# phpman > man > spufs(7) [SPUFS(7)](https://www.chedong.com/phpMan.php/man/SPUFS/7/markdown) Linux Programmer's Manual [SPUFS(7)](https://www.chedong.com/phpMan.php/man/SPUFS/7/markdown) ## NAME spufs - SPU filesystem ## DESCRIPTION The SPU filesystem is used on PowerPC machines that implement the Cell Broadband Engine Ar‐ chitecture in order to access Synergistic Processor Units (SPUs). The filesystem provides a name space similar to POSIX shared memory or message queues. Users that have write permissions on the filesystem can use **spu**___**[create**(2)](https://www.chedong.com/phpMan.php/man/create/2/markdown) to establish SPU contexts under the **spufs** root directory. Every SPU context is represented by a directory containing a predefined set of files. These files can be used for manipulating the state of the logical SPU. Users can change permis‐ sions on the files, but can't add or remove files. ### Mount options ### uid= Set the user owning the mount point; the default is 0 (root). ### gid= Set the group owning the mount point; the default is 0 (root). ### mode= Set the mode of the top-level directory in **spufs**, as an octal mode string. The de‐ fault is 0775. ### Files The files in **spufs** mostly follow the standard behavior for regular system calls like [**read**(2)](https://www.chedong.com/phpMan.php/man/read/2/markdown) or [**write**(2)](https://www.chedong.com/phpMan.php/man/write/2/markdown), but often support only a subset of the operations supported on regular filesys‐ tems. This list details the supported operations and the deviations from the standard behav‐ ior described in the respective man pages. All files that support the [**read**(2)](https://www.chedong.com/phpMan.php/man/read/2/markdown) operation also support [**readv**(2)](https://www.chedong.com/phpMan.php/man/readv/2/markdown) and all files that support the [**write**(2)](https://www.chedong.com/phpMan.php/man/write/2/markdown) operation also support [**writev**(2)](https://www.chedong.com/phpMan.php/man/writev/2/markdown). All files support the [**access**(2)](https://www.chedong.com/phpMan.php/man/access/2/markdown) and [**stat**(2)](https://www.chedong.com/phpMan.php/man/stat/2/markdown) family of operations, but for the latter call, the only fields of the returned _stat_ structure that contain reliable information are _st_mode_, _st_nlink_, _st_uid_, and _st_gid_. All files support the [**chmod**(2)](https://www.chedong.com/phpMan.php/man/chmod/2/markdown)/[**fchmod**(2)](https://www.chedong.com/phpMan.php/man/fchmod/2/markdown) and [**chown**(2)](https://www.chedong.com/phpMan.php/man/chown/2/markdown)/[**fchown**(2)](https://www.chedong.com/phpMan.php/man/fchown/2/markdown) operations, but will not be able to grant permissions that contradict the possible operations (e.g., read access on the _wbox_ file). The current set of files is: _/capabilities_ Contains a comma-delimited string representing the capabilities of this SPU context. Possible capabilities are: **sched** This context may be scheduled. **step** This context can be run in single-step mode, for debugging. New capabilities flags may be added in the future. _/mem_ the contents of the local storage memory of the SPU. This can be accessed like a reg‐ ular shared memory file and contains both code and data in the address space of the SPU. The possible operations on an open _mem_ file are: [**read**(2)](https://www.chedong.com/phpMan.php/man/read/2/markdown), [**pread**(2)](https://www.chedong.com/phpMan.php/man/pread/2/markdown), [**write**(2)](https://www.chedong.com/phpMan.php/man/write/2/markdown), [**pwrite**(2)](https://www.chedong.com/phpMan.php/man/pwrite/2/markdown), [**lseek**(2)](https://www.chedong.com/phpMan.php/man/lseek/2/markdown) These operate as usual, with the exception that [**lseek**(2)](https://www.chedong.com/phpMan.php/man/lseek/2/markdown), [**write**(2)](https://www.chedong.com/phpMan.php/man/write/2/markdown), and [**pwrite**(2)](https://www.chedong.com/phpMan.php/man/pwrite/2/markdown) are not supported beyond the end of the file. The file size is the size of the local storage of the SPU, which is normally 256 kilobytes. [**mmap**(2)](https://www.chedong.com/phpMan.php/man/mmap/2/markdown) Mapping _mem_ into the process address