can be used with programs attached to TC or XDP as well, where it allows for passing data to user space listeners. Data can be: • Only custom structs, • Only the packet payload, or • A combination of both. **Return **0 on success, or a negative error in case of failure. **long bpf_skb_load_bytes(const void *_**skb_**, u32 _**offset_**, void *_**to_**, u32 _**len_**)** **Description** This helper was provided as an easy way to load data from a packet. It can be used to load _len_ bytes from _offset_ from the packet associated to _skb_, into the buffer pointed by _to_. Since Linux 4.7, usage of this helper has mostly been replaced by "direct packet access", enabling packet data to be manipulated with _skb_**->data **and _skb_**->data_end **pointing respectively to the first byte of packet data and to the byte after the last byte of packet data. However, it remains useful if one wishes to read large quantities of data at once from a packet into the eBPF stack. **Return **0 on success, or a negative error in case of failure. **long bpf_get_stackid(void *_**ctx_**, struct bpf_map *_**map_**, u64 _**flags_**)** **Description** Walk a user or a kernel stack and return its id. To achieve this, the helper needs _ctx_, which is a pointer to the context on which the tracing program is executed, and a pointer to a _map_ of type **BPF_MAP_TYPE_STACK_TRACE**. The last argument, _flags_, holds the number of stack frames to skip (from 0 to 255), masked with **BPF_F_SKIP_FIELD_MASK**. The next bits can be used to set a combination of the following flags: **BPF_F_USER_STACK** Collect a user space stack instead of a kernel stack. **BPF_F_FAST_STACK_CMP** Compare stacks by hash only. **BPF_F_REUSE_STACKID** If two different stacks hash into the same _stackid_, discard the old one. The stack id retrieved is a 32 bit long integer handle which can be further combined with other data (including other stack ids) and used as a key into maps. This can be useful for generating a variety of graphs (such as flame graphs or off-cpu graphs). For walking a stack, this helper is an improvement over **bpf_probe_read**(), which can be used with unrolled loops but is not efficient and consumes a lot of eBPF instructions. Instead, **bpf_get_stackid**() can collect up to **PERF_MAX_STACK_DEPTH **both kernel and user frames. Note that this limit can be controlled with the **sysctl **program, and that it should be manually increased in order to profile long user stacks (such as stacks for Java programs). To do so, use: # sysctl kernel.perf_event_max_stack= **Return **The positive or null stack id on success, or a negative error in case of fail‐ ure. **s64 bpf_csum_diff(__be32 *_**from_**, u32 _**from_size_**, __be32 *_**to_**, u32 _**to_size_**, __wsum _**seed_**)** **Description** Compute a checksum difference, from the raw buffer pointed by _from_, of length _from_size_ (that must be a multiple of 4), towards the raw buffer pointed by _to_, of size _to_size_ (same remark). An optional _seed_ can be added to the value (this can be cascaded, the seed may come from a previous call to the helper). This is flexible enough to be used in several ways: • With _from_size_ == 0, _to_size_ > 0 and _seed_ set to checksum, it can be used when pushing new data. • With _from_size_ > 0, _to_size_ == 0 and _seed_ set to checksum, it can be used when removing data from a packet. • With _from_size_ > 0, _to_size_ > 0 and _seed_ set to 0, it can be used to compute a diff. Note that _from_size_ and _to_size_ do not need to be equal. This helper can be used in combination with **bpf_l3_csum_replace**() and **bpf_l4_csum_replace**(), to which one can feed in the difference computed with **bpf_csum_diff**(). **Return **The checksum result, or a negative error code in case of failure. **long bpf_skb_get_tunnel_opt(struct sk_buff *_**skb_**, void *_**opt_**, u32 _**size_**)** **Description** Retrieve tunnel options metadata for the packet associated to _skb_, and store the raw tunnel option data to the buffer _opt_ of _size_. This helper can be used with encapsulation devices that can operate in "collect metadata" mode (please refer to the related note in the description of **bpf_skb_get_tunnel_key**() for more details). A particular example where this can be used is in combination with the Geneve encapsulation protocol, where it al‐ lows for pushing (with **bpf_skb_get_tunnel_opt**() helper) and retrieving arbi‐ trary TLVs (Type-Length-Value headers) from the eBPF program. This allows for full customization of these headers. **Return **The size of the option data retrieved. **long bpf_skb_set_tunnel_opt(struct sk_buff *_**skb_**, void *_**opt_**, u32 _**size_**)** **Description** Set tunnel options metadata for the packet associated to _skb_ to the option data contained in the raw buffer _opt_ of _size_. See also the description of the **bpf_skb_get_tunnel_opt**() helper for additional information. **Return **0 on success, or a negative error in case of failure. **long bpf_skb_change_proto(struct sk_buff *_**skb_**, __be16 _**proto_**, u64 _**flags_**)** **Description** Change the protocol of the _skb_ to _proto_. Currently supported are transition from IPv4 to IPv6, and from IPv6 to IPv4. The helper takes care of the ground‐ work for the transition, including resizing the socket buffer. The eBPF program is expected to fill the new headers, if any, via **skb_store_bytes**() and to re‐ compute the checksums with **bpf_l3_csum_replace**() and **bpf_l4_csum_replace**(). The main case for this helper is to perform NAT64 operations out of an eBPF pro‐ gram. Internally, the GSO type is marked as dodgy so that headers are checked and segments are recalculated by the GSO/GRO engine. The size for GSO target is adapted as well. All values for _flags_ are reserved for future usage, and must be left at zero. A call to this helper is susceptible to change the underlying packet buffer. Therefore, at load time, all checks on pointers previously done by the verifier are invalidated and must be performed again, if the helper is used in combina‐ tion with direct packet access. **Return **0 on success, or a negative error in case of failure. **long bpf_skb_change_type(struct sk_buff *_**skb_**, u32 _**type_**)** **Description** Change the packet type for the packet associated to _skb_. This comes down to setting _skb_**->pkt_type **to _type_, except the eBPF program does not have a write access to _skb_**->pkt_type **beside this helper. Using a helper here allows for graceful handling of errors. The major use case is to change incoming _skb*s_ _to_ _**PACKET_HOST*_ in a program‐ matic way instead of having to recirculate via **redirect**(..., **BPF_F_INGRESS**), for example. Note that _type_ only allows certain values. At this time, they are: **PACKET_HOST** Packet is for us. **PACKET_BROADCAST** Send packet to all. **PACKET_MULTICAST** Send packet to group. **PACKET_OTHERHOST** Send packet to someone else. **Return **0 on success, or a negative error in case of failure. **long bpf_skb_under_cgroup(struct sk_buff *_**skb_**, struct bpf_map *_**map_**, u32 _**index_**)** **Description** Check whether _skb_ is a descendant of the cgroup2 held by _map_ of type **BPF_MAP_TYPE_CGROUP_ARRAY**, at _index_. **Return **The return value depends on the result of the test, and can be: • 0, if the _skb_ failed the cgroup2 descendant test. • 1, if the _skb_ succeeded the cgroup2 descendant test. • A negative error code, if an error occurred. **u32 bpf_get_hash_recalc(struct sk_buff *_**skb_**)** **Description** Retrieve the hash of the packet, _skb_**->hash**. If it is not set, in particular if the hash was cleared due to mangling, recompute this hash. Later accesses to the hash can be done directly with _skb_**->hash**. Calling **bpf_set_hash_invalid**(), changing a packet prototype with **bpf_skb_change_proto**(), or calling **bpf_skb_store_bytes**() with the **BPF_F_INVALI‐** **DATE_HASH **are actions susceptible to clear the hash and to trigger a new compu‐ tation for the next call to **bpf_get_hash_recalc**(). **Return **The 32-bit hash. ### u64 bpf_get_current_task(void) **Description** Get the current task. **Return **A pointer to the current task struct. **long bpf_probe_write_user(void *_**dst_**, const void *_**src_**, u32 _**len_**)** **Description** Attempt in a safe way to write _len_ bytes from the buffer _src_ to _dst_ in memory. It only works for threads that are in user context, and _dst_ must be a valid user space address. This helper should not be used to implement any kind of security mechanism be‐ cause of TOC-TOU attacks, but rather to debug, divert, and manipulate execution of semi-cooperative processes. Keep in mind that this feature is meant for experiments, and it has a risk of crashing the system and running programs. Therefore, when an eBPF program us‐ ing this helper is attached, a warning including PID and process name is printed to kernel logs. **Return **0 on success, or a negative error in case of failure. **long bpf_current_task_under_cgroup(struct bpf_map *_**map_**, u32 _**index_**)** **Description** Check whether the probe is being run is the context of a given subset of the cgroup2 hierarchy. The cgroup2 to test is held by _map_ of type **BPF_MAP_TYPE_CGROUP_ARRAY**, at _index_. **Return **The return value depends on the result of the test, and can be: • 1, if current task belongs to the cgroup2. • 0, if current task does not belong to the cgroup2. • A negative error code, if an error occurred. **long bpf_skb_change_tail(struct sk_buff *_**skb_**, u32 _**len_**, u64 _**flags_**)** **Description** Resize (trim or grow) the packet associated to _skb_ to the new _len_. The _flags_ are reserved for future usage, and must be left at zero. The basic idea is that the helper performs the needed work to change the size of the packet, then the eBPF program rewrites the rest via helpers like **bpf_skb_store_bytes**(), **bpf_l3_csum_replace**(), **bpf_l3_csum_replace**() and others. This helper is a slow path utility intended for replies with control messages. And because it is targeted for slow path, the helper itself can afford to be slow: it implicitly linearizes, unclones and drops offloads from the _skb_. A call to this helper is susceptible to change the underlying packet buffer. Therefore, at load time, all checks on pointers previously done by the verifier are invalidated and must be performed again, if the helper is used in combina‐ tion with direct packet access. **Return **0 on success, or a negative error in case of failure. **long bpf_skb_pull_data(struct sk_buff *_**skb_**, u32 _**len_**)** **Description** Pull in non-linear data in case the _skb_ is non-linear and not all of _len_ are part of the linear section. Make _len_ bytes from _skb_ readable and writable. If a zero value is passed for _len_, then all bytes in the linear part of _skb_ will be made readable and writable. This helper is only needed for reading and writing with direct packet access. For direct packet access, testing that offsets to access are within packet boundaries (test on _skb_**->data_end**) is susceptible to fail if offsets are in‐ valid, or if the requested data is in non-linear parts of the _skb_. On failure the program can just bail out, or in the case of a non-linear buffer, use a helper to make the data available. The **bpf_skb_load_bytes**() helper is a first solution to access the data. Another one consists in using **bpf_skb_pull_data **to pull in once the non-linear parts, then retesting and eventually access the data. At the same time, this also makes sure the _skb_ is uncloned, which is a neces‐ sary condition for direct write. As this needs to be an invariant for the write part only, the verifier detects writes and adds a prologue that is calling **bpf_skb_pull_data() **to effectively unclone the _skb_ from the very beginning in case it is indeed cloned. A call to this helper is susceptible to change the underlying packet buffer. Therefore, at load time, all checks on pointers previously done by the verifier are invalidated and must be performed again, if the helper is used in combina‐ tion with direct packet access. **Return **0 on success, or a negative error in case of failure. **s64 bpf_csum_update(struct sk_buff *_**skb_**, __wsum _**csum_**)** **Description** Add the checksum _csum_ into _skb_**->csum **in case the driver has supplied a checksum for the entire packet into that field. Return an error otherwise. This helper is intended to be used in combination with **bpf_csum_diff**(), in particular when the checksum needs to be updated after data has been written into the packet through direct packet access. **Return **The checksum on success, or a negative error code in case of failure. **void bpf_set_hash_invalid(struct sk_buff *_**skb_**)** **Description** Invalidate the current _skb_**->hash**. It can be used after mangling on headers through direct packet access, in order to indicate that the hash is outdated and to trigger a recalculation the next time the kernel tries to access this hash or when the **bpf_get_hash_recalc**() helper is called. **Return **void. ### long bpf_get_numa_node_id(void) **Description** Return the id of the current NUMA node. The primary use case for this helper is the selection of sockets for the local NUMA node, when the program is attached to sockets using the **SO_ATTACH_REUSEPORT_EBPF **option (see also [**socket(7)](https://www.chedong.com/phpMan.php/man/socket/7/markdown)**), but the helper is also available to other eBPF program types, similarly to **bpf_get_smp_processor_id**(). **Return **The id of current NUMA node. **long bpf_skb_change_head(struct sk_buff *_**skb_**, u32 _**len_**, u64 _**flags_**)** **Description** Grows headroom of packet associated to _skb_ and adjusts the offset of the MAC header accordingly, adding _len_ bytes of space. It automatically extends and re‐ allocates memory as required. This helper can be used on a layer 3 _skb_ to push a MAC header for redirection into a layer 2 device. All values for _flags_ are reserved for future usage, and must be left at zero. A call to this helper is susceptible to change the underlying packet buffer. Therefore, at load time, all checks on pointers previously done by the verifier are invalidated and must be performed again, if the helper is used in combina‐ tion with direct packet access. **Return **0 on success, or a negative error in case of failure. **long bpf_xdp_adjust_head(struct xdp_buff *_**xdp_md_**, int _**delta_**)** **Description** Adjust (move) _xdp_md_**->data **by _delta_ bytes. Note that it is possible to use a negative value for _delta_. This helper can be used to prepare the packet for pushing or popping headers. A call to this helper is susceptible to change the underlying packet buffer. Therefore, at load time, all checks on pointers previously done by the verifier are invalidated and must be performed again, if the helper is used in combina‐ tion with direct packet access. **Return **0 on success, or a negative error in case of failure. **long bpf_probe_read_str(void *_**dst_**, u32 _**size_**, const void *_**unsafe_ptr_**)** **Description** Copy a NUL terminated string from an unsafe kernel address _unsafe_ptr_ to _dst_. See **bpf_probe_read_kernel_str**() for more details. Generally, use **bpf_probe_read_user_str**() or **bpf_probe_read_kernel_str**() in‐ stead. **Return **On success, the strictly positive length of the string, including the trailing NUL character. On error, a negative value. **u64 bpf_get_socket_cookie(struct sk_buff *_**skb_**)** **Description** If the **struct sk_buff **pointed by _skb_ has a known socket, retrieve the cookie (generated by the kernel) of this socket. If no cookie has been set yet, gen‐ erate a new cookie. Once generated, the socket cookie remains stable for the life of the socket. This helper can be useful for monitoring per socket net‐ working traffic statistics as it provides a global socket identifier that can be assumed unique. **Return **A 8-byte long unique number on success, or 0 if the socket field is missing in‐ side _skb_. **u64 bpf_get_socket_cookie(struct bpf_sock_addr *_**ctx_**)** **Description** Equivalent to bpf_get_socket_cookie() helper that accepts _skb_, but gets socket from **struct bpf_sock_addr **context. **Return **A 8-byte long unique number. **u64 bpf_get_socket_cookie(struct bpf_sock_ops *_**ctx_**)** **Description** Equivalent to **bpf_get_socket_cookie**() helper that accepts _skb_, but gets socket from **struct bpf_sock_ops **context. **Return **A 8-byte long unique number. **u64 bpf_get_socket_cookie(struct sock *_**sk_**)** **Description** Equivalent to **bpf_get_socket_cookie**() helper that accepts _sk_, but gets socket from a BTF **struct sock**. This helper also works for sleepable programs. **Return **A 8-byte long unique number or 0 if _sk_ is NULL. **u32 bpf_get_socket_uid(struct sk_buff *_**skb_**)** **Description** Get the owner UID of the socked associated to _skb_. **Return **The owner UID of the socket associated to _skb_. If the socket is **NULL**, or if it is not a full socket (i.e. if it is a time-wait or a request socket instead), **overflowuid **value is returned (note that **overflowuid **might also be the actual UID value for the socket). **long bpf_set_hash(struct sk_buff *_**skb_**, u32 _**hash_**)** **Description** Set the full hash for _skb_ (set