space provides access to the SPU local storage within the process address space. Only **MAP**___**SHARED** mappings are al‐ lowed. _/regs_ Contains the saved general-purpose registers of the SPU context. This file contains the 128-bit values of each register, from register 0 to register 127, in order. This allows the general-purpose registers to be inspected for debugging. Reading to or writing from this file requires that the context is scheduled out, so use of this file is not recommended in normal program operation. The _regs_ file is not present on contexts that have been created with the **SPU**___**CRE**‐‐ **ATE**___**NOSCHED** flag. _/mbox_ The first SPU-to-CPU communication mailbox. This file is read-only and can be read in units of 4 bytes. The file can be used only in nonblocking mode - even [**poll**(2)](https://www.chedong.com/phpMan.php/man/poll/2/markdown) cannot be used to block on this file. The only possible operation on an open _mbox_ file is: [**read**(2)](https://www.chedong.com/phpMan.php/man/read/2/markdown) If _count_ is smaller than four, [**read**(2)](https://www.chedong.com/phpMan.php/man/read/2/markdown) returns -1 and sets _errno_ to **EINVAL**. If there is no data available in the mailbox (i.e., the SPU has not sent a mailbox message), the return value is set to -1 and _errno_ is set to **EAGAIN**. When data has been read successfully, four bytes are placed in the data buffer and the value four is returned. _/ibox_ The second SPU-to-CPU communication mailbox. This file is similar to the first mail‐ box file, but can be read in blocking I/O mode, thus calling [**read**(2)](https://www.chedong.com/phpMan.php/man/read/2/markdown) on an open _ibox_ file will block until the SPU has written data to its interrupt mailbox channel (un‐ less the file has been opened with **O**___**NONBLOCK**, see below). Also, [**poll**(2)](https://www.chedong.com/phpMan.php/man/poll/2/markdown) and similar system calls can be used to monitor for the presence of mailbox data. The possible operations on an open _ibox_ file are: [**read**(2)](https://www.chedong.com/phpMan.php/man/read/2/markdown) If _count_ is smaller than four, [**read**(2)](https://www.chedong.com/phpMan.php/man/read/2/markdown) returns -1 and sets _errno_ to **EINVAL**. If there is no data available in the mailbox and the file descriptor has been opened with **O**___**NONBLOCK**, the return value is set to -1 and _errno_ is set to **EA**‐‐ **GAIN**. If there is no data available in the mailbox and the file descriptor has been opened without **O**___**NONBLOCK**, the call will block until the SPU writes to its in‐ terrupt mailbox channel. When data has been read successfully, four bytes are placed in the data buffer and the value four is returned. [**poll**(2)](https://www.chedong.com/phpMan.php/man/poll/2/markdown) Poll on the _ibox_ file returns _(POLLIN_ _|_ _POLLRDNORM)_ whenever data is available for reading. _/wbox_ The CPU-to-SPU communication mailbox. It is write-only and can be written in units of four bytes. If the mailbox is full, [**write**(2)](https://www.chedong.com/phpMan.php/man/write/2/markdown) will block, and [**poll**(2)](https://www.chedong.com/phpMan.php/man/poll/2/markdown) can be used to block until the mailbox is available for writing again. The possible operations on an open _wbox_ file are: [**write**(2)](https://www.chedong.com/phpMan.php/man/write/2/markdown) If _count_ is smaller than four, [**write**(2)](https://www.chedong.com/phpMan.php/man/write/2/markdown) returns -1 and sets _errno_ to **EINVAL**. If there is no space available in the mailbox and the file descriptor has been opened with **O**___**NONBLOCK**, the return value is set to -1 and _errno_ is set to **EA**‐‐ **GAIN**. If there is no space available in the mailbox and the file descriptor has been opened without **O**___**NONBLOCK**, the call will block until the SPU reads from its PPE (PowerPC Processing Element) mailbox channel. When data has been written suc‐ cessfully, the system call returns four as its function result. [**poll**(2)](https://www.chedong.com/phpMan.php/man/poll/2/markdown) A poll on the _wbox_ file returns _(POLLOUT_ _|_ _POLLWRNORM)_ whenever space is avail‐ able for writing. _/mbox_stat_, _/ibox_stat_, _/wbox_stat_ These are read-only files that contain the length of the current queue of each mail‐ box—that is, how many words can be read from _mbox_ or _ibox_ or how many words can be written to _wbox_ without blocking. The files can be read only in four-byte units and return a big-endian binary integer number. The only possible operation on an open _*box_stat_ file is: [**read**(2)](https://www.chedong.com/phpMan.php/man/read/2/markdown) If _count_ is smaller than four, [**read**(2)](https://www.chedong.com/phpMan.php/man/read/2/markdown) returns -1 and sets _errno_ to **EINVAL**. Otherwise, a four-byte value is placed in the data buffer. This value is the number of elements that can be read from (for _mbox_stat_ and _ibox_stat_) or writ‐ ten to (for _wbox_stat_) the respective mailbox without blocking or returning an **EAGAIN** error. _/npc_, _/decr_, _/decr_status_, _/spu_tag_mask_, _/event_mask_, _/event_status_, _/srr0_, _/lslr_ Internal registers of the SPU. These files contain an ASCII string representing the hex value of the specified register. Reads and writes on these files (except for _npc_, see below) require that the SPU context be scheduled out, so frequent access to these files is not recommended for normal program operation. The contents of these files are: _npc_ Next Program Counter - valid only when the SPU is in a stopped state. _decr_ SPU Decrementer _decr_status_ Decrementer Status _spu_tag_mask_ MFC tag mask for SPU DMA _event_mask_ Event mask for SPU interrupts _event_status_ Number of SPU events pending (read-only) _srr0_ Interrupt Return address register _lslr_ Local Store Limit Register The possible operations on these files are: [**read**(2)](https://www.chedong.com/phpMan.php/man/read/2/markdown) Reads the current register value. If the register value is larger than the buffer passed to the [**read**(2)](https://www.chedong.com/phpMan.php/man/read/2/markdown) system call, subsequent reads will continue read‐ ing from the same buffer, until the end of the buffer is reached. When a complete string has been read, all subsequent read operations will re‐ turn zero bytes and a new file descriptor needs to be opened to read a new value. [**write**(2)](https://www.chedong.com/phpMan.php/man/write/2/markdown) A [**write**(2)](https://www.chedong.com/phpMan.php/man/write/2/markdown) operation on the file sets the register to the value given in the string. The string is parsed from the beginning until the first nonnumeric character or the end of the buffer. Subsequent writes to the same file de‐ scriptor overwrite the previous setting. Except for the _npc_ file, these files are not present on contexts that have been created with the **SPU**___**CREATE**___**NOSCHED** flag. _/fpcr_ This file provides access to the Floating Point Status and Control Register (fcpr) as a binary, four-byte file. The operations on the _fpcr_ file are: [**read**(2)](https://www.chedong.com/phpMan.php/man/read/2/markdown) If _count_ is smaller than four, [**read**(2)](https://www.chedong.com/phpMan.php/man/read/2/markdown) returns -1 and sets _errno_ to **EINVAL**. Otherwise, a four-byte value is placed in the data buffer; this is the current value of the _fpcr_ register. [**write**(2)](https://www.chedong.com/phpMan.php/man/write/2/markdown) If _count_ is smaller than four, [**write**(2)](https://www.chedong.com/phpMan.php/man/write/2/markdown) returns -1 and sets _errno_ to **EINVAL**. Otherwise, a four-byte value is copied from the data buffer, updating the value of the _fpcr_ register. _/signal1_, _/signal2_ The files provide access to the two signal notification channels of an SPU. These are read-write files that operate on four-byte words. Writing to one of these files trig‐ gers an interrupt on the SPU. The value written to the signal files can be read from the SPU through a channel read or from host user space through the file. After the value has been read by the SPU, it is reset to zero. The possible operations on an open _signal1_ or _signal2_ file are: [**read**(2)](https://www.chedong.com/phpMan.php/man/read/2/markdown) If _count_ is smaller than four, [**read**(2)](https://www.chedong.com/phpMan.php/man/read/2/markdown) returns -1 and sets _errno_ to **EINVAL**. Otherwise, a four-byte value is placed in the data