the field _skb_**->hash**) to value _hash_. **Return **0 **long bpf_setsockopt(void *_**bpf_socket_**, int _**level_**, int _**optname_**, void *_**optval_**, int _**optlen_**)** **Description** Emulate a call to **setsockopt() **on the socket associated to _bpf_socket_, which must be a full socket. The _level_ at which the option resides and the name _opt‐_ _name_ of the option must be specified, see [**setsockopt(2)](https://www.chedong.com/phpMan.php/man/setsockopt/2/markdown) **for more information. The option value of length _optlen_ is pointed by _optval_. _bpf_socket_ should be one of the following: • **struct bpf_sock_ops **for **BPF_PROG_TYPE_SOCK_OPS**. • **struct bpf_sock_addr **for **BPF_CGROUP_INET4_CONNECT**, **BPF_CGROUP_INET6_CONNECT** and **BPF_CGROUP_UNIX_CONNECT**. This helper actually implements a subset of **setsockopt()**. It supports the fol‐ lowing _level_s: • **SOL_SOCKET**, which supports the following _optname_s: **SO_RCVBUF**, **SO_SNDBUF**, **SO_MAX_PACING_RATE**, **SO_PRIORITY**, **SO_RCVLOWAT**, **SO_MARK**, **SO_BINDTODEVICE**, **SO_KEEPALIVE**, **SO_REUSEADDR**, **SO_REUSEPORT**, **SO_BINDTOIFINDEX**, **SO_TXREHASH**. • **IPPROTO_TCP**, which supports the following _optname_s: **TCP_CONGESTION**, **TCP_BPF_IW**, **TCP_BPF_SNDCWND_CLAMP**, **TCP_SAVE_SYN**, **TCP_KEEPIDLE**, **TCP_KEEPINTVL**, **TCP_KEEPCNT**, **TCP_SYNCNT**, **TCP_USER_TIMEOUT**, **TCP_NOTSENT_LOWAT**, **TCP_NODELAY**, **TCP_MAXSEG**, **TCP_WINDOW_CLAMP**, **TCP_THIN_LINEAR_TIMEOUTS**, **TCP_BPF_DELACK_MAX**, **TCP_BPF_RTO_MIN**. • **IPPROTO_IP**, which supports _optname_ **IP_TOS**. • **IPPROTO_IPV6**, which supports the following _optname_s: **IPV6_TCLASS**, **IPV6_AUT‐** **OFLOWLABEL**. **Return **0 on success, or a negative error in case of failure. **long bpf_skb_adjust_room(struct sk_buff *_**skb_**, s32 _**len_diff_**, u32 _**mode_**, u64 _**flags_**)** **Description** Grow or shrink the room for data in the packet associated to _skb_ by _len_diff_, and according to the selected _mode_. By default, the helper will reset any offloaded checksum indicator of the skb to CHECKSUM_NONE. This can be avoided by the following flag: • **BPF_F_ADJ_ROOM_NO_CSUM_RESET**: Do not reset offloaded checksum data of the skb to CHECKSUM_NONE. There are two supported modes at this time: • **BPF_ADJ_ROOM_MAC**: Adjust room at the mac layer (room space is added or re‐ moved between the layer 2 and layer 3 headers). • **BPF_ADJ_ROOM_NET**: Adjust room at the network layer (room space is added or removed between the layer 3 and layer 4 headers). The following flags are supported at this time: • **BPF_F_ADJ_ROOM_FIXED_GSO**: Do not adjust gso_size. Adjusting mss in this way is not allowed for datagrams. • **BPF_F_ADJ_ROOM_ENCAP_L3_IPV4**, **BPF_F_ADJ_ROOM_ENCAP_L3_IPV6**: Any new space is reserved to hold a tunnel header. Configure skb offsets and other fields ac‐ cordingly. • **BPF_F_ADJ_ROOM_ENCAP_L4_GRE**, **BPF_F_ADJ_ROOM_ENCAP_L4_UDP**: Use with ENCAP_L3 flags to further specify the tunnel type. • **BPF_F_ADJ_ROOM_ENCAP_L2**(_len_): Use with ENCAP_L3/L4 flags to further specify the tunnel type; _len_ is the length of the inner MAC header. • **BPF_F_ADJ_ROOM_ENCAP_L2_ETH**: Use with BPF_F_ADJ_ROOM_ENCAP_L2 flag to further specify the L2 type as Ethernet. • **BPF_F_ADJ_ROOM_DECAP_L3_IPV4**, **BPF_F_ADJ_ROOM_DECAP_L3_IPV6**: Indicate the new IP header version after decapsulating the outer IP header. Used when the in‐ ner and outer IP versions are different. A call to this helper is susceptible to change the underlying packet buffer. Therefore, at load time, all checks on pointers previously done by the verifier are invalidated and must be performed again, if the helper is used in combina‐ tion with direct packet access. **Return **0 on success, or a negative error in case of failure. **long bpf_redirect_map(struct bpf_map *_**map_**, u64 _**key_**, u64 _**flags_**)** **Description** Redirect the packet to the endpoint referenced by _map_ at index _key_. Depending on its type, this _map_ can contain references to net devices (for forwarding packets through other ports), or to CPUs (for redirecting XDP frames to another CPU; but this is only implemented for native XDP (with driver support) as of this writing). The lower two bits of _flags_ are used as the return code if the map lookup fails. This is so that the return value can be one of the XDP program return codes up to **XDP_TX**, as chosen by the caller. The higher bits of _flags_ can be set to BPF_F_BROADCAST or BPF_F_EXCLUDE_INGRESS as defined below. With BPF_F_BROADCAST the packet will be broadcasted to all the interfaces in the map, with BPF_F_EXCLUDE_INGRESS the ingress interface will be excluded when do broadcasting. See also **bpf_redirect**(), which only supports redirecting to an ifindex, but doesn't require a map to do so. **Return XDP_REDIRECT **on success, or the value of the two lower bits of the _flags_ argu‐ ment on error. **long bpf_sk_redirect_map(struct sk_buff *_**skb_**, struct bpf_map *_**map_**, u32 _**key_**, u64 _**flags_**)** **Description** Redirect the packet to the socket referenced by _map_ (of type **BPF_MAP_TYPE_SOCKMAP**) at index _key_. Both ingress and egress interfaces can be used for redirection. The **BPF_F_INGRESS **value in _flags_ is used to make the dis‐ tinction (ingress path is selected if the flag is present, egress path other‐ wise). This is the only flag supported for now. **Return SK_PASS **on success, or **SK_DROP **on error. **long bpf_sock_map_update(struct bpf_sock_ops *_**skops_**, struct bpf_map *_**map_**, void *_**key_**, u64** _flags_**)** **Description** Add an entry to, or update a _map_ referencing sockets. The _skops_ is used as a new value for the entry associated to _key_. _flags_ is one of: **BPF_NOEXIST** The entry for _key_ must not exist in the map. **BPF_EXIST** The entry for _key_ must already exist in the map. **BPF_ANY** No condition on the existence of the entry for _key_. If the _map_ has eBPF programs (parser and verdict), those will be inherited by the socket being added. If the socket is already attached to eBPF programs, this results in an error. **Return **0 on success, or a negative error in case of failure. **long bpf_xdp_adjust_meta(struct xdp_buff *_**xdp_md_**, int _**delta_**)** **Description** Adjust the address pointed by _xdp_md_**->data_meta **by _delta_ (which can be positive or negative). Note that this operation modifies the address stored in _xdp_md_**->data**, so the latter must be loaded only after the helper has been called. The use of _xdp_md_**->data_meta **is optional and programs are not required to use it. The rationale is that when the packet is processed with XDP (e.g. as DoS filter), it is possible to push further meta data along with it before passing to the stack, and to give the guarantee that an ingress eBPF program attached as a TC classifier on the same device can pick this up for further post-pro‐ cessing. Since TC works with socket buffers, it remains possible to set from XDP the **mark **or **priority **pointers, or other pointers for the socket buffer. Having this scratch space generic and programmable allows for more flexibility as the user is free to store whatever meta data they need. A call to this helper is susceptible to change the underlying packet buffer. Therefore, at load time, all checks on pointers previously done by the verifier are invalidated and must be performed again, if the helper is used in combina‐ tion with direct packet access. **Return **0 on success, or a negative error in case of failure. **long bpf_perf_event_read_value(struct bpf_map *_**map_**, u64 _**flags_**, struct bpf_perf_event_value** ***_**buf_**, u32 _**buf_size_**)** **Description** Read the value of a perf event counter, and store it into _buf_ of size _buf_size_. This helper relies on a _map_ of type **BPF_MAP_TYPE_PERF_EVENT_ARRAY**. The nature of the perf event counter is selected when _map_ is updated with perf event file descriptors. The _map_ is an array whose size is the number of available CPUs, and each cell contains a value relative to one CPU. The value to retrieve is indicated by _flags_, that contains the index of the CPU to look up, masked with **BPF_F_INDEX_MASK**. Alternatively, _flags_ can be set to **BPF_F_CURRENT_CPU **to indi‐ cate that the value for the current CPU should be retrieved. This helper behaves in a way close to **bpf_perf_event_read**() helper, save that instead of just returning the value observed, it fills the _buf_ structure. This allows for additional data to be retrieved: in particular, the enabled and run‐ ning times (in _buf_**->enabled **and _buf_**->running**, respectively) are copied. In gen‐ eral, **bpf_perf_event_read_value**() is recommended over **bpf_perf_event_read**(), which has some ABI issues and provides fewer functionalities. These values are interesting, because hardware PMU (Performance Monitoring Unit) counters are limited resources. When there are more PMU based perf events opened than available counters, kernel will multiplex these events so each event gets certain percentage (but not all) of the PMU time. In case that mul‐ tiplexing happens, the number of samples or counter value will not reflect the case compared to when no multiplexing occurs. This makes comparison between different runs difficult. Typically, the counter value should be normalized before comparing to other experiments. The usual normalization is done as fol‐ lows. normalized_counter = counter * t_enabled / t_running Where t_enabled is the time enabled for event and t_running is the time running for event since last normalization. The enabled and running times are accumu‐ lated since the perf event open. To achieve scaling factor between two invoca‐ tions of an eBPF program, users can use CPU id as the key (which is typical for perf array usage model) to remember the previous value and do the calculation inside the eBPF program. **Return **0 on success, or a negative error in case of failure. **long bpf_perf_prog_read_value(struct bpf_perf_event_data *_**ctx_**, struct bpf_perf_event_value** ***_**buf_**, u32 _**buf_size_**)** **Description** For an eBPF program attached to a perf event, retrieve the value of the event counter associated to _ctx_ and store it in the structure pointed by _buf_ and of size _buf_size_. Enabled and running times are also stored in the structure (see description of helper **bpf_perf_event_read_value**() for more details). **Return **0 on success, or a negative error in case of failure. **long bpf_getsockopt(void *_**bpf_socket_**, int _**level_**, int _**optname_**, void *_**optval_**, int _**optlen_**)** **Description** Emulate a call to **getsockopt() **on the socket associated to _bpf_socket_, which must be a full socket. The _level_ at which the option resides and the name _opt‐_ _name_ of the option must be specified, see [**getsockopt(2)](https://www.chedong.com/phpMan.php/man/getsockopt/2/markdown) **for more information. The retrieved value is stored in the structure pointed by _opval_ and of length _optlen_. _bpf_socket_ should be one of the following: • **struct bpf_sock_ops **for **BPF_PROG_TYPE_SOCK_OPS**. • **struct bpf_sock_addr **for **BPF_CGROUP_INET4_CONNECT**, **BPF_CGROUP_INET6_CONNECT** and **BPF_CGROUP_UNIX_CONNECT**. This helper actually implements a subset of **getsockopt()**. It supports the same set of _optname_s that is supported by the **bpf_setsockopt**() helper. The excep‐ tions are **TCP_BPF_* **is **bpf_setsockopt**() only and **TCP_SAVED_SYN **is **bpf_getsock‐** **opt**() only. **Return **0 on success, or a negative error in case of failure. **long bpf_override_return(struct pt_regs *_**regs_**, u64 _**rc_**)** **Description** Used for error injection, this helper uses kprobes to override the return value of the probed function, and to set it to _rc_. The first argument is the context _regs_ on which the kprobe works. This helper works by setting the PC (program counter) to an override function which is run in place of the original probed function. This means the probed function is not run at all. The replacement function just returns with the re‐ quired value. This helper has security implications, and thus is subject to restrictions. It is only available if the kernel was compiled with the **CONFIG_BPF_KPROBE_OVER‐** **RIDE **configuration option, and in this case it only works on functions tagged with **ALLOW_ERROR_INJECTION **in the kernel code. Also, the helper is only available for the architectures having the CON‐ FIG_FUNCTION_ERROR_INJECTION option. As of this writing, x86 architecture is the only one to support this feature. **Return **0 **long bpf_sock_ops_cb_flags_set(struct bpf_sock_ops *_**bpf_sock_**, int _**argval_**)** **Description** Attempt to set the value of the **bpf_sock_ops_cb_flags **field for the full TCP socket associated to _bpf_sock_ops_ to _argval_. The primary use of this field is to determine if there should be calls to eBPF programs of type **BPF_PROG_TYPE_SOCK_OPS **at various points in the TCP code. A program of the same type can change its value, per connection and as necessary, when the connection is established. This field is directly accessible for read‐ ing, but this helper must be used for updates in order to return an error if an eBPF program tries to set a callback that is not supported in the current ker‐ nel. _argval_ is a flag array which can combine these flags: • **BPF_SOCK_OPS_RTO_CB_FLAG **(retransmission time out) • **BPF_SOCK_OPS_RETRANS_CB_FLAG **(retransmission) • **BPF_SOCK_OPS_STATE_CB_FLAG **(TCP state change) • **BPF_SOCK_OPS_RTT_CB_FLAG **(every RTT) Therefore, this function can be used to clear a callback flag by setting the appropriate bit to zero. e.g. to disable the RTO callback: **bpf_sock_ops_cb_flags_set(bpf_sock,** **bpf_sock->bpf_sock_ops_cb_flags & ~BPF_SOCK_OPS_RTO_CB_FLAG)** Here are some examples of where one could call such eBPF program: • When RTO fires. • When a packet is retransmitted. • When the connection terminates. • When a packet is sent. • When a packet is received. **Return **Code **-EINVAL **if the socket is not a full TCP socket; otherwise, a positive num‐ ber containing the bits that could not be set is returned (which comes down to 0 if all bits were set as required). **long bpf_msg_redirect_map(struct sk_msg_buff *_**msg_**, struct bpf_map *_**map_**, u32 _**key_**, u64 _**flags_**)** **Description** This helper is used in programs implementing policies at the socket level. If the message _msg_ is allowed to pass (i.e. if the verdict eBPF program returns **SK_PASS**), redirect it to the socket referenced by _map_ (of type **BPF_MAP_TYPE_SOCKMAP**) at index _key_. Both ingress and egress interfaces can be used for redirection. The **BPF_F_INGRESS **value in _flags_ is used to make the dis‐ tinction (ingress path is selected if the flag is present, egress path other‐ wise). This is the only flag supported for now. **Return SK_PASS **on success, or **SK_DROP **on error. **long bpf_msg_apply_bytes(struct sk_msg_buff *_**msg_**, u32 _**bytes_**)** **Description** For socket policies, apply the verdict of the eBPF program to the next _bytes_ (number of bytes) of message _msg_. For example, this helper can be used in the following cases: • A single **sendmsg**() or **sendfile**() system call contains multiple logical mes‐ sages that the eBPF program is supposed to read and for which it should apply a verdict. • An eBPF program only cares to read the first _bytes_ of a _msg_. If the message has a large payload, then setting up and calling the eBPF program repeatedly for all bytes, even though the verdict is already known, would create unnec‐ essary overhead. When called from within an eBPF program, the helper sets a counter internal to the BPF infrastructure, that is used to apply the last verdict to the next _bytes_. If _bytes_ is smaller than the current data being processed from a **sendmsg**() or **sendfile**() system call, the first _bytes_ will be sent and the eBPF program will be re-run with the pointer for start of data pointing to byte num‐ ber _bytes_ **+ 1**. If _bytes_ is larger than the current data being processed, then the eBPF verdict will be applied to multiple **sendmsg**() or **sendfile**() calls un‐ til _bytes_ are consumed. Note that if a socket closes with the internal counter holding a non-zero value, this is not a problem because data is not being buffered for _bytes_ and is sent as it is received. **Return **0 **long bpf_msg_cork_bytes(struct sk_msg_buff *_**msg_**, u32 _**bytes_**)** **Description** For socket policies, prevent the execution of the verdict eBPF program for mes‐ sage _msg_ until _bytes_ (byte number) have been accumulated. This can be used when one needs a specific number of bytes before a verdict can be assigned, even if the data spans multiple **sendmsg**() or **sendfile**() calls. The extreme case would be a user calling **sendmsg**() repeatedly with 1-byte long mes‐ sage segments. Obviously, this is bad for performance, but it is still valid. If the eBPF program needs _bytes_ bytes to validate a header, this helper can be used to prevent the eBPF program to be called again until _bytes_ have been accu‐ mulated. **Return **0 **long bpf_msg_pull_data(struct sk_msg_buff *_**msg_**, u32 _**start_**, u32 _**end_**, u64 _**flags_**)** **Description** For socket policies, pull in non-linear data from user space for _msg_ and set pointers _msg_**->data **and _msg_**->data_end **to _start_ and _end_ bytes offsets into _msg_, respectively. If a program of type **BPF_PROG_TYPE_SK_MSG **is run on a _msg_ it can only parse data that the (**data**, **data_end**) pointers have already consumed. For **sendmsg**() hooks this is likely the first scatterlist element. But for calls relying on the **sendpage **handler (e.g. **sendfile**()) this will be the range (**0**, **0**) because the data is shared with user space and by default the objective is to avoid al‐ lowing user space to modify data while (or after) eBPF verdict is being de‐ cided. This helper can be used to pull in data and to set the start and end pointer to given values. Data will be copied if necessary (i.e. if data was not linear and if start and end pointers do not point to the same chunk). A call to this helper is susceptible to change the underlying packet buffer. Therefore, at load time, all checks on pointers previously done by the verifier are invalidated and must be performed again, if the helper is used in combina‐ tion with direct packet access. All values for _flags_ are reserved for future usage, and must be left at zero. **Return **0 on success, or a negative error in case of failure. **long bpf_bind(struct bpf_sock_addr *_**ctx_**, struct sockaddr *_**addr_**, int _**addr_len_**)** **Description** Bind the socket associated to _ctx_ to the address pointed by _addr_, of length _addr_len_. This allows for making outgoing connection from the desired IP ad‐ dress, which can be useful for example when all processes inside a cgroup should use one single IP address on a host that has multiple IP configured. This helper works for IPv4 and IPv6, TCP and UDP sockets. The domain (_addr_**->sa_family**) must be **AF_INET **(or **AF_INET6**). It's advised to pass zero port (**sin_port **or **sin6_port**) which triggers IP_BIND_ADDRESS_NO_PORT-like behavior and lets the kernel efficiently pick up an unused port as long as 4-tuple is unique. Passing non-zero port might lead to degraded performance. **Return **0 on success, or a negative error in case of failure. **long bpf_xdp_adjust_tail(struct xdp_buff *_**xdp_md_**, int _**delta_**)** **Description** Adjust (move) _xdp_md_**->data_end **by _delta_ bytes. It is possible to both shrink and grow the packet tail. Shrink done via _delta_ being a negative integer. A call to this helper is susceptible to change the underlying packet buffer. Therefore, at load time, all checks on pointers previously done by the verifier are invalidated and must be performed again, if the helper is used in combina‐ tion with direct packet access. **Return **0 on success, or a negative error in case of failure. **long bpf_skb_get_xfrm_state(struct sk_buff *_**skb_**, u32 _**index_**, struct bpf_xfrm_state** ***_**xfrm_state_**, u32 _**size_**, u64 _**flags_**)** **Description** Retrieve the XFRM state (IP transform framework, see also [**ip-xfrm(8)](https://www.chedong.com/phpMan.php/man/ip-xfrm/8/markdown)**) at _index_ in XFRM "security path" for _skb_. The retrieved value is stored in the **struct bpf_xfrm_state **pointed by _xfrm_state_ and of length _size_. All values for _flags_ are reserved for future usage, and must be left at zero. This helper is available only if the kernel was compiled with **CONFIG_XFRM **con‐ figuration option. **Return **0 on success, or a negative error in case of failure. **long bpf_get_stack(void *_**ctx_**, void *_**buf_**, u32 _**size_**, u64 _**flags_**)** **Description** Return a user or a kernel stack in bpf program provided buffer. To achieve this, the helper needs _ctx_, which is a pointer to the context on which the tracing program is executed. To store the stacktrace, the bpf program provides _buf_ with a nonnegative _size_. The last argument, _flags_, holds the number of stack frames to skip (from 0 to 255), masked with **BPF_F_SKIP_FIELD_MASK**. The next bits can be used to set the following flags: **BPF_F_USER_STACK** Collect a user space stack instead of a kernel stack. **BPF_F_USER_BUILD_ID** Collect (build_id, file_offset) instead of ips for user stack, only valid if **BPF_F_USER_STACK **is also specified. _file_offset_ is an offset relative to the beginning of the executable or shared object file backing the vma which the _ip_ falls in. It is _not_ an offset relative to that object's base address. Accordingly, it must be adjusted by adding (sh_addr - sh_offset), where sh_{addr,offset} corre‐ spond to the executable section containing _file_offset_ in the object, for comparisons to symbols' st_value to be valid. **bpf_get_stack**() can collect up to **PERF_MAX_STACK_DEPTH **both kernel and user frames, subject to sufficient large buffer size. Note that this limit can be controlled with the **sysctl **program, and that it should be manually increased in order to profile long user stacks (such as stacks for Java programs). To do so, use: # sysctl kernel.perf_event_max_stack= **Return **The non-negative copied _buf_ length equal to or less than _size_ on success, or a negative error in case of failure. **long bpf_skb_load_bytes_relative(const void *_**skb_**, u32 _**offset_**, void *_**to_**, u32 _**len_**, u32** _start_header_**)** **Description** This helper is similar to **bpf_skb_load_bytes**() in that it provides an easy way to load _len_ bytes from _offset_ from the packet associated to _skb_, into the buffer pointed by _to_. The difference to **bpf_skb_load_bytes**() is that a fifth argument _start_header_ exists in order to select a base offset to start from. _start_header_ can be one of: **BPF_HDR_START_MAC** Base offset to load data from is _skb_'s mac header. **BPF_HDR_START_NET** Base offset to load data from is _skb_'s network header. In general, "direct packet access" is the preferred method to access packet data, however, this helper is in particular useful in socket filters where _skb_**->data **does not always point to the start of the mac header and where "di‐ rect packet access" is not available. **Return **0 on success, or a negative error in case of failure. **long bpf_fib_lookup(void *_**ctx_**, struct bpf_fib_lookup *_**params_**, int _**plen_**, u32 _**flags_**)** **Description** Do FIB lookup in kernel tables using parameters in _params_. If lookup is suc‐ cessful and result shows packet is to be forwarded, the neighbor tables are searched for the nexthop. If successful (ie., FIB lookup shows forwarding and nexthop is resolved), the nexthop address is returned in ipv4_dst or ipv6_dst based on family, smac is set to mac address of egress device, dmac is set to nexthop mac address, rt_metric is set to metric from route (IPv4/IPv6 only), and ifindex is set to the device index of the nexthop from the FIB lookup. _plen_ argument is the size of the passed in struct. _flags_ argument can be a combination of one or more of the following values: **BPF_FIB_LOOKUP_DIRECT** Do a direct table lookup vs full lookup using FIB rules. **BPF_FIB_LOOKUP_TBID** Used with BPF_FIB_LOOKUP_DIRECT. Use the routing table ID present in _params_->tbid for the fib lookup. **BPF_FIB_LOOKUP_OUTPUT** Perform lookup from an egress perspective (default is ingress). **BPF_FIB_LOOKUP_SKIP_NEIGH** Skip the neighbour table lookup. _params_->dmac and _params_->smac will not be set as output. A common use case is to call **bpf_redirect_neigh**() af‐ ter doing **bpf_fib_lookup**(). **BPF_FIB_LOOKUP_SRC** Derive and set source IP addr in _params_->ipv{4,6}_src for the nexthop. If the src addr cannot be derived, **BPF_FIB_LKUP_RET_NO_SRC_ADDR **is re‐ turned. In this case, _params_->dmac and _params_->smac are not set either. _ctx_ is either **struct xdp_md **for XDP programs or **struct sk_buff **tc cls_act pro‐ grams. **Return** • < 0 if any input argument is invalid • 0 on success (packet is forwarded, nexthop neighbor exists) • > 0 one of **BPF_FIB_LKUP_RET_ **codes explaining why the packet is not forwarded or needs assist from full stack If lookup fails with BPF_FIB_LKUP_RET_FRAG_NEEDED, then the MTU was exceeded and output params->mtu_result contains the MTU. **long bpf_sock_hash_update(struct bpf_sock_ops *_**skops_**, struct bpf_map *_**map_**, void *_**key_**, u64** _flags_**)** **Description** Add an entry to, or update a sockhash _map_ referencing sockets. The _skops_ is used as a new value for the entry associated to _key_. _flags_ is one of: **BPF_NOEXIST** The entry for _key_ must not exist in the map. **BPF_EXIST** The entry for _key_ must already exist in the map. **BPF_ANY** No condition on the existence of the entry for _key_. If the _map_ has eBPF programs (parser and verdict), those will be inherited by the socket being added. If the socket is already attached to eBPF programs, this results in an error. **Return **0 on success, or a negative error in case of failure. **long bpf_msg_redirect_hash(struct sk_msg_buff *_**msg_**, struct bpf_map *_**map_**, void *_**key_**, u64** _flags_**)** **Description** This helper is used in programs implementing policies at the socket level. If the message _msg_ is allowed to pass (i.e. if the verdict eBPF program returns **SK_PASS**), redirect it to the socket referenced by _map_ (of type **BPF_MAP_TYPE_SOCKHASH**) using hash _key_. Both ingress and egress interfaces can be used for redirection. The **BPF_F_INGRESS **value in _flags_ is used to make the distinction (ingress path is selected if the flag is present, egress path oth‐ erwise). This is the only flag supported for now. **Return SK_PASS **on success, or **SK_DROP **on error. **long bpf_sk_redirect_hash(struct sk_buff *_**skb_**, struct bpf_map *_**map_**, void *_**key_**, u64 _**flags_**)** **Description** This helper is used in programs implementing policies at the skb socket level. If the sk_buff _skb_ is allowed to pass (i.e. if the verdict eBPF program re‐ turns **SK_PASS**), redirect it to the socket referenced by _map_ (of type **BPF_MAP_TYPE_SOCKHASH**) using hash _key_. Both ingress and egress interfaces can be used for redirection. The **BPF_F_INGRESS **value in _flags_ is used to make the distinction (ingress path is selected if the flag is present, egress other‐ wise). This is the only flag supported for now. **Return SK_PASS **on success, or **SK_DROP **on error. **long bpf_lwt_push_encap(struct sk_buff *_**skb_**, u32 _**type_**, void *_**hdr_**, u32 _**len_**)** **Description** Encapsulate the packet associated to _skb_ within a Layer 3 protocol header. This header is provided in the buffer at address _hdr_, with _len_ its size in bytes. _type_ indicates the protocol of the header and can be one of: **BPF_LWT_ENCAP_SEG6** IPv6 encapsulation with Segment Routing Header (**struct ipv6_sr_hdr**). _hdr_ only contains the SRH, the IPv6 header is computed by the kernel. **BPF_LWT_ENCAP_SEG6_INLINE** Only works if _skb_ contains an IPv6 packet. Insert a Segment Routing Header (**struct ipv6_sr_hdr**) inside the IPv6 header. **BPF_LWT_ENCAP_IP** IP encapsulation (GRE/GUE/IPIP/etc). The outer header must be IPv4 or IPv6, followed by zero or more additional headers, up to **LWT_BPF_MAX_HEADROOM **total bytes in all prepended headers. Please note that if **skb_is_gso**(_skb_) is true, no more than two headers can be prepended, and the inner header, if present, should be either GRE or UDP/GUE. **BPF_LWT_ENCAP_SEG6*** types can be called by BPF programs of type **BPF_PROG_TYPE_LWT_IN**; **BPF_LWT_ENCAP_IP **type can be called by bpf programs of types **BPF_PROG_TYPE_LWT_IN **and **BPF_PROG_TYPE_LWT_XMIT**. A call to this helper is susceptible to change the underlying packet buffer. Therefore, at load time, all checks on pointers previously done by the verifier are invalidated and must be performed again, if the helper is used in combina‐ tion with direct packet access. **Return **0 on success, or a negative error in case of failure. **long bpf_lwt_seg6_store_bytes(struct sk_buff *_**skb_**, u32 _**offset_**, const void *_**from_**, u32 _**len_**)** **Description** Store _len_ bytes from address _from_ into the packet associated to _skb_, at _offset_. Only the flags, tag and TLVs inside the outermost IPv6 Segment Routing Header can be modified through this helper. A call to this helper is susceptible to change the underlying packet buffer. Therefore, at load time, all checks on pointers previously done by the verifier are invalidated and must be performed again, if the helper is used in combina‐ tion with direct packet access. **Return **0 on success, or a negative error in case of failure. **long bpf_lwt_seg6_adjust_srh(struct sk_buff *_**skb_**, u32 _**offset_**, s32 _**delta_**)** **Description** Adjust the size allocated to TLVs in the outermost IPv6 Segment Routing Header contained in the packet associated to _skb_, at position _offset_ by _delta_ bytes. Only offsets after the segments are accepted. _delta_ can be as well positive (growing) as negative (shrinking). A call to this helper is susceptible to change the underlying packet buffer. Therefore, at load time, all checks on pointers previously done by the verifier are invalidated and must be performed again, if the helper is used in combina‐ tion with direct packet access. **Return **0 on success, or a negative error in case of failure. **long bpf_lwt_seg6_action(struct sk_buff *_**skb_**, u32 _**action_**, void *_**param_**, u32 _**param_len_**)** **Description** Apply an IPv6 Segment Routing action of type _action_ to the packet associated to _skb_. Each action takes a parameter contained at address _param_, and of length _param_len_ bytes. _action_ can be one of: **SEG6_LOCAL_ACTION_END_X** End.X action: Endpoint with Layer-3 cross-connect. Type of _param_: **struct in6_addr**. **SEG6_LOCAL_ACTION_END_T** End.T action: Endpoint with specific IPv6 table lookup. Type of _param_: **int**. **SEG6_LOCAL_ACTION_END_B6** End.B6 action: Endpoint bound to an SRv6 policy. Type of _param_: **struct** **ipv6_sr_hdr**. **SEG6_LOCAL_ACTION_END_B6_ENCAP** End.B6.Encap action: Endpoint bound to an SRv6 encapsulation policy. Type of _param_: **struct ipv6_sr_hdr**. A call to this helper is susceptible to change the underlying packet buffer. Therefore, at load time, all checks on pointers previously done by the verifier are invalidated and must be performed again, if the helper is used in combina‐ tion with direct packet access. **Return **0 on success, or a negative error in case of failure. **long bpf_rc_repeat(void *_**ctx_**)** **Description** This helper is used in programs implementing IR decoding, to report a success‐ fully decoded repeat key message. This delays the generation of a key up event for previously generated key down event. Some IR protocols like NEC have a special IR message for repeating last button, for when a button is held down. The _ctx_ should point to the lirc sample as passed into the program. This helper is only available is the kernel was compiled with the **CON‐** **FIG_BPF_LIRC_MODE2 **configuration option set to "**y**". **Return **0 **long bpf_rc_keydown(void *_**ctx_**, u32 _**protocol_**, u64 _**scancode_**, u32 _**toggle_**)** **Description** This helper is used in programs implementing IR decoding, to report a success‐ fully decoded key press with _scancode_, _toggle_ value in the given _protocol_. The scancode will be translated to a keycode using the rc keymap, and reported as an input key down event. After a period a key up event is generated. This pe‐ riod can be extended by calling either **bpf_rc_keydown**() again with the same values, or calling **bpf_rc_repeat**(). Some protocols include a toggle bit, in case the button was released and pressed again between consecutive scancodes. The _ctx_ should point to the lirc sample as passed into the program. The _protocol_ is the decoded protocol number (see **enum rc_proto **for some prede‐ fined values). This helper is only available is the kernel was compiled with the **CON‐** **FIG_BPF_LIRC_MODE2 **configuration option set to "**y**". **Return **0 **u64 bpf_skb_cgroup_id(struct sk_buff *_**skb_**)** **Description** Return the cgroup v2 id of the socket associated with the _skb_. This is roughly similar to the **bpf_get_cgroup_classid**() helper for cgroup v1 by providing a tag resp. identifier that can be matched on or used for map lookups e.g. to imple‐ ment policy. The cgroup v2 id of a given path in the hierarchy is exposed in user space through the f_handle API in order to get to the same 64-bit id. This helper can be used on TC egress path, but not on ingress, and is available only if the kernel was compiled with the **CONFIG_SOCK_CGROUP_DATA **configuration option. **Return **The id is returned or 0 in case the id could not be retrieved. ### u64 bpf_get_current_cgroup_id(void) **Description** Get the current cgroup id based on the cgroup within which the current task is running. **Return **A 64-bit integer containing the current cgroup id based on the cgroup within which the current task is running. **void *bpf_get_local_storage(void *_**map_**, u64 _**flags_**)** **Description** Get the pointer to the local storage area. The type and the size of the local storage is defined by the _map_ argument. The _flags_ meaning is specific for each map type, and has to be 0 for cgroup local storage. Depending on the BPF program type, a local storage area can be shared between multiple instances of the BPF