buffer; this is the current value of the specified signal notification register. [**write**(2)](https://www.chedong.com/phpMan.php/man/write/2/markdown) If _count_ is smaller than four, [**write**(2)](https://www.chedong.com/phpMan.php/man/write/2/markdown) returns -1 and sets _errno_ to **EINVAL**. Otherwise, a four-byte value is copied from the data buffer, updating the value of the specified signal notification register. The signal notification regis‐ ter will either be replaced with the input data or will be updated to the bit‐ wise OR operation of the old value and the input data, depending on the con‐ tents of the _signal1_type_ or _signal2_type_ files respectively. _/signal1_type_, _/signal2_type_ These two files change the behavior of the _signal1_ and _signal2_ notification files. They contain a numeric ASCII string which is read as either "1" or "0". In mode 0 (overwrite), the hardware replaces the contents of the signal channel with the data that is written to it. In mode 1 (logical OR), the hardware accumulates the bits that are subsequently written to it. The possible operations on an open _signal1_type_ or _signal2_type_ file are: [**read**(2)](https://www.chedong.com/phpMan.php/man/read/2/markdown) When the count supplied to the [**read**(2)](https://www.chedong.com/phpMan.php/man/read/2/markdown) call is shorter than the required length for the digit (plus a newline character), subsequent reads from the same file descriptor will complete the string. When a complete string has been read, all subsequent read operations will return zero bytes and a new file descriptor needs to be opened to read the value again. [**write**(2)](https://www.chedong.com/phpMan.php/man/write/2/markdown) A [**write**(2)](https://www.chedong.com/phpMan.php/man/write/2/markdown) operation on the file sets the register to the value given in the string. The string is parsed from the beginning until the first nonnumeric character or the end of the buffer. Subsequent writes to the same file de‐ scriptor overwrite the previous setting. _/mbox_info_, _/ibox_info_, _/wbox_info_, _/dma_into_, _/proxydma_info_ Read-only files that contain the saved state of the SPU mailboxes and DMA queues. This allows the SPU status to be inspected, mainly for debugging. The _mbox_info_ and _ibox_info_ files each contain the four-byte mailbox message that has been written by the SPU. If no message has been written to these mailboxes, then contents of these files is undefined. The _mbox_stat_, _ibox_stat_, and _wbox_stat_ files contain the avail‐ able message count. The _wbox_info_ file contains an array of four-byte mailbox messages, which have been sent to the SPU. With current CBEA machines, the array is four items in length, so up to 4 * 4 = 16 bytes can be read from this file. If any mailbox queue entry is empty, then the bytes read at the corresponding location are undefined. The _dma_info_ file contains the contents of the SPU MFC DMA queue, represented as the following structure: struct spu_dma_info { uint64_t dma_info_type; uint64_t dma_info_mask; uint64_t dma_info_status; uint64_t dma_info_stall_and_notify; uint64_t dma_info_atomic_command_status; struct mfc_cq_sr dma_info_command_data[16]; }; The last member of this data structure is the actual DMA queue, containing 16 entries. The _mfc_cq_sr_ structure is defined as: struct mfc_cq_sr { uint64_t mfc_cq_data0_RW; uint64_t mfc_cq_data1_RW; uint64_t mfc_cq_data2_RW; uint64_t mfc_cq_data3_RW; }; The _proxydma_info_ file contains similar information, but describes the proxy DMA queue (i.e., DMAs initiated by entities outside the SPU) instead. The file is in the fol‐ lowing format: struct spu_proxydma_info { uint64_t proxydma_info_type; uint64_t proxydma_info_mask; uint64_t proxydma_info_status; struct mfc_cq_sr proxydma_info_command_data[8]; }; Accessing these files requires that the SPU context is scheduled out - frequent use can be inefficient. These files should not be used for normal program operation. These files are not present on contexts that have been created with the **SPU**___**CRE**‐‐ **ATE**___**NOSCHED** flag. _/cntl_ This file provides access to the SPU Run Control and SPU status registers, as an ASCII string. The following operations are supported: [**read**(2)](https://www.chedong.com/phpMan.php/man/read/2/markdown) Reads from the _cntl_ file will return an ASCII string with the hex value of the SPU Status register. [**write**(2)](https://www.chedong.com/phpMan.php/man/write/2/markdown) Writes to the _cntl_ file will set the context's SPU Run Control register. _/mfc_ Provides access to the Memory Flow Controller of the SPU. Reading from the file re‐ turns the contents of the SPU's MFC Tag Status register, and writing to the file ini‐ tiates a DMA from the MFC. The following operations are supported: [**write**(2)](https://www.chedong.com/phpMan.php/man/write/2/markdown) Writes to this file need to be in the format of a MFC DMA command, defined as follows: struct mfc_dma_command { int32_t pad; /* reserved */ uint32_t lsa; /* local storage address */ uint64_t ea; /* effective address */ uint16_t size; /* transfer size */ uint16_t tag; /* command tag */ uint16_t class; /* class ID */ uint16_t cmd; /* command opcode */ }; Writes are required to be exactly _sizeof(struct_ _mfc_dma_command)_ bytes in size. The command will be sent to the SPU's MFC proxy queue, and the tag stored in the kernel (see below). [**read**(2)](https://www.chedong.com/phpMan.php/man/read/2/markdown) Reads the contents of the tag status register. If the file is opened in block‐ ing mode (i.e., without **O**___**NONBLOCK**), then the read will block until a DMA tag (as performed by a previous write) is complete. In nonblocking mode, the MFC tag status register will be returned without waiting. [**poll**(2)](https://www.chedong.com/phpMan.php/man/poll/2/markdown) Calling [**poll**(2)](https://www.chedong.com/phpMan.php/man/poll/2/markdown) on the _mfc_ file will block until a new DMA can be started (by checking for **POLLOUT**) or until a previously started DMA (by checking for **POLLIN**) has been completed. _/mss_ Provides access to the MFC MultiSource Synchronization (MSS) facility. By [**mmap**(2)](https://www.chedong.com/phpMan.php/man/mmap/2/markdown)-ing this file, processes can access the MSS area of the SPU. The following operations are supported: [**mmap**(2)](https://www.chedong.com/phpMan.php/man/mmap/2/markdown) Mapping **mss** into the process address space gives access to the SPU MSS area within the process address space. Only **MAP**___**SHARED** mappings are allowed. _/psmap_ Provides access to the whole problem-state mapping of the SPU. Applications can use this area to interface to the SPU, rather than writing to individual register files in **spufs**. The following operations are supported: [**mmap**(2)](https://www.chedong.com/phpMan.php/man/mmap/2/markdown) Mapping **psmap** gives a process a direct map of the SPU problem state area. Only **MAP**___**SHARED** mappings are supported. _/phys-id_ Read-only file containing the physical SPU number that the SPU context is running on. When the context is not running, this file contains the string "-1". The physical SPU number is given by an ASCII hex string. _/object-id_ Allows applications to store (or retrieve) a single 64-bit ID into the context. This ID is later used by profiling tools to uniquely identify the context. [**write**(2)](https://www.chedong.com/phpMan.php/man/write/2/markdown) By writing an ASCII hex value into this file, applications can set the object ID of the SPU context. Any previous value of the object ID is overwritten. [**read**(2)](https://www.chedong.com/phpMan.php/man/read/2/markdown) Reading this file gives an ASCII hex string representing the object ID for this SPU context. ## EXAMPLES _/etc/fstab_ entry none /spu spufs gid=spu 0 0 ## SEE ALSO [**close**(2)](https://www.chedong.com/phpMan.php/man/close/2/markdown), **spu**___**[create**(2)](https://www.chedong.com/phpMan.php/man/create/2/markdown), **spu**___**[run**(2)](https://www.chedong.com/phpMan.php/man/run/2/markdown), [**capabilities**(7)](https://www.chedong.com/phpMan.php/man/capabilities/7/markdown) _The_ _Cell_ _Broadband_ _Engine_ _Architecture_ _(CBEA)_ _specification_ ## COLOPHON This page is part of release 5.10 of the Linux _man-pages_ project. A description of the project, information about reporting bugs, and the latest version of this page, can be found at . Linux 2020-12-21 [SPUFS(7)](https://www.chedong.com/phpMan.php/man/SPUFS/7/markdown)