program, running simultaneously. A user should care about the synchronization by himself. For example, by using the **BPF_ATOMIC **instructions to alter the shared data. **Return **A pointer to the local storage area. **long bpf_sk_select_reuseport(struct sk_reuseport_md *_**reuse_**, struct bpf_map *_**map_**, void *_**key_**,** **u64 _**flags_**)** **Description** Select a **SO_REUSEPORT **socket from a **BPF_MAP_TYPE_REUSEPORT_SOCKARRAY _**map_. It checks the selected socket is matching the incoming request in the socket buffer. **Return **0 on success, or a negative error in case of failure. **u64 bpf_skb_ancestor_cgroup_id(struct sk_buff *_**skb_**, int _**ancestor_level_**)** **Description** Return id of cgroup v2 that is ancestor of cgroup associated with the _skb_ at the _ancestor_level_. The root cgroup is at _ancestor_level_ zero and each step down the hierarchy increments the level. If _ancestor_level_ == level of cgroup associated with _skb_, then return value will be same as that of **bpf_skb_cgroup_id**(). The helper is useful to implement policies based on cgroups that are upper in hierarchy than immediate cgroup associated with _skb_. The format of returned id and helper limitations are same as in **bpf_skb_cgroup_id**(). **Return **The id is returned or 0 in case the id could not be retrieved. **struct bpf_sock *bpf_sk_lookup_tcp(void *_**ctx_**, struct bpf_sock_tuple *_**tuple_**, u32 _**tuple_size_**,** **u64 _**netns_**, u64 _**flags_**)** **Description** Look for TCP socket matching _tuple_, optionally in a child network namespace _netns_. The return value must be checked, and if non-**NULL**, released via **bpf_sk_release**(). The _ctx_ should point to the context of the program, such as the skb or socket (depending on the hook in use). This is used to determine the base network namespace for the lookup. _tuple_size_ must be one of: **sizeof(_**tuple_**->ipv4)** Look for an IPv4 socket. **sizeof(_**tuple_**->ipv6)** Look for an IPv6 socket. If the _netns_ is a negative signed 32-bit integer, then the socket lookup table in the netns associated with the _ctx_ will be used. For the TC hooks, this is the netns of the device in the skb. For socket hooks, this is the netns of the socket. If _netns_ is any other signed 32-bit value greater than or equal to zero then it specifies the ID of the netns relative to the netns associated with the _ctx_. _netns_ values beyond the range of 32-bit integers are reserved for future use. All values for _flags_ are reserved for future usage, and must be left at zero. This helper is available only if the kernel was compiled with **CONFIG_NET **con‐ figuration option. **Return **Pointer to **struct bpf_sock**, or **NULL **in case of failure. For sockets with reuseport option, the **struct bpf_sock **result is from _reuse_**->socks**[] using the hash of the tuple. **struct bpf_sock *bpf_sk_lookup_udp(void *_**ctx_**, struct bpf_sock_tuple *_**tuple_**, u32 _**tuple_size_**,** **u64 _**netns_**, u64 _**flags_**)** **Description** Look for UDP socket matching _tuple_, optionally in a child network namespace _netns_. The return value must be checked, and if non-**NULL**, released via **bpf_sk_release**(). The _ctx_ should point to the context of the program, such as the skb or socket (depending on the hook in use). This is used to determine the base network namespace for the lookup. _tuple_size_ must be one of: **sizeof(_**tuple_**->ipv4)** Look for an IPv4 socket. **sizeof(_**tuple_**->ipv6)** Look for an IPv6 socket. If the _netns_ is a negative signed 32-bit integer, then the socket lookup table in the netns associated with the _ctx_ will be used. For the TC hooks, this is the netns of the device in the skb. For socket hooks, this is the netns of the socket. If _netns_ is any other signed 32-bit value greater than or equal to zero then it specifies the ID of the netns relative to the netns associated with the _ctx_. _netns_ values beyond the range of 32-bit integers are reserved for future use. All values for _flags_ are reserved for future usage, and must be left at zero. This helper is available only if the kernel was compiled with **CONFIG_NET **con‐ figuration option. **Return **Pointer to **struct bpf_sock**, or **NULL **in case of failure. For sockets with reuseport option, the **struct bpf_sock **result is from _reuse_**->socks**[] using the hash of the tuple. **long bpf_sk_release(void *_**sock_**)** **Description** Release the reference held by _sock_. _sock_ must be a non-**NULL **pointer that was returned from **bpf_sk_lookup_xxx**(). **Return **0 on success, or a negative error in case of failure. **long bpf_map_push_elem(struct bpf_map *_**map_**, const void *_**value_**, u64 _**flags_**)** **Description** Push an element _value_ in _map_. _flags_ is one of: **BPF_EXIST** If the queue/stack is full, the oldest element is removed to make room for this. **Return **0 on success, or a negative error in case of failure. **long bpf_map_pop_elem(struct bpf_map *_**map_**, void *_**value_**)** **Description** Pop an element from _map_. **Return **0 on success, or a negative error in case of failure. **long bpf_map_peek_elem(struct bpf_map *_**map_**, void *_**value_**)** **Description** Get an element from _map_ without removing it. **Return **0 on success, or a negative error in case of failure. **long bpf_msg_push_data(struct sk_msg_buff *_**msg_**, u32 _**start_**, u32 _**len_**, u64 _**flags_**)** **Description** For socket policies, insert _len_ bytes into _msg_ at offset _start_. If a program of type **BPF_PROG_TYPE_SK_MSG **is run on a _msg_ it may want to insert metadata or options into the _msg_. This can later be read and used by any of the lower layer BPF hooks. This helper may fail if under memory pressure (a malloc fails) in these cases BPF programs will get an appropriate error and BPF programs will need to handle them. **Return **0 on success, or a negative error in case of failure. **long bpf_msg_pop_data(struct sk_msg_buff *_**msg_**, u32 _**start_**, u32 _**len_**, u64 _**flags_**)** **Description** Will remove _len_ bytes from a _msg_ starting at byte _start_. This may result in **ENOMEM **errors under certain situations if an allocation and copy are required due to a full ring buffer. However, the helper will try to avoid doing the al‐ location if possible. Other errors can occur if input parameters are invalid either due to _start_ byte not being valid part of _msg_ payload and/or _pop_ value being to large. **Return **0 on success, or a negative error in case of failure. **long bpf_rc_pointer_rel(void *_**ctx_**, s32 _**rel_x_**, s32 _**rel_y_**)** **Description** This helper is used in programs implementing IR decoding, to report a success‐ fully decoded pointer movement. The _ctx_ should point to the lirc sample as passed into the program. This helper is only available is the kernel was compiled with the **CON‐** **FIG_BPF_LIRC_MODE2 **configuration option set to "**y**". **Return **0 **long bpf_spin_lock(struct bpf_spin_lock *_**lock_**)** **Description** Acquire a spinlock represented by the pointer _lock_, which is stored as part of a value of a map. Taking the lock allows to safely update the rest of the fields in that value. The spinlock can (and must) later be released with a call to **bpf_spin_unlock**(_lock_). Spinlocks in BPF programs come with a number of restrictions and constraints: • **bpf_spin_lock **objects are only allowed inside maps of types **BPF_MAP_TYPE_HASH** and **BPF_MAP_TYPE_ARRAY **(this list could be extended in the future). • BTF description of the map is mandatory. • The BPF program can take ONE lock at a time, since taking two or more could cause dead locks. • Only one **struct bpf_spin_lock **is allowed per map element. • When the lock is taken, calls (either BPF to BPF or helpers) are not allowed. • The **BPF_LD_ABS **and **BPF_LD_IND **instructions are not allowed inside a spin‐ lock-ed region. • The BPF program MUST call **bpf_spin_unlock**() to release the lock, on all exe‐ cution paths, before it returns. • The BPF program can access **struct bpf_spin_lock **only via the **bpf_spin_lock**() and **bpf_spin_unlock**() helpers. Loading or storing data into the **struct** **bpf_spin_lock _**lock_**; **field of a map is not allowed. • To use the **bpf_spin_lock**() helper, the BTF description of the map value must be a struct and have **struct bpf_spin_lock _**anyname_**; **field at the top level. Nested lock inside another struct is not allowed. • The **struct bpf_spin_lock _**lock_ field in a map value must be aligned on a mul‐ tiple of 4 bytes in that value. • Syscall with command **BPF_MAP_LOOKUP_ELEM **does not copy the **bpf_spin_lock** field to user space. • Syscall with command **BPF_MAP_UPDATE_ELEM**, or update from a BPF program, do not update the **bpf_spin_lock **field. • **bpf_spin_lock **cannot be on the stack or inside a networking packet (it can only be inside of a map values). • **bpf_spin_lock **is available to root only. • Tracing programs and socket filter programs cannot use **bpf_spin_lock**() due to insufficient preemption checks (but this may change in the future). • **bpf_spin_lock **is not allowed in inner maps of map-in-map. **Return **0 **long bpf_spin_unlock(struct bpf_spin_lock *_**lock_**)** **Description** Release the _lock_ previously locked by a call to **bpf_spin_lock**(_lock_). **Return **0 **struct bpf_sock *bpf_sk_fullsock(struct bpf_sock *_**sk_**)** **Description** This helper gets a **struct bpf_sock **pointer such that all the fields in this **bpf_sock **can be accessed. **Return **A **struct bpf_sock **pointer on success, or **NULL **in case of failure. **struct bpf_tcp_sock *bpf_tcp_sock(struct bpf_sock *_**sk_**)** **Description** This helper gets a **struct bpf_tcp_sock **pointer from a **struct bpf_sock **pointer. **Return **A **struct bpf_tcp_sock **pointer on success, or **NULL **in case of failure. **long bpf_skb_ecn_set_ce(struct sk_buff *_**skb_**)** **Description** Set ECN (Explicit Congestion Notification) field of IP header to **CE **(Congestion Encountered) if current value is **ECT **(ECN Capable Transport). Otherwise, do nothing. Works with IPv6 and IPv4. **Return **1 if the **CE **flag is set (either by the current helper call or because it was already present), 0 if it is not set. **struct bpf_sock *bpf_get_listener_sock(struct bpf_sock *_**sk_**)** **Description** Return a **struct bpf_sock **pointer in **TCP_LISTEN **state. **bpf_sk_release**() is un‐ necessary and not allowed. **Return **A **struct bpf_sock **pointer on success, or **NULL **in case of failure. **struct bpf_sock *bpf_skc_lookup_tcp(void *_**ctx_**, struct bpf_sock_tuple *_**tuple_**, u32 _**tuple_size_**,** **u64 _**netns_**, u64 _**flags_**)** **Description** Look for TCP socket matching _tuple_, optionally in a child network namespace _netns_. The return value must be checked, and if non-**NULL**, released via **bpf_sk_release**(). This function is identical to **bpf_sk_lookup_tcp**(), except that it also returns timewait or request sockets. Use **bpf_sk_fullsock**() or **bpf_tcp_sock**() to access the full structure. This helper is available only if the kernel was compiled with **CONFIG_NET **con‐ figuration option. **Return **Pointer to **struct bpf_sock**, or **NULL **in case of failure. For sockets with reuseport option, the **struct bpf_sock **result is from _reuse_**->socks**[] using the hash of the tuple. **long bpf_tcp_check_syncookie(void *_**sk_**, void *_**iph_**, u32 _**iph_len_**, struct tcphdr *_**th_**, u32 _**th_len_**)** **Description** Check whether _iph_ and _th_ contain a valid SYN cookie ACK for the listening socket in _sk_. _iph_ points to the start of the IPv4 or IPv6 header, while _iph_len_ contains **sizeof**(**struct iphdr**) or **sizeof**(**struct ipv6hdr**). _th_ points to the start of the TCP header, while _th_len_ contains the length of the TCP header (at least **sizeof**(**struct tcphdr**)). **Return **0 if _iph_ and _th_ are a valid SYN cookie ACK, or a negative error otherwise. **long bpf_sysctl_get_name(struct bpf_sysctl *_**ctx_**, char *_**buf_**, size_t _**buf_len_**, u64 _**flags_**)** **Description** Get name of sysctl in /proc/sys/ and copy it into provided by program buffer _buf_ of size _buf_len_. The buffer is always NUL terminated, unless it's zero-sized. If _flags_ is zero, full name (e.g. "net/ipv4/tcp_mem") is copied. Use **BPF_F_SYSCTL_BASE_NAME **flag to copy base name only (e.g. "tcp_mem"). **Return **Number of character copied (not including the trailing NUL). **-E2BIG **if the buffer wasn't big enough (_buf_ will contain truncated name in this case). **long bpf_sysctl_get_current_value(struct bpf_sysctl *_**ctx_**, char *_**buf_**, size_t _**buf_len_**)** **Description** Get current value of sysctl as it is presented in /proc/sys (incl. newline, etc), and copy it as a string into provided by program buffer _buf_ of size _buf_len_. The whole value is copied, no matter what file position user space issued e.g. sys_read at. The buffer is always NUL terminated, unless it's zero-sized. **Return **Number of character copied (not including the trailing NUL). **-E2BIG **if the buffer wasn't big enough (_buf_ will contain truncated name in this case). **-EINVAL **if current value was unavailable, e.g. because sysctl is uninitialized and read returns -EIO for it. **long bpf_sysctl_get_new_value(struct bpf_sysctl *_**ctx_**, char *_**buf_**, size_t _**buf_len_**)** **Description** Get new value being written by user space to sysctl (before the actual write happens) and copy it as a string into provided by program buffer _buf_ of size _buf_len_. User space may write new value at file position > 0. The buffer is always NUL terminated, unless it's zero-sized. **Return **Number of character copied (not including the trailing NUL). **-E2BIG **if the buffer wasn't big enough (_buf_ will contain truncated name in this case). **-EINVAL **if sysctl is being read. **long bpf_sysctl_set_new_value(struct bpf_sysctl *_**ctx_**, const char *_**buf_**, size_t _**buf_len_**)** **Description** Override new value being written by user space to sysctl with value provided by program in buffer _buf_ of size _buf_len_. _buf_ should contain a string in same form as provided by user space on sysctl write. User space may write new value at file position > 0. To override the whole sysctl value file position should be set to zero. **Return **0 on success. **-E2BIG **if the _buf_len_ is too big. **-EINVAL **if sysctl is being read. **long bpf_strtol(const char *_**buf_**, size_t _**buf_len_**, u64 _**flags_**, long *_**res_**)** **Description** Convert the initial part of the string from buffer _buf_ of size _buf_len_ to a long integer according to the given base and save the result in _res_. The string may begin with an arbitrary amount of white space (as determined by [**isspace**(3)](https://www.chedong.com/phpMan.php/man/isspace/3/markdown)) followed by a single optional '**-**' sign. Five least significant bits of _flags_ encode base, other bits are currently un‐ used. Base must be either 8, 10, 16 or 0 to detect it automatically similar to user space [**strtol**(3)](https://www.chedong.com/phpMan.php/man/strtol/3/markdown). **Return **Number of characters consumed on success. Must be positive but no more than _buf_len_. **-EINVAL **if no valid digits were found or unsupported base was provided. **-ERANGE **if resulting value was out of range. **long bpf_strtoul(const char *_**buf_**, size_t _**buf_len_**, u64 _**flags_**, unsigned long *_**res_**)** **Description** Convert the initial part of the string from buffer _buf_ of size _buf_len_ to an unsigned long integer according to the given base and save the result in _res_. The string may begin with an arbitrary amount of white space (as determined by [**isspace**(3)](https://www.chedong.com/phpMan.php/man/isspace/3/markdown)). Five least significant bits of _flags_ encode base, other bits are currently un‐ used. Base must be either 8, 10, 16 or 0 to detect it automatically similar to user space [**strtoul**(3)](https://www.chedong.com/phpMan.php/man/strtoul/3/markdown). **Return **Number of characters consumed on success. Must be positive but no more than _buf_len_. **-EINVAL **if no valid digits were found or unsupported base was provided. **-ERANGE **if resulting value was out of range. **void *bpf_sk_storage_get(struct bpf_map *_**map_**, void *_**sk_**, void *_**value_**, u64 _**flags_**)** **Description** Get a bpf-local-storage from a _sk_. Logically, it could be thought of getting the value from a _map_ with _sk_ as the **key**. From this perspective, the usage is not much different from **bpf_map_lookup_elem**(_map_, **&_**sk_) except this helper enforces the key must be a full socket and the map must be a **BPF_MAP_TYPE_SK_STORAGE **also. Underneath, the value is stored locally at _sk_ instead of the _map_. The _map_ is used as the bpf-local-storage "type". The bpf-local-storage "type" (i.e. the _map_) is searched against all bpf-local-storages residing at _sk_. _sk_ is a kernel **struct sock **pointer for LSM program. _sk_ is a **struct bpf_sock** pointer for other program types. An optional _flags_ (**BPF_SK_STORAGE_GET_F_CREATE**) can be used such that a new bpf-local-storage will be created if one does not exist. _value_ can be used to‐ gether with **BPF_SK_STORAGE_GET_F_CREATE **to specify the initial value of a bpf-local-storage. If _value_ is **NULL**, the new bpf-local-storage will be zero initialized. **Return **A bpf-local-storage pointer is returned on success. **NULL **if not found or there was an error in adding a new bpf-local-storage. **long bpf_sk_storage_delete(struct bpf_map *_**map_**, void *_**sk_**)** **Description** Delete a bpf-local-storage from a _sk_. **Return **0 on success. **-ENOENT **if the bpf-local-storage cannot be found. **-EINVAL **if sk is not a full‐ sock (e.g. a request_sock). **long bpf_send_signal(u32 _**sig_**)** **Description** Send signal _sig_ to the process of the current task. The signal may be deliv‐ ered to any of this process's threads. **Return **0 on success or successfully queued. **-EBUSY **if work queue under nmi is full. **-EINVAL **if _sig_ is invalid. **-EPERM **if no permission to send the _sig_. **-EAGAIN **if bpf program can try again. **s64 bpf_tcp_gen_syncookie(void *_**sk_**, void *_**iph_**, u32 _**iph_len_**, struct tcphdr *_**th_**, u32 _**th_len_**)** **Description** Try to issue a SYN cookie for the packet with corresponding IP/TCP headers, _iph_ and _th_, on the listening socket in _sk_. _iph_ points to the start of the IPv4 or IPv6 header, while _iph_len_ contains **sizeof**(**struct iphdr**) or **sizeof**(**struct ipv6hdr**). _th_ points to the start of the TCP header, while _th_len_ contains the length of the TCP header with options (at least **sizeof**(**struct tcphdr**)). **Return **On success, lower 32 bits hold the generated SYN cookie in followed by 16 bits which hold the MSS value for that cookie, and the top 16 bits are unused. On failure, the returned value is one of the following: **-EINVAL **SYN cookie cannot be issued due to error **-ENOENT **SYN cookie should not be issued (no SYN flood) **-EOPNOTSUPP **kernel configuration does not enable SYN cookies **-EPROTONOSUPPORT **IP packet version is not 4 or 6 **long bpf_skb_output(void *_**ctx_**, struct bpf_map *_**map_**, u64 _**flags_**, void *_**data_**, u64 _**size_**)** **Description** Write raw _data_ blob into a special BPF perf event held by _map_ of type **BPF_MAP_TYPE_PERF_EVENT_ARRAY**. This perf event must have the following attrib‐ utes: **PERF_SAMPLE_RAW **as **sample_type**, **PERF_TYPE_SOFTWARE **as **type**, and **PERF_COUNT_SW_BPF_OUTPUT **as **config**. The _flags_ are used to indicate the index in _map_ for which the value must be put, masked with **BPF_F_INDEX_MASK**. Alternatively, _flags_ can be set to **BPF_F_CURRENT_CPU **to indicate that the index of the current CPU core should be used. The value to write, of _size_, is passed through eBPF stack and pointed by _data_. _ctx_ is a pointer to in-kernel struct sk_buff. This helper is similar to **bpf_perf_event_output**() but restricted to raw_trace‐ point bpf programs. **Return **0 on success, or a negative error in case of failure. **long bpf_probe_read_user(void *_**dst_**, u32 _**size_**, const void *_**unsafe_ptr_**)** **Description** Safely attempt to read _size_ bytes from user space address _unsafe_ptr_ and store the data in _dst_. **Return **0 on success, or a negative error in case of failure. **long bpf_probe_read_kernel(void *_**dst_**, u32 _**size_**, const void *_**unsafe_ptr_**)** **Description** Safely attempt to read _size_ bytes from kernel space address _unsafe_ptr_ and store the data in _dst_. **Return **0 on success, or a negative error in case of failure. **long bpf_probe_read_user_str(void *_**dst_**, u32 _**size_**, const void *_**unsafe_ptr_**)** **Description** Copy a NUL terminated string from an unsafe user address _unsafe_ptr_ to _dst_. The _size_ should include the terminating NUL byte. In case the string length is smaller than _size_, the target is not padded with further NUL bytes. If the string length is larger than _size_, just _size_-1 bytes are copied and the last byte is set to NUL. On success, returns the number of bytes that were written, including the termi‐ nal NUL. This makes this helper useful in tracing programs for reading strings, and more importantly to get its length at runtime. See the following snippet: SEC("kprobe/sys_open") void bpf_sys_open(struct pt_regs *ctx) { char buf[PATHLEN]; // PATHLEN is defined to 256 int res = bpf_probe_read_user_str(buf, sizeof(buf), ctx->di); // Consume buf, for example push it to // userspace via bpf_perf_event_output(); we // can use res (the string length) as event // size, after checking its boundaries. } In comparison, using **bpf_probe_read_user**() helper here instead to read the string would require to estimate the length at compile time, and would often result in copying more memory than necessary. Another useful use case is when parsing individual process arguments or indi‐ vidual environment variables navigating _current_**->mm->arg_start **and _cur‐_ _rent_**->mm->env_start**: using this helper and the return value, one can quickly iterate at the right offset of the memory area. **Return **On success, the strictly positive length of the output string, including the trailing NUL character. On error, a negative value. **long bpf_probe_read_kernel_str(void *_**dst_**, u32 _**size_**, const void *_**unsafe_ptr_**)** **Description** Copy a NUL terminated string from an unsafe kernel address _unsafe_ptr_ to _dst_. Same semantics as with **bpf_probe_read_user_str**() apply. **Return **On success, the strictly positive length of the string, including the trailing NUL character. On error, a negative value. **long bpf_tcp_send_ack(void *_**tp_**, u32 _**rcv_nxt_**)** **Description** Send out a tcp-ack. _tp_ is the in-kernel struct **tcp_sock**. _rcv_nxt_ is the ack_seq to be sent out. **Return **0 on success, or a negative error in case of failure. **long bpf_send_signal_thread(u32 _**sig_**)** **Description** Send signal _sig_ to the thread corresponding to the current task. **Return **0 on success or successfully queued. **-EBUSY **if work queue under nmi is full. **-EINVAL **if _sig_ is invalid. **-EPERM **if no permission to send the _sig_. **-EAGAIN **if bpf program can try again. ### u64 bpf_jiffies64(void) **Description** Obtain the 64bit jiffies **Return **The 64 bit jiffies **long bpf_read_branch_records(struct bpf_perf_event_data *_**ctx_**, void *_**buf_**, u32 _**size_**, u64 _**flags_**)** **Description** For an eBPF program attached to a perf event, retrieve the branch records (**struct perf_branch_entry**) associated to _ctx_ and store it in the buffer pointed by _buf_ up to size _size_ bytes. **Return **On success, number of bytes written to _buf_. On error, a negative value. The _flags_ can be set to **BPF_F_GET_BRANCH_RECORDS_SIZE **to instead return the number of bytes required to store all the branch entries. If this flag is set, _buf_ may be NULL. **-EINVAL **if arguments invalid or **size **not a multiple of **sizeof**(**struct** **perf_branch_entry**). **-ENOENT **if architecture does not support branch records. **long bpf_get_ns_current_pid_tgid(u64 _**dev_**, u64 _**ino_**, struct bpf_pidns_info *_**nsdata_**, u32 _**size_**)** **Description** Returns 0 on success, values for _pid_ and _tgid_ as seen from the current _name‐_ _space_ will be returned in _nsdata_. **Return **0 on success, or one of the following in case of failure: **-EINVAL **if dev and inum supplied don't match dev_t and inode number with nsfs of current task, or if dev conversion to dev_t lost high bits. **-ENOENT **if pidns does not exists for the current task. **long bpf_xdp_output(void *_**ctx_**, struct bpf_map *_**map_**, u64 _**flags_**, void *_**data_**, u64 _**size_**)** **Description** Write raw _data_ blob into a special BPF perf event held by _map_ of type **BPF_MAP_TYPE_PERF_EVENT_ARRAY**. This perf event must have the following attrib‐ utes: **PERF_SAMPLE_RAW **as **sample_type**, **PERF_TYPE_SOFTWARE **as **type**, and **PERF_COUNT_SW_BPF_OUTPUT **as **config**. The _flags_ are used to indicate the index in _map_ for which the value must be put, masked with **BPF_F_INDEX_MASK**. Alternatively, _flags_ can be set to **BPF_F_CURRENT_CPU **to indicate that the index of the current CPU core should be used. The value to write, of _size_, is passed through eBPF stack and pointed by _data_. _ctx_ is a pointer to in-kernel struct xdp_buff. This helper is similar to **bpf_perf_eventoutput**() but restricted to raw_trace‐ point bpf programs. **Return **0 on success, or a negative error in case of failure. **u64 bpf_get_netns_cookie(void *_**ctx_**)** **Description** Retrieve the cookie (generated by the kernel) of the network namespace the in‐ put _ctx_ is associated with. The network namespace cookie remains stable for its lifetime and provides a global identifier that can be assumed unique. If _ctx_ is NULL, then the helper returns the cookie for the initial network namespace. The cookie itself is very similar to that of **bpf_get_socket_cookie**() helper, but for network namespaces instead of sockets. **Return **A 8-byte long opaque number. **u64 bpf_get_current_ancestor_cgroup_id(int _**ancestor_level_**)** **Description** Return id of cgroup v2 that is ancestor of the cgroup associated with the cur‐ rent task at the _ancestor_level_. The root cgroup is at _ancestor_level_ zero and each step down the hierarchy increments the level. If _ancestor_level_ == level of cgroup associated with the current task, then return value will be the same as that of **bpf_get_current_cgroup_id**(). The helper is useful to implement policies based on cgroups that are upper in hierarchy than immediate cgroup associated with the current task. The format of returned id and helper limitations are same as in **bpf_get_cur‐** **rent_cgroup_id**(). **Return **The id is returned or 0 in case the id could not be retrieved. **long bpf_sk_assign(struct sk_buff *_**skb_**, void *_**sk_**, u64 _**flags_**)** **Description** Helper is overloaded depending on BPF program type. This description applies to **BPF_PROG_TYPE_SCHED_CLS **and **BPF_PROG_TYPE_SCHED_ACT **programs. Assign the _sk_ to the _skb_. When combined with appropriate routing configuration to receive the packet towards the socket, will cause _skb_ to be delivered to the specified socket. Subsequent redirection of _skb_ via **bpf_redirect**(), **bpf_clone_redirect**() or other methods outside of BPF may interfere with suc‐ cessful delivery to the socket. This operation is only valid from TC ingress path. The _flags_ argument must be zero. **Return **0 on success, or a negative error in case of failure: **-EINVAL **if specified _flags_ are not supported. **-ENOENT **if the socket is unavailable for assignment. **-ENETUNREACH **if the socket is unreachable (wrong netns). **-EOPNOTSUPP **if the operation is not supported, for example a call from outside of TC ingress. **long bpf_sk_assign(struct bpf_sk_lookup *_**ctx_**, struct bpf_sock *_**sk_**, u64 _**flags_**)** **Description** Helper is overloaded depending on BPF program type. This description applies to **BPF_PROG_TYPE_SK_LOOKUP **programs. Select the _sk_ as a result of a socket lookup. For the operation to succeed passed socket must be compatible with the packet description provided by the _ctx_ object. L4 protocol (**IPPROTO_TCP **or **IPPROTO_UDP**) must be an exact match. While IP fam‐ ily (**AF_INET **or **AF_INET6**) must be compatible, that is IPv6 sockets that are not v6-only can be selected for IPv4 packets. Only TCP listeners and UDP unconnected sockets can be selected. _sk_ can also be NULL to reset any previous selection. _flags_ argument can combination of following values: • **BPF_SK_LOOKUP_F_REPLACE **to override the previous socket selection, poten‐ tially done by a BPF program that ran before us. • **BPF_SK_LOOKUP_F_NO_REUSEPORT **to skip load-balancing within reuseport group for the socket being selected. On success _ctx->sk_ will point to the selected socket. **Return **0 on success, or a negative errno in case of failure. • **-EAFNOSUPPORT **if socket family (_sk->family_) is not compatible with packet family (_ctx->family_). • **-EEXIST **if socket has been already selected, potentially by another program, and **BPF_SK_LOOKUP_F_REPLACE **flag was not specified. • **-EINVAL **if unsupported flags were specified. • **-EPROTOTYPE **if socket L4 protocol (_sk->protocol_) doesn't match packet proto‐ col (_ctx->protocol_). • **-ESOCKTNOSUPPORT **if socket is not in allowed state (TCP listening or UDP un‐ connected). ### u64 bpf_ktime_get_boot_ns(void) **Description** Return the time elapsed since system boot, in nanoseconds. Does include the time the system was suspended. See: **clock_gettime**(**CLOCK_BOOTTIME**) **Return **Current _ktime_. **long bpf_seq_printf(struct seq_file *_**m_**, const char *_**fmt_**, u32 _**fmt_size_**, const void *_**data_**, u32** _data_len_**)** **Description** **bpf_seq_printf**() uses seq_file **seq_printf**() to print out the format string. The _m_ represents the seq_file. The _fmt_ and _fmt_size_ are for the format string itself. The _data_ and _data_len_ are format string arguments. The _data_ are a **u64** array and corresponding format string values are stored in the array. For strings and pointers where pointees are accessed, only the pointer values are stored in the _data_ array. The _data_len_ is the size of _data_ in bytes - must be a multiple of 8. Formats **%s**, **%p{i,I}{4,6} **requires to read kernel memory. Reading kernel memory may fail due to either invalid address or valid address but requiring a major memory fault. If reading kernel memory fails, the string for **%s **will be an empty string, and the ip address for **%p{i,I}{4,6} **will be 0. Not returning er‐ ror to bpf program is consistent with what **bpf_trace_printk**() does for now. **Return **0 on success, or a negative error in case of failure: **-EBUSY **if per-CPU memory copy buffer is busy, can try again by returning 1 from bpf program. **-EINVAL **if arguments are invalid, or if _fmt_ is invalid/unsupported. **-E2BIG **if _fmt_ contains too many format specifiers. **-EOVERFLOW **if an overflow happened: The same object will be tried again. **long bpf_seq_write(struct seq_file *_**m_**, const void *_**data_**, u32 _**len_**)** **Description** **bpf_seq_write**() uses seq_file **seq_write**() to write the data. The _m_ represents the seq_file. The _data_ and _len_ represent the data to write in bytes. **Return **0 on success, or a negative error in case of failure: **-EOVERFLOW **if an overflow happened: The same object will be tried again. **u64 bpf_sk_cgroup_id(void *_**sk_**)** **Description** Return the cgroup v2 id of the socket _sk_. _sk_ must be a non-**NULL **pointer to a socket, e.g. one returned from **bpf_sk_lookup_xxx**(), **bpf_sk_fullsock**(), etc. The format of returned id is same as in **bpf_skb_cgroup_id**(). This helper is available only if the kernel was compiled with the **CON‐** **FIG_SOCK_CGROUP_DATA **configuration option. **Return **The id is returned or 0 in case the id could not be retrieved. **u64 bpf_sk_ancestor_cgroup_id(void *_**sk_**, int _**ancestor_level_**)** **Description** Return id of cgroup v2 that is ancestor of cgroup associated with the _sk_ at the _ancestor_level_. The root cgroup is at _ancestor_level_ zero and each step down the hierarchy increments the level. If _ancestor_level_ == level of cgroup asso‐ ciated with _sk_, then return value will be same as that of **bpf_sk_cgroup_id**(). The helper is useful to implement policies based on cgroups that are upper in hierarchy than immediate cgroup associated with _sk_. The format of returned id and helper limitations are same as in **bpf_sk_cgroup_id**(). **Return **The id is returned or 0 in case the id could not be retrieved. **long bpf_ringbuf_output(void *_**ringbuf_**, void *_**data_**, u64 _**size_**, u64 _**flags_**)** **Description** Copy _size_ bytes from _data_ into a ring buffer _ringbuf_. If **BPF_RB_NO_WAKEUP **is specified in _flags_, no notification of new data availability is sent. If **BPF_RB_FORCE_WAKEUP **is specified in _flags_, notification of new data availabil‐ ity is sent unconditionally. If **0 **is specified in _flags_, an adaptive notifica‐ tion of new data availability is sent. An adaptive notification is a notification sent whenever the user-space process has caught up and consumed all available payloads. In case the user-space process is still processing a previous payload, then no notification is needed as it will process the newly added payload automatically. **Return **0 on success, or a negative error in case of failure. **void *bpf_ringbuf_reserve(void *_**ringbuf_**, u64 _**size_**, u64 _**flags_**)** **Description** Reserve _size_ bytes of payload in a ring buffer _ringbuf_. _flags_ must be 0. **Return **Valid pointer with _size_ bytes of memory available; NULL, otherwise. **void bpf_ringbuf_submit(void *_**data_**, u64 _**flags_**)** **Description** Submit reserved ring buffer sample, pointed to by _data_. If **BPF_RB_NO_WAKEUP **is specified in _flags_, no notification of new data availability is sent. If **BPF_RB_FORCE_WAKEUP **is specified in _flags_, notification of new data availabil‐ ity is sent unconditionally. If **0 **is specified in _flags_, an adaptive notifica‐ tion of new data availability is sent. See 'bpf_ringbuf_output()' for the definition of adaptive notification. **Return **Nothing. Always succeeds. **void bpf_ringbuf_discard(void *_**data_**, u64 _**flags_**)** **Description** Discard reserved ring buffer sample, pointed to by _data_. If **BPF_RB_NO_WAKEUP** is specified in _flags_, no notification of new data availability is sent. If **BPF_RB_FORCE_WAKEUP **is specified in _flags_, notification of new data availabil‐ ity is sent unconditionally. If **0 **is specified in _flags_, an adaptive notifica‐ tion of new data availability is sent. See 'bpf_ringbuf_output()' for the definition of adaptive notification. **Return **Nothing. Always succeeds. **u64 bpf_ringbuf_query(void *_**ringbuf_**, u64 _**flags_**)** **Description** Query various characteristics of provided ring buffer. What exactly is queries is determined by _flags_: • **BPF_RB_AVAIL_DATA**: Amount of data not yet consumed. • **BPF_RB_RING_SIZE**: The size of ring buffer. • **BPF_RB_CONS_POS**: Consumer position (can wrap around). • **BPF_RB_PROD_POS**: Producer(s) position (can wrap around). Data returned is just a momentary snapshot of actual values and could be inac‐ curate, so this facility should be used to power heuristics and for reporting, not to make 100% correct calculation. **Return **Requested value, or 0, if _flags_ are not recognized. **long bpf_csum_level(struct sk_buff *_**skb_**, u64 _**level_**)** **Description** Change the skbs checksum level by one layer up or down, or reset it entirely to none in order to have the stack perform checksum validation. The level is ap‐ plicable to the following protocols: TCP, UDP, GRE, SCTP, FCOE. For example, a decap of | ETH | IP | UDP | GUE | IP | TCP | into | ETH | IP | TCP | through **bpf_skb_adjust_room**() helper with passing in **BPF_F_ADJ_ROOM_NO_CSUM_RESET **flag would require one call to **bpf_csum_level**() with **BPF_CSUM_LEVEL_DEC **since the UDP header is removed. Similarly, an encap of the latter into the former could be accompanied by a helper call to **bpf_csum_level**() with **BPF_CSUM_LEVEL_INC **if the skb is still intended to be processed in higher layers of the stack instead of just egressing at tc. There are three supported level settings at this time: • **BPF_CSUM_LEVEL_INC**: Increases skb->csum_level for skbs with CHECKSUM_UNNECES‐ SARY. • **BPF_CSUM_LEVEL_DEC**: Decreases skb->csum_level for skbs with CHECKSUM_UNNECES‐ SARY. • **BPF_CSUM_LEVEL_RESET**: Resets skb->csum_level to 0 and sets CHECKSUM_NONE to force checksum validation by the stack. • **BPF_CSUM_LEVEL_QUERY**: No-op, returns the current skb->csum_level. **Return **0 on success, or a negative error in case of failure. In the case of **BPF_CSUM_LEVEL_QUERY**, the current skb->csum_level is returned or the error code -EACCES in case the skb is not subject to CHECKSUM_UNNECESSARY. **struct tcp6_sock *bpf_skc_to_tcp6_sock(void *_**sk_**)** **Description** Dynamically cast a _sk_ pointer to a _tcp6_sock_ pointer. **Return _**sk_ if casting is valid, or **NULL **otherwise. **struct tcp_sock *bpf_skc_to_tcp_sock(void *_**sk_**)** **Description** Dynamically cast a _sk_ pointer to a _tcp_sock_ pointer. **Return _**sk_ if casting is valid, or **NULL **otherwise. **struct tcp_timewait_sock *bpf_skc_to_tcp_timewait_sock(void *_**sk_**)** **Description** Dynamically cast a _sk_ pointer to a _tcp_timewait_sock_ pointer. **Return _**sk_ if casting is valid, or **NULL **otherwise. **struct tcp_request_sock *bpf_skc_to_tcp_request_sock(void *_**sk_**)** **Description** Dynamically cast a _sk_ pointer to a _tcp_request_sock_ pointer. **Return _**sk_ if casting is valid, or **NULL **otherwise. **struct udp6_sock *bpf_skc_to_udp6_sock(void *_**sk_**)** **Description** Dynamically cast a _sk_ pointer to a _udp6_sock_ pointer. **Return _**sk_ if casting is valid, or **NULL **otherwise. **long bpf_get_task_stack(struct task_struct *_**task_**, void *_**buf_**, u32 _**size_**, u64 _**flags_**)** **Description** Return a user or a kernel stack in bpf program provided buffer. Note: the user stack will only be populated if the _task_ is the current task; all other tasks will return -EOPNOTSUPP. To achieve this, the helper needs _task_, which is a valid pointer to **struct task_struct**. To store the stacktrace, the bpf program provides _buf_ with a nonnegative _size_. The last argument, _flags_, holds the number of stack frames to skip (from 0 to 255), masked with **BPF_F_SKIP_FIELD_MASK**. The next bits can be used to set the following flags: **BPF_F_USER_STACK** Collect a user space stack instead of a kernel stack. The _task_ must be the current task. **BPF_F_USER_BUILD_ID** Collect buildid+offset instead of ips for user stack, only valid if **BPF_F_USER_STACK **is also specified. **bpf_get_task_stack**() can collect up to **PERF_MAX_STACK_DEPTH **both kernel and user frames, subject to sufficient large buffer size. Note that this limit can be controlled with the **sysctl **program, and that it should be manually increased in order to profile long user stacks (such as stacks for Java programs). To do so, use: # sysctl kernel.perf_event_max_stack= **Return **The non-negative copied _buf_ length equal to or less than _size_ on success, or a negative error in case of failure. **long bpf_load_hdr_opt(struct bpf_sock_ops *_**skops_**, void *_**searchby_res_**, u32 _**len_**, u64 _**flags_**)** **Description** Load header option. Support reading a particular TCP header option for bpf program (**BPF_PROG_TYPE_SOCK_OPS**). If _flags_ is 0, it will search the option from the _skops_**->skb_data**. The comment in **struct bpf_sock_ops **has details on what skb_data contains under different _skops_**->op**. The first byte of the _searchby_res_ specifies the kind that it wants to search. If the searching kind is an experimental kind (i.e. 253 or 254 according to RFC6994). It also needs to specify the "magic" which is either 2 bytes or 4 bytes. It then also needs to specify the size of the magic by using the 2nd byte which is "kind-length" of a TCP header option and the "kind-length" also includes the first 2 bytes "kind" and "kind-length" itself as a normal TCP header option also does. For example, to search experimental kind 254 with 2 byte magic 0xeB9F, the searchby_res should be [ 254, 4, 0xeB, 0x9F, 0, 0, .... 0 ]. To search for the standard window scale option (3), the _searchby_res_ should be [ 3, 0, 0, .... 0 ]. Note, kind-length must be 0 for regular option. Searching for No-Op (0) and End-of-Option-List (1) are not supported. _len_ must be at least 2 bytes which is the minimal size of a header option. Supported flags: • **BPF_LOAD_HDR_OPT_TCP_SYN **to search from the saved_syn packet or the just-re‐ ceived syn packet. **Return **> 0 when found, the header option is copied to _searchby_res_. The return value is the total length copied. On failure, a negative error code is returned: **-EINVAL **if a parameter is invalid. **-ENOMSG **if the option is not found. **-ENOENT **if no syn packet is available when **BPF_LOAD_HDR_OPT_TCP_SYN **is used. **-ENOSPC **if there is not enough space. Only _len_ number of bytes are copied. **-EFAULT **on failure to parse the header options in the packet. **-EPERM **if the helper cannot be used under the current _skops_**->op**. **long bpf_store_hdr_opt(struct bpf_sock_ops *_**skops_**, const void *_**from_**, u32 _**len_**, u64 _**flags_**)** **Description** Store header option. The data will be copied from buffer _from_ with length _len_ to the TCP header. The buffer _from_ should have the whole option that includes the kind, kind-length, and the actual option data. The _len_ must be at least kind-length long. The kind-length does not have to be 4 byte aligned. The kernel will take care of the padding and setting the 4 bytes aligned value to th->doff. This helper will check for duplicated option by searching the same option in the outgoing skb. This helper can only be called during **BPF_SOCK_OPS_WRITE_HDR_OPT_CB**. **Return **0 on success, or negative error in case of failure: **-EINVAL **If param is invalid. **-ENOSPC **if there is not enough space in the header. Nothing has been written **-EEXIST **if the option already exists. **-EFAULT **on failure to parse the existing header options. **-EPERM **if the helper cannot be used under the current _skops_**->op**. **long bpf_reserve_hdr_opt(struct bpf_sock_ops *_**skops_**, u32 _**len_**, u64 _**flags_**)** **Description** Reserve _len_ bytes for the bpf header option. The space will be used by **bpf_store_hdr_opt**() later in **BPF_SOCK_OPS_WRITE_HDR_OPT_CB**. If **bpf_reserve_hdr_opt**() is called multiple times, the total number of bytes will be reserved. This helper can only be called during **BPF_SOCK_OPS_HDR_OPT_LEN_CB**. **Return **0 on success, or negative error in case of failure: **-EINVAL **if a parameter is invalid. **-ENOSPC **if there is not enough space in the header. **-EPERM **if the helper cannot be used under the current _skops_**->op**. **void *bpf_inode_storage_get(struct bpf_map *_**map_**, void *_**inode_**, void *_**value_**, u64 _**flags_**)** **Description** Get a bpf_local_storage from an _inode_. Logically, it could be thought of as getting the value from a _map_ with _inode_ as the **key**. From this perspective, the usage is not much different from **bpf_map_lookup_elem**(_map_, **&_**inode_) except this helper enforces the key must be an inode and the map must also be a **BPF_MAP_TYPE_INODE_STORAGE**. Underneath, the value is stored locally at _inode_ instead of the _map_. The _map_ is used as the bpf-local-storage "type". The bpf-local-storage "type" (i.e. the _map_) is searched against all bpf_local_storage residing at _inode_. An optional _flags_ (**BPF_LOCAL_STORAGE_GET_F_CREATE**) can be used such that a new bpf_local_storage will be created if one does not exist. _value_ can be used to‐ gether with **BPF_LOCAL_STORAGE_GET_F_CREATE **to specify the initial value of a bpf_local_storage. If _value_ is **NULL**, the new bpf_local_storage will be zero initialized. **Return **A bpf_local_storage pointer is returned on success. **NULL **if not found or there was an error in adding a new bpf_local_storage. **int bpf_inode_storage_delete(struct bpf_map *_**map_**, void *_**inode_**)** **Description** Delete a bpf_local_storage from an _inode_. **Return **0 on success. **-ENOENT **if the bpf_local_storage cannot be found. **long bpf_d_path(struct path *_**path_**, char *_**buf_**, u32 _**sz_**)** **Description** Return full path for given **struct path **object, which needs to be the kernel BTF _path_ object. The path is returned in the provided buffer _buf_ of size _sz_ and is zero terminated. **Return **On success, the strictly positive length of the string, including the trailing NUL character. On error, a negative value. **long bpf_copy_from_user(void *_**dst_**, u32 _**size_**, const void *_**user_ptr_**)** **Description** Read _size_ bytes from user space address _user_ptr_ and store the data in _dst_. This is a wrapper of **copy_from_user**(). **Return **0 on success, or a negative error in case of failure. **long bpf_snprintf_btf(char *_**str_**, u32 _**str_size_**, struct btf_ptr *_**ptr_**, u32 _**btf_ptr_size_**, u64** _flags_**)** **Description** Use BTF to store a string representation of _ptr_->ptr in _str_, using _ptr_->type_id. This value should specify the type that _ptr_->ptr points to. LLVM __builtin_btf_type_id(type, 1) can be used to look up vmlinux BTF type ids. Traversing the data structure using BTF, the type information and values are stored in the first _str_size_ - 1 bytes of _str_. Safe copy of the pointer data is carried out to avoid kernel crashes during operation. Smaller types can use string space on the stack; larger programs can use map data to store the string representation. The string can be subsequently shared with userspace via bpf_perf_event_out‐ put() or ring buffer interfaces. bpf_trace_printk() is to be avoided as it places too small a limit on string size to be useful. _flags_ is a combination of **BTF_F_COMPACT** no formatting around type information **BTF_F_NONAME** no struct/union member names/types **BTF_F_PTR_RAW** show raw (unobfuscated) pointer values; equivalent to printk specifier %px. **BTF_F_ZERO** show zero-valued struct/union members; they are not displayed by default **Return **The number of bytes that were written (or would have been written if output had to be truncated due to string size), or a negative error in cases of failure. **long bpf_seq_printf_btf(struct seq_file *_**m_**, struct btf_ptr *_**ptr_**, u32 _**ptr_size_**, u64 _**flags_**)** **Description** Use BTF to write to seq_write a string representation of _ptr_->ptr, using _ptr_->type_id as per bpf_snprintf_btf(). _flags_ are identical to those used for bpf_snprintf_btf. **Return **0 on success or a negative error in case of failure. **u64 bpf_skb_cgroup_classid(struct sk_buff *_**skb_**)** **Description** See **bpf_get_cgroup_classid**() for the main description. This helper differs from **bpf_get_cgroup_classid**() in that the cgroup v1 net_cls class is retrieved only from the _skb_'s associated socket instead of the current process. **Return **The id is returned or 0 in case the id could not be retrieved. **long bpf_redirect_neigh(u32 _**ifindex_**, struct bpf_redir_neigh *_**params_**, int _**plen_**, u64 _**flags_**)** **Description** Redirect the packet to another net device of index _ifindex_ and fill in L2 ad‐ dresses from neighboring subsystem. This helper is somewhat similar to **bpf_redirect**(), except that it populates L2 addresses as well, meaning, inter‐ nally, the helper relies on the neighbor lookup for the L2 address of the nex‐ thop. The helper will perform a FIB lookup based on the skb's networking header to get the address of the next hop, unless this is supplied by the caller in the _params_ argument. The _plen_ argument indicates the len of _params_ and should be set to 0 if _params_ is NULL. The _flags_ argument is reserved and must be 0. The helper is currently only sup‐ ported for tc BPF program types, and enabled for IPv4 and IPv6 protocols. **Return **The helper returns **TC_ACT_REDIRECT **on success or **TC_ACT_SHOT **on error. **void *bpf_per_cpu_ptr(const void *_**percpu_ptr_**, u32 _**cpu_**)** **Description** Take a pointer to a percpu ksym, _percpu_ptr_, and return a pointer to the percpu kernel variable on _cpu_. A ksym is an extern variable decorated with '__ksym'. For ksym, there is a global var (either static or global) defined of the same name in the kernel. The ksym is percpu if the global var is percpu. The re‐ turned pointer points to the global percpu var on _cpu_. bpf_per_cpu_ptr() has the same semantic as per_cpu_ptr() in the kernel, except that bpf_per_cpu_ptr() may return NULL. This happens if _cpu_ is larger than nr_cpu_ids. The caller of bpf_per_cpu_ptr() must check the returned value. **Return **A pointer pointing to the kernel percpu variable on _cpu_, or NULL, if _cpu_ is in‐ valid. **void *bpf_this_cpu_ptr(const void *_**percpu_ptr_**)** **Description** Take a pointer to a percpu ksym, _percpu_ptr_, and return a pointer to the percpu kernel variable on this cpu. See the description of 'ksym' in **bpf_per_cpu_ptr**(). bpf_this_cpu_ptr() has the same semantic as this_cpu_ptr() in the kernel. Dif‐ ferent from **bpf_per_cpu_ptr**(), it would never return NULL. **Return **A pointer pointing to the kernel percpu variable on this cpu. **long bpf_redirect_peer(u32 _**ifindex_**, u64 _**flags_**)** **Description** Redirect the packet to another net device of index _ifindex_. This helper is somewhat similar to **bpf_redirect**(), except that the redirection happens to the _ifindex_' peer device and the netns switch takes place from ingress to ingress without going through the CPU's backlog queue. The _flags_ argument is reserved and must be 0. The helper is currently only sup‐ ported for tc BPF program types at the ingress hook and for veth device types. The peer device must reside in a different network namespace. **Return **The helper returns **TC_ACT_REDIRECT **on success or **TC_ACT_SHOT **on error. **void *bpf_task_storage_get(struct bpf_map *_**map_**, struct task_struct *_**task_**, void *_**value_**, u64** _flags_**)** **Description** Get a bpf_local_storage from the _task_. Logically, it could be thought of as getting the value from a _map_ with _task_ as the **key**. From this perspective, the usage is not much different from **bpf_map_lookup_elem**(_map_, **&_**task_) except this helper enforces the key must be a task_struct and the map must also be a **BPF_MAP_TYPE_TASK_STORAGE**. Underneath, the value is stored locally at _task_ instead of the _map_. The _map_ is used as the bpf-local-storage "type". The bpf-local-storage "type" (i.e. the _map_) is searched against all bpf_local_storage residing at _task_. An optional _flags_ (**BPF_LOCAL_STORAGE_GET_F_CREATE**) can be used such that a new bpf_local_storage will be created if one does not exist. _value_ can be used to‐ gether with **BPF_LOCAL_STORAGE_GET_F_CREATE **to specify the initial value of a bpf_local_storage. If _value_ is **NULL**, the new bpf_local_storage will be zero initialized. **Return **A bpf_local_storage pointer is returned on success. **NULL **if not found or there was an error in adding a new bpf_local_storage. **long bpf_task_storage_delete(struct bpf_map *_**map_**, struct task_struct *_**task_**)** **Description** Delete a bpf_local_storage from a _task_. **Return **0 on success. **-ENOENT **if the bpf_local_storage cannot be found. **struct task_struct *bpf_get_current_task_btf(void)** **Description** Return a BTF pointer to the "current" task. This pointer can also be used in helpers that accept an _ARG_PTR_TO_BTF_ID_ of type _task_struct_. **Return **Pointer to the current task. **long bpf_bprm_opts_set(struct linux_binprm *_**bprm_**, u64 _**flags_**)** **Description** Set or clear certain options on _bprm_: **BPF_F_BPRM_SECUREEXEC **Set the secureexec bit which sets the **AT_SECURE **auxv for glibc. The bit is cleared if the flag is not specified. **Return -EINVAL **if invalid _flags_ are passed, zero otherwise. ### u64 bpf_ktime_get_coarse_ns(void) **Description** Return a coarse-grained version of the time elapsed since system boot, in nanoseconds. Does not include time the system was suspended. See: **clock_gettime**(**CLOCK_MONOTONIC_COARSE**) **Return **Current _ktime_. **long bpf_ima_inode_hash(struct inode *_**inode_**, void *_**dst_**, u32 _**size_**)** **Description** Returns the stored IMA hash of the _inode_ (if it's available). If the hash is larger than _size_, then only _size_ bytes will be copied to _dst_ **Return **The **hash_algo **is returned on success, **-EOPNOTSUP **if IMA is disabled or **-EINVAL** if invalid arguments are passed. **struct socket *bpf_sock_from_file(struct file *_**file_**)** **Description** If the given file represents a socket, returns the associated socket. **Return **A pointer to a struct socket on success or NULL if the file is not a socket. **long bpf_check_mtu(void *_**ctx_**, u32 _**ifindex_**, u32 *_**mtu_len_**, s32 _**len_diff_**, u64 _**flags_**)** **Description** Check packet size against exceeding MTU of net device (based on _ifindex_). This helper will likely be used in combination with helpers that adjust/change the packet size. The argument _len_diff_ can be used for querying with a planned size change. This allows to check MTU prior to changing packet ctx. Providing a _len_diff_ adjust‐ ment that is larger than the actual packet size (resulting in negative packet size) will in principle not exceed the MTU, which is why it is not considered a failure. Other BPF helpers are needed for performing the planned size change; therefore the responsibility for catching a negative packet size belongs in those helpers. Specifying _ifindex_ zero means the MTU check is performed against the current net device. This is practical if this isn't used prior to redirect. On input _mtu_len_ must be a valid pointer, else verifier will reject BPF pro‐ gram. If the value _mtu_len_ is initialized to zero then the ctx packet size is use. When value _mtu_len_ is provided as input this specify the L3 length that the MTU check is done against. Remember XDP and TC length operate at L2, but this value is L3 as this correlate to MTU and IP-header tot_len values which are L3 (similar behavior as bpf_fib_lookup). The Linux kernel route table can configure MTUs on a more specific per route level, which is not provided by this helper. For route level MTU checks use the **bpf_fib_lookup**() helper. _ctx_ is either **struct xdp_md **for XDP programs or **struct sk_buff **for tc cls_act programs. The _flags_ argument can be a combination of one or more of the following values: **BPF_MTU_CHK_SEGS** This flag will only works for _ctx_ **struct sk_buff**. If packet context contains extra packet segment buffers (often knows as GSO skb), then MTU check is harder to check at this point, because in transmit path it is possible for the skb packet to get re-segmented (depending on net device features). This could still be a MTU violation, so this flag enables performing MTU check against segments, with a different violation return code to tell it apart. Check cannot use len_diff. On return _mtu_len_ pointer contains the MTU value of the net device. Remember the net device configured MTU is the L3 size, which is returned here and XDP and TC length operate at L2. Helper take this into account for you, but remem‐ ber when using MTU value in your BPF-code. **Return** • 0 on success, and populate MTU value in _mtu_len_ pointer. • < 0 if any input argument is invalid (_mtu_len_ not updated) MTU violations return positive values, but also populate MTU value in _mtu_len_ pointer, as this can be needed for implementing PMTU handing: • **BPF_MTU_CHK_RET_FRAG_NEEDED** • **BPF_MTU_CHK_RET_SEGS_TOOBIG** **long bpf_for_each_map_elem(struct bpf_map *_**map_**, void *_**callback_fn_**, void *_**callback_ctx_**, u64** _flags_**)** **Description** For each element in **map**, call **callback_fn **function with **map**, **callback_ctx **and other map-specific parameters. The **callback_fn **should be a static function and the **callback_ctx **should be a pointer to the stack. The **flags **is used to con‐ trol certain aspects of the helper. Currently, the **flags **must be 0. The following are a list of supported map types and their respective expected callback signatures: BPF_MAP_TYPE_HASH, BPF_MAP_TYPE_PERCPU_HASH, BPF_MAP_TYPE_LRU_HASH, BPF_MAP_TYPE_LRU_PERCPU_HASH, BPF_MAP_TYPE_ARRAY, BPF_MAP_TYPE_PERCPU_ARRAY long (*callback_fn)(struct bpf_map *map, const void *key, void *value, void *ctx); For per_cpu maps, the map_value is the value on the cpu where the bpf_prog is running. If **callback_fn **return 0, the helper will continue to the next element. If re‐ turn value is 1, the helper will skip the rest of elements and return. Other return values are not used now. **Return **The number of traversed map elements for success, **-EINVAL **for invalid **flags**. **long bpf_snprintf(char *_**str_**, u32 _**str_size_**, const char *_**fmt_**, u64 *_**data_**, u32 _**data_len_**)** **Description** Outputs a string into the **str **buffer of size **str_size **based on a format string stored in a read-only map pointed by **fmt**. Each format specifier in **fmt **corresponds to one u64 element in the **data **array. For strings and pointers where pointees are accessed, only the pointer values are stored in the _data_ array. The _data_len_ is the size of _data_ in bytes - must be a multiple of 8. Formats **%s **and **%p{i,I}{4,6} **require to read kernel memory. Reading kernel mem‐ ory may fail due to either invalid address or valid address but requiring a ma‐ jor memory fault. If reading kernel memory fails, the string for **%s **will be an empty string, and the ip address for **%p{i,I}{4,6} **will be 0. Not returning er‐ ror to bpf program is consistent with what **bpf_trace_printk**() does for now. **Return **The strictly positive length of the formatted string, including the trailing zero character. If the return value is greater than **str_size**, **str **contains a truncated string, guaranteed to be zero-terminated except when **str_size **is 0. Or **-EBUSY **if the per-CPU memory copy buffer is busy. **long bpf_sys_bpf(u32 _**cmd_**, void *_**attr_**, u32 _**attr_size_**)** **Description** Execute bpf syscall with given arguments. **Return **A syscall result. **long bpf_btf_find_by_name_kind(char *_**name_**, int _**name_sz_**, u32 _**kind_**, int _**flags_**)** **Description** Find BTF type with given name and kind in vmlinux BTF or in module's BTFs. **Return **Returns btf_id and btf_obj_fd in lower and upper 32 bits. **long bpf_sys_close(u32 _**fd_**)** **Description** Execute close syscall for given FD. **Return **A syscall result. **long bpf_timer_init(struct bpf_timer *_**timer_**, struct bpf_map *_**map_**, u64 _**flags_**)** **Description** Initialize the timer. First 4 bits of _flags_ specify clockid. Only CLOCK_MO‐ NOTONIC, CLOCK_REALTIME, CLOCK_BOOTTIME are allowed. All other bits of _flags_ are reserved. The verifier will reject the program if _timer_ is not from the same _map_. **Return **0 on success. **-EBUSY **if _timer_ is already initialized. **-EINVAL **if invalid _flags_ are passed. **-EPERM **if _timer_ is in a map that doesn't have any user ref‐ erences. The user space should either hold a file descriptor to a map with timers or pin such map in bpffs. When map is unpinned or file descriptor is closed all timers in the map will be cancelled and freed. **long bpf_timer_set_callback(struct bpf_timer *_**timer_**, void *_**callback_fn_**)** **Description** Configure the timer to call _callback_fn_ static function. **Return **0 on success. **-EINVAL **if _timer_ was not initialized with bpf_timer_init() ear‐ lier. **-EPERM **if _timer_ is in a map that doesn't have any user references. The user space should either hold a file descriptor to a map with timers or pin such map in bpffs. When map is unpinned or file descriptor is closed all timers in the map will be cancelled and freed. **long bpf_timer_start(struct bpf_timer *_**timer_**, u64 _**nsecs_**, u64 _**flags_**)** **Description** Set timer expiration N nanoseconds from the current time. The configured call‐ back will be invoked in soft irq context on some cpu and will not repeat unless another bpf_timer_start() is made. In such case the next invocation can mi‐ grate to a different cpu. Since struct bpf_timer is a field inside map element the map owns the timer. The bpf_timer_set_callback() will increment refcnt of BPF program to make sure that callback_fn code stays valid. When user space reference to a map reaches zero all timers in a map are cancelled and corre‐ sponding program's refcnts are decremented. This is done to make sure that Ctrl-C of a user process doesn't leave any timers running. If map is pinned in bpffs the callback_fn can re-arm itself indefinitely. bpf_map_up‐ date/delete_elem() helpers and user space sys_bpf commands cancel and free the timer in the given map element. The map can contain timers that invoke call‐ back_fn-s from different programs. The same callback_fn can serve different timers from different maps if key/value layout matches across maps. Every bpf_timer_set_callback() can have different callback_fn. _flags_ can be one of: **BPF_F_TIMER_ABS** Start the timer in absolute expire value instead of the default relative one. **BPF_F_TIMER_CPU_PIN** Timer will be pinned to the CPU of the caller. **Return **0 on success. **-EINVAL **if _timer_ was not initialized with bpf_timer_init() ear‐ lier or invalid _flags_ are passed. **long bpf_timer_cancel(struct bpf_timer *_**timer_**)** **Description** Cancel the timer and wait for callback_fn to finish if it was running. **Return **0 if the timer was not active. 1 if the timer was active. **-EINVAL **if _timer_ was not initialized with bpf_timer_init() earlier. **-EDEADLK **if callback_fn tried to call bpf_timer_cancel() on its own timer which would have led to a deadlock otherwise. **u64 bpf_get_func_ip(void *_**ctx_**)** **Description** Get address of the traced function (for tracing and kprobe programs). When called for kprobe program attached as uprobe it returns probe address for both entry and return uprobe. **Return **Address of the traced function for kprobe. 0 for kprobes placed within the function (not at the entry). Address of the probe for uprobe and return up‐ robe. **u64 bpf_get_attach_cookie(void *_**ctx_**)** **Description** Get bpf_cookie value provided (optionally) during the program attachment. It might be different for each individual attachment, even if BPF program itself is the same. Expects BPF program context _ctx_ as a first argument. **Supported for the following program types:** • kprobe/uprobe; • tracepoint; • perf_event. **Return **Value specified by user at BPF link creation/attachment time or 0, if it was not specified. **long bpf_task_pt_regs(struct task_struct *_**task_**)** **Description** Get the struct pt_regs associated with **task**. **Return **A pointer to struct pt_regs. **long bpf_get_branch_snapshot(void *_**entries_**, u32 _**size_**, u64 _**flags_**)** **Description** Get branch trace from hardware engines like Intel LBR. The hardware engine is stopped shortly after the helper is called. Therefore, the user need to filter branch entries based on the actual use case. To capture branch trace before the trigger point of the BPF program, the helper should be called at the beginning of the BPF program. The data is stored as struct perf_branch_entry into output buffer _entries_. _size_ is the size of _entries_ in bytes. _flags_ is reserved for now and must be zero. **Return **On success, number of bytes written to _buf_. On error, a negative value. **-EINVAL **if _flags_ is not zero. **-ENOENT **if architecture does not support branch records. **long bpf_trace_vprintk(const char *_**fmt_**, u32 _**fmt_size_**, const void *_**data_**, u32 _**data_len_**)** **Description** Behaves like **bpf_trace_printk**() helper, but takes an array of u64 to format and can handle more format args as a result. Arguments are to be used as in **bpf_seq_printf**() helper. **Return **The number of bytes written to the buffer, or a negative error in case of fail‐ ure. **struct unix_sock *bpf_skc_to_unix_sock(void *_**sk_**)** **Description** Dynamically cast a _sk_ pointer to a _unix_sock_ pointer. **Return _**sk_ if casting is valid, or **NULL **otherwise. **long bpf_kallsyms_lookup_name(const char *_**name_**, int _**name_sz_**, int _**flags_**, u64 *_**res_**)** **Description** Get the address of a kernel symbol, returned in _res_. _res_ is set to 0 if the symbol is not found. **Return **On success, zero. On error, a negative value. **-EINVAL **if _flags_ is not zero. **-EINVAL **if string _name_ is not the same size as _name_sz_. **-ENOENT **if symbol is not found. **-EPERM **if caller does not have permission to obtain kernel address. **long bpf_find_vma(struct task_struct *_**task_**, u64 _**addr_**, void *_**callback_fn_**, void *_**callback_ctx_**,** **u64 _**flags_**)** **Description** Find vma of _task_ that contains _addr_, call _callback_fn_ function with _task_, _vma_, and _callback_ctx_. The _callback_fn_ should be a static function and the _call‐_ _back_ctx_ should be a pointer to the stack. The _flags_ is used to control cer‐ tain aspects of the helper. Currently, the _flags_ must be 0. The expected callback signature is long (*callback_fn)(struct task_struct *task, struct vm_area_struct *vma, void *callback_ctx); **Return **0 on success. **-ENOENT **if _task->mm_ is NULL, or no vma contains _addr_. **-EBUSY **if failed to try lock mmap_lock. **-EINVAL **for invalid **flags**. **long bpf_loop(u32 _**nr_loops_**, void *_**callback_fn_**, void *_**callback_ctx_**, u64 _**flags_**)** **Description** For **nr_loops**, call **callback_fn **function with **callback_ctx **as the context para‐ meter. The **callback_fn **should be a static function and the **callback_ctx **should be a pointer to the stack. The **flags **is used to control certain aspects of the helper. Currently, the **flags **must be 0. Currently, nr_loops is limited to 1 << 23 (~8 million) loops. long (*callback_fn)(u32 index, void *ctx); where **index **is the current index in the loop. The index is zero-indexed. If **callback_fn **returns 0, the helper will continue to the next loop. If return value is 1, the helper will skip the rest of the loops and return. Other return values are not used now, and will be rejected by the verifier. **Return **The number of loops performed, **-EINVAL **for invalid **flags**, **-E2BIG **if **nr_loops** exceeds the maximum number of loops. **long bpf_strncmp(const char *_**s1_**, u32 _**s1_sz_**, const char *_**s2_**)** **Description** Do strncmp() between **s1 **and **s2**. **s1 **doesn't need to be null-terminated and **s1_sz** is the maximum storage size of **s1**. **s2 **must be a read-only string. **Return **An integer less than, equal to, or greater than zero if the first **s1_sz **bytes of **s1 **is found to be less than, to match, or be greater than **s2**. **long bpf_get_func_arg(void *_**ctx_**, u32 _**n_**, u64 *_**value_**)** **Description** Get **n**-th argument register (zero based) of the traced function (for tracing programs) returned in **value**. **Return **0 on success. **-EINVAL **if n >= argument register count of traced function. **long bpf_get_func_ret(void *_**ctx_**, u64 *_**value_**)** **Description** Get return value of the traced function (for tracing programs) in **value**. **Return **0 on success. **-EOPNOTSUPP **for tracing programs other than BPF_TRACE_FEXIT or BPF_MODIFY_RETURN. **long bpf_get_func_arg_cnt(void *_**ctx_**)** **Description** Get number of registers of the traced function (for tracing programs) where function arguments are stored in these registers. **Return **The number of argument registers of the traced function. ### int bpf_get_retval(void) **Description** Get the BPF program's return value that will be returned to the upper layers. This helper is currently supported by cgroup programs and only by the hooks where BPF program's return value is returned to the userspace via errno. **Return **The BPF program's return value. **int bpf_set_retval(int _**retval_**)** **Description** Set the BPF program's return value that will be returned to the upper layers. This helper is currently supported by cgroup programs and only by the hooks where BPF program's return value is returned to the userspace via errno. Note that there is the following corner case where the program exports an error via bpf_set_retval but signals success via 'return 1': bpf_set_retval(-EPERM); return 1; In this case, the BPF program's return value will use helper's -EPERM. This still holds true for cgroup/bind{4,6} which supports extra 'return 3' success case. **Return **0 on success, or a negative error in case of failure. **u64 bpf_xdp_get_buff_len(struct xdp_buff *_**xdp_md_**)** **Description** Get the total size of a given xdp buff (linear and paged area) **Return **The total size of a given xdp buffer. **long bpf_xdp_load_bytes(struct xdp_buff *_**xdp_md_**, u32 _**offset_**, void *_**buf_**, u32 _**len_**)** **Description** This helper is provided as an easy way to load data from a xdp buffer. It can be used to load _len_ bytes from _offset_ from the frame associated to _xdp_md_, into the buffer pointed by _buf_. **Return **0 on success, or a negative error in case of failure. **long bpf_xdp_store_bytes(struct xdp_buff *_**xdp_md_**, u32 _**offset_**, void *_**buf_**, u32 _**len_**)** **Description** Store _len_ bytes from buffer _buf_ into the frame associated to _xdp_md_, at _offset_. **Return **0 on success, or a negative error in case of failure. **long bpf_copy_from_user_task(void *_**dst_**, u32 _**size_**, const void *_**user_ptr_**, struct task_struct** ***_**tsk_**, u64 _**flags_**)** **Description** Read _size_ bytes from user space address _user_ptr_ in _tsk_'s address space, and stores the data in _dst_. _flags_ is not used yet and is provided for future exten‐ sibility. This helper can only be used by sleepable programs. **Return **0 on success, or a negative error in case of failure. On error _dst_ buffer is zeroed out. **long bpf_skb_set_tstamp(struct sk_buff *_**skb_**, u64 _**tstamp_**, u32 _**tstamp_type_**)** **Description** Change the __sk_buff->tstamp_type to _tstamp_type_ and set _tstamp_ to the __sk_buff->tstamp together. If there is no need to change the __sk_buff->tstamp_type, the tstamp value can be directly written to __sk_buff->tstamp instead. BPF_SKB_TSTAMP_DELIVERY_MONO is the only tstamp that will be kept during bpf_redirect_*(). A non zero _tstamp_ must be used with the BPF_SKB_TSTAMP_DE‐ LIVERY_MONO _tstamp_type_. A BPF_SKB_TSTAMP_UNSPEC _tstamp_type_ can only be used with a zero _tstamp_. Only IPv4 and IPv6 skb->protocol are supported. This function is most useful when it needs to set a mono delivery time to __sk_buff->tstamp and then bpf_redirect_*() to the egress of an iface. For ex‐ ample, changing the (rcv) timestamp in __sk_buff->tstamp at ingress to a mono delivery time and then bpf_redirect_*() to _sch_fq@phy-dev_. **Return **0 on success. **-EINVAL **for invalid input **-EOPNOTSUPP **for unsupported protocol **long bpf_ima_file_hash(struct file *_**file_**, void *_**dst_**, u32 _**size_**)** **Description** Returns a calculated IMA hash of the _file_. If the hash is larger than _size_, then only _size_ bytes will be copied to _dst_ **Return **The **hash_algo **is returned on success, **-EOPNOTSUP **if the hash calculation failed or **-EINVAL **if invalid arguments are passed. **void *bpf_kptr_xchg(void *_**map_value_**, void *_**ptr_**)** **Description** Exchange kptr at pointer _map_value_ with _ptr_, and return the old value. _ptr_ can be NULL, otherwise it must be a referenced pointer which will be released when this helper is called. **Return **The old value of kptr (which can be NULL). The returned pointer if not NULL, is a reference which must be released using its corresponding release function, or moved into a BPF map before program exit. **void *bpf_map_lookup_percpu_elem(struct bpf_map *_**map_**, const void *_**key_**, u32 _**cpu_**)** **Description** Perform a lookup in _percpu_ _map_ for an entry associated to _key_ on _cpu_. **Return **Map value associated to _key_ on _cpu_, or **NULL **if no entry was found or _cpu_ is in‐ valid. **struct mptcp_sock *bpf_skc_to_mptcp_sock(void *_**sk_**)** **Description** Dynamically cast a _sk_ pointer to a _mptcp_sock_ pointer. **Return _**sk_ if casting is valid, or **NULL **otherwise. **long bpf_dynptr_from_mem(void *_**data_**, u32 _**size_**, u64 _**flags_**, struct bpf_dynptr *_**ptr_**)** **Description** Get a dynptr to local memory _data_. _data_ must be a ptr to a map value. The maximum _size_ supported is DYNPTR_MAX_SIZE. _flags_ is currently unused. **Return **0 on success, -E2BIG if the size exceeds DYNPTR_MAX_SIZE, -EINVAL if flags is not 0. **long bpf_ringbuf_reserve_dynptr(void *_**ringbuf_**, u32 _**size_**, u64 _**flags_**, struct bpf_dynptr *_**ptr_**)** **Description** Reserve _size_ bytes of payload in a ring buffer _ringbuf_ through the dynptr in‐ terface. _flags_ must be 0. Please note that a corresponding bpf_ringbuf_submit_dynptr or bpf_ringbuf_dis‐ card_dynptr must be called on _ptr_, even if the reservation fails. This is en‐ forced by the verifier. **Return **0 on success, or a negative error in case of failure. **void bpf_ringbuf_submit_dynptr(struct bpf_dynptr *_**ptr_**, u64 _**flags_**)** **Description** Submit reserved ring buffer sample, pointed to by _data_, through the dynptr in‐ terface. This is a no-op if the dynptr is invalid/null. For more information on _flags_, please see 'bpf_ringbuf_submit'. **Return **Nothing. Always succeeds. **void bpf_ringbuf_discard_dynptr(struct bpf_dynptr *_**ptr_**, u64 _**flags_**)** **Description** Discard reserved ring buffer sample through the dynptr interface. This is a no-op if the dynptr is invalid/null. For more information on _flags_, please see 'bpf_ringbuf_discard'. **Return **Nothing. Always succeeds. **long bpf_dynptr_read(void *_**dst_**, u32 _**len_**, const struct bpf_dynptr *_**src_**, u32 _**offset_**, u64 _**flags_**)** **Description** Read _len_ bytes from _src_ into _dst_, starting from _offset_ into _src_. _flags_ is cur‐ rently unused. **Return **0 on success, -E2BIG if _offset_ + _len_ exceeds the length of _src_'s data, -EINVAL if _src_ is an invalid dynptr or if _flags_ is not 0. **long bpf_dynptr_write(const struct bpf_dynptr *_**dst_**, u32 _**offset_**, void *_**src_**, u32 _**len_**, u64** _flags_**)** **Description** Write _len_ bytes from _src_ into _dst_, starting from _offset_ into _dst_. _flags_ must be 0 except for skb-type dynptrs. **For skb-type dynptrs:** • All data slices of the dynptr are automatically invalidated after **bpf_dynptr_write**(). This is because writing may pull the skb and change the underlying packet buffer. • For _flags_, please see the flags accepted by **bpf_skb_store_bytes**(). **Return **0 on success, -E2BIG if _offset_ + _len_ exceeds the length of _dst_'s data, -EINVAL if _dst_ is an invalid dynptr or if _dst_ is a read-only dynptr or if _flags_ is not correct. For skb-type dynptrs, other errors correspond to errors returned by **bpf_skb_store_bytes**(). **void *bpf_dynptr_data(const struct bpf_dynptr *_**ptr_**, u32 _**offset_**, u32 _**len_**)** **Description** Get a pointer to the underlying dynptr data. _len_ must be a statically known value. The returned data slice is invalidated whenever the dynptr is invalidated. skb and xdp type dynptrs may not use bpf_dynptr_data. They should instead use bpf_dynptr_slice and bpf_dynptr_slice_rdwr. **Return **Pointer to the underlying dynptr data, NULL if the dynptr is read-only, if the dynptr is invalid, or if the offset and length is out of bounds. **s64 bpf_tcp_raw_gen_syncookie_ipv4(struct iphdr *_**iph_**, struct tcphdr *_**th_**, u32 _**th_len_**)** **Description** Try to issue a SYN cookie for the packet with corresponding IPv4/TCP headers, _iph_ and _th_, without depending on a listening socket. _iph_ points to the IPv4 header. _th_ points to the start of the TCP header, while _th_len_ contains the length of the TCP header (at least **sizeof**(**struct tcphdr**)). **Return **On success, lower 32 bits hold the generated SYN cookie in followed by 16 bits which hold the MSS value for that cookie, and the top 16 bits are unused. On failure, the returned value is one of the following: **-EINVAL **if _th_len_ is invalid. **s64 bpf_tcp_raw_gen_syncookie_ipv6(struct ipv6hdr *_**iph_**, struct tcphdr *_**th_**, u32 _**th_len_**)** **Description** Try to issue a SYN cookie for the packet with corresponding IPv6/TCP headers, _iph_ and _th_, without depending on a listening socket. _iph_ points to the IPv6 header. _th_ points to the start of the TCP header, while _th_len_ contains the length of the TCP header (at least **sizeof**(**struct tcphdr**)). **Return **On success, lower 32 bits hold the generated SYN cookie in followed by 16 bits which hold the MSS value for that cookie, and the top 16 bits are unused. On failure, the returned value is one of the following: **-EINVAL **if _th_len_ is invalid. **-EPROTONOSUPPORT **if CONFIG_IPV6 is not builtin. **long bpf_tcp_raw_check_syncookie_ipv4(struct iphdr *_**iph_**, struct tcphdr *_**th_**)** **Description** Check whether _iph_ and _th_ contain a valid SYN cookie ACK without depending on a listening socket. _iph_ points to the IPv4 header. _th_ points to the TCP header. **Return **0 if _iph_ and _th_ are a valid SYN cookie ACK. On failure, the returned value is one of the following: **-EACCES **if the SYN cookie is not valid. **long bpf_tcp_raw_check_syncookie_ipv6(struct ipv6hdr *_**iph_**, struct tcphdr *_**th_**)** **Description** Check whether _iph_ and _th_ contain a valid SYN cookie ACK without depending on a listening socket. _iph_ points to the IPv6 header. _th_ points to the TCP header. **Return **0 if _iph_ and _th_ are a valid SYN cookie ACK. On failure, the returned value is one of the following: **-EACCES **if the SYN cookie is not valid. **-EPROTONOSUPPORT **if CONFIG_IPV6 is not builtin. ### u64 bpf_ktime_get_tai_ns(void) **Description** A nonsettable system-wide clock derived from wall-clock time but ignoring leap seconds. This clock does not experience discontinuities and backwards jumps caused by NTP inserting leap seconds as CLOCK_REALTIME does. See: **clock_gettime**(**CLOCK_TAI**) **Return **Current _ktime_. **long bpf_user_ringbuf_drain(struct bpf_map *_**map_**, void *_**callback_fn_**, void *_**ctx_**, u64 _**flags_**)** **Description** Drain samples from the specified user ring buffer, and invoke the provided callback for each such sample: long (*callback_fn)(const struct bpf_dynptr *dynptr, void *ctx); If **callback_fn **returns 0, the helper will continue to try and drain the next sample, up to a maximum of BPF_MAX_USER_RINGBUF_SAMPLES samples. If the return value is 1, the helper will skip the rest of the samples and return. Other re‐ turn values are not used now, and will be rejected by the verifier. **Return **The number of drained samples if no error was encountered while draining sam‐ ples, or 0 if no samples were present in the ring buffer. If a user-space pro‐ ducer was epoll-waiting on this map, and at least one sample was drained, they will receive an event notification notifying them of available space in the ring buffer. If the BPF_RB_NO_WAKEUP flag is passed to this function, no wakeup notification will be sent. If the BPF_RB_FORCE_WAKEUP flag is passed, a wakeup notification will be sent even if no sample was drained. On failure, the returned value is one of the following: **-EBUSY **if the ring buffer is contended, and another calling context was concur‐ rently draining the ring buffer. **-EINVAL **if user-space is not properly tracking the ring buffer due to the pro‐ ducer position not being aligned to 8 bytes, a sample not being aligned to 8 bytes, or the producer position not matching the advertised length of a sample. **-E2BIG **if user-space has tried to publish a sample which is larger than the size of the ring buffer, or which cannot fit within a struct bpf_dynptr. **void *bpf_cgrp_storage_get(struct bpf_map *_**map_**, struct cgroup *_**cgroup_**, void *_**value_**, u64** _flags_**)** **Description** Get a bpf_local_storage from the _cgroup_. Logically, it could be thought of as getting the value from a _map_ with _cgroup_ as the **key**. From this perspective, the usage is not much different from **bpf_map_lookup_elem**(_map_, **&_**cgroup_) except this helper enforces the key must be a cgroup struct and the map must also be a **BPF_MAP_TYPE_CGRP_STORAGE**. In reality, the local-storage value is embedded directly inside of the _cgroup_ object itself, rather than being located in the **BPF_MAP_TYPE_CGRP_STORAGE **map. When the local-storage value is queried for some _map_ on a _cgroup_ object, the kernel will perform an [O(n)](https://www.chedong.com/phpMan.php/man/O/n/markdown) iteration over all of the live local-storage values for that _cgroup_ object until the local-storage value for the _map_ is found. An optional _flags_ (**BPF_LOCAL_STORAGE_GET_F_CREATE**) can be used such that a new bpf_local_storage will be created if one does not exist. _value_ can be used to‐ gether with **BPF_LOCAL_STORAGE_GET_F_CREATE **to specify the initial value of a bpf_local_storage. If _value_ is **NULL**, the new bpf_local_storage will be zero initialized. **Return **A bpf_local_storage pointer is returned on success. **NULL **if not found or there was an error in adding a new bpf_local_storage. **long bpf_cgrp_storage_delete(struct bpf_map *_**map_**, struct cgroup *_**cgroup_**)** **Description** Delete a bpf_local_storage from a _cgroup_. **Return **0 on success. **-ENOENT **if the bpf_local_storage cannot be found. ## EXAMPLES Example usage for most of the eBPF helpers listed in this manual page are available within the Linux kernel sources, at the following locations: • _samples/bpf/_ • _tools/testing/selftests/bpf/_ ## LICENSE eBPF programs can have an associated license, passed along with the bytecode instructions to the kernel when the programs are loaded. The format for that string is identical to the one in use for kernel modules (Dual licenses, such as "Dual BSD/GPL", may be used). Some helper functions are only accessible to programs that are compatible with the GNU General Public Li‐ cense (GNU GPL). In order to use such helpers, the eBPF program must be loaded with the correct license string passed (via **attr**) to the **bpf**() system call, and this generally translates into the C source code of the program containing a line similar to the following: char ____license[] __attribute__((section("license"), used)) = "GPL"; ## IMPLEMENTATION This manual page is an effort to document the existing eBPF helper functions. But as of this writing, the BPF sub-system is under heavy development. New eBPF program or map types are added, along with new helper functions. Some helpers are occasionally made available for ad‐ ditional program types. So in spite of the efforts of the community, this page might not be up-to-date. If you want to check by yourself what helper functions exist in your kernel, or what types of programs they can support, here are some files among the kernel tree that you may be interested in: • _include/uapi/linux/bpf.h_ is the main BPF header. It contains the full list of all helper functions, as well as many other BPF definitions including most of the flags, structs or constants used by the helpers. • _net/core/filter.c_ contains the definition of most network-related helper functions, and the list of program types from which they can be used. • _kernel/trace/bpf_trace.c_ is the equivalent for most tracing program-related helpers. • _kernel/bpf/verifier.c_ contains the functions used to check that valid types of eBPF maps are used with a given helper function. • _kernel/bpf/_ directory contains other files in which additional helpers are defined (for cgroups, sockmaps, etc.). • The bpftool utility can be used to probe the availability of helper functions on the system (as well as supported program and map types, and a number of other parameters). To do so, run **bpftool feature probe **(see [**bpftool-feature**(8)](https://www.chedong.com/phpMan.php/man/bpftool-feature/8/markdown) for details). Add the **unprivileged **key‐ word to list features available to unprivileged users. Compatibility between helper functions and program types can generally be found in the files where helper functions are defined. Look for the **struct bpf_func_proto **objects and for func‐ tions returning them: these functions contain a list of helpers that a given program type can call. Note that the **default: **label of the **switch ... case **used to filter helpers can call other functions, themselves allowing access to additional helpers. The requirement for GPL license is also in those **struct bpf_func_proto**. Compatibility between helper functions and map types can be found in the **check_map_func_com‐** **patibility**() function in file _kernel/bpf/verifier.c_. Helper functions that invalidate the checks on **data **and **data_end **pointers for network pro‐ cessing are listed in function **bpf_helper_changes_pkt_data**() in file _net/core/filter.c_. ## SEE ALSO [**bpf**(2)](https://www.chedong.com/phpMan.php/man/bpf/2/markdown), [**bpftool**(8)](https://www.chedong.com/phpMan.php/man/bpftool/8/markdown), [**cgroups**(7)](https://www.chedong.com/phpMan.php/man/cgroups/7/markdown), [**ip**(8)](https://www.chedong.com/phpMan.php/man/ip/8/markdown), [**perf_event_open**(2)](https://www.chedong.com/phpMan.php/man/perfeventopen/2/markdown), [**sendmsg**(2)](https://www.chedong.com/phpMan.php/man/sendmsg/2/markdown), [**socket**(7)](https://www.chedong.com/phpMan.php/man/socket/7/markdown), [**tc-bpf**(8)](https://www.chedong.com/phpMan.php/man/tc-bpf/8/markdown) Linux v6.8 2023-11-10 [_BPF-HELPERS_(7)](https://www.chedong.com/phpMan.php/man/BPF-HELPERS/7/markdown)