# phpman > man > libnetlink(3) [libnetlink(3)](https://www.chedong.com/phpMan.php/man/libnetlink/3/markdown) Library Functions Manual [libnetlink(3)](https://www.chedong.com/phpMan.php/man/libnetlink/3/markdown) ## NAME libnetlink - A library for accessing the netlink service ## SYNOPSIS #include #include #include #include int rtnl_open(struct rtnl_handle *rth, unsigned subscriptions) int rtnl_wilddump_request(struct rtnl_handle *rth, int family, int type) int rtnl_send(struct rtnl_handle *rth, char *buf, int len) int rtnl_dump_request(struct rtnl_handle *rth, int type, void *req, int len) int rtnl_dump_filter(struct rtnl_handle *rth, int (*filter)(struct sockaddr_nl *, struct nlmsghdr *n, void *), void *arg1, int (*junk)(struct sockaddr_nl *,struct nlmsghdr *n, void *), void *arg2) int rtnl_talk(struct rtnl_handle *rtnl, struct nlmsghdr *n, pid_t peer, unsigned groups, struct nlmsghdr *answer, int (*junk)(struct sockaddr_nl *,struct nlmsghdr *n, void *), void *jarg) int rtnl_listen(struct rtnl_handle *rtnl, int (*handler)(struct sockaddr_nl *, struct rtnl_ctrl_data *, struct nlmsghdr *n, void *), void *jarg) int rtnl_from_file(FILE *rtnl, int (*handler)(struct sockaddr_nl *,struct nlmsghdr *n, void *), void *jarg) int addattr32(struct nlmsghdr *n, int maxlen, int type, __u32 data) int addattr_l(struct nlmsghdr *n, int maxlen, int type, void *data, int alen) int rta_addattr32(struct rtattr *rta, int maxlen, int type, __u32 data) int rta_addattr_l(struct rtattr *rta, int maxlen, int type, void *data, int alen) ## DESCRIPTION libnetlink provides a higher level interface to [**rtnetlink**(7)](https://www.chedong.com/phpMan.php/man/rtnetlink/7/markdown). The read functions return 0 on success and a negative errno on failure. The send functions return the amount of data sent, or -1 on error. rtnl_open Open a rtnetlink socket and save the state into the **rth** handle. This handle is passed to all subsequent calls. **subscriptions** is a bitmap of the rtnetlink multicast groups the socket will be a member of. rtnl_wilddump_request Request a full dump of the **type** database for **family** addresses. **type** is a rtnetlink message type. rtnl_dump_request Request a full dump of the **type** data buffer into **buf** with maximum length of **len.** **type** is a rtnetlink message type. rtnl_dump_filter Receive netlink data after a request and filter it. The **filter** callback checks if the received message is wanted. It gets the source address of the message, the message it‐ self and **arg1** as arguments. 0 as return means that the filter passed, a negative value is returned by _rtnl_dump_filter_ in case of error. NULL for _filter_ means to not use a filter. **junk** is used to filter messages not destined to the local socket. Only one message bundle is received. If there is a message pending, this function does not block. rtnl_listen Receive netlink data after a request and pass it to _handler._ **handler** is a callback that gets the message source address, anscillary data, the message itself, and the **jarg** cookie as arguments. It will get called for all received messages. Only one mes‐ sage bundle is received. If there is a message pending this function does not block. rtnl_from_file Works like _rtnl_listen,_ but reads a netlink message bundle from the file **file** and passes the messages to **handler** for parsing. The file should contain raw data as re‐ ceived from a rtnetlink socket. The following functions are useful to construct custom rtnetlink messages. For simple data‐ base dumping with filtering it is better to use the higher level functions above. See **rt**‐‐ [**netlink**(3)](https://www.chedong.com/phpMan.php/man/netlink/3/markdown) and [**netlink**(3)](https://www.chedong.com/phpMan.php/man/netlink/3/markdown) on how to generate a rtnetlink message. The following utility func‐ tions require a continuous buffer that already contains a netlink message header and a rt‐ netlink request. rtnl_send Send the rtnetlink message in **buf** of length **len** to handle **rth.** addattr32 Add a __u32 attribute of type **type** and with value **data** to netlink message **n,** which is part of a buffer of length **maxlen.** addattr_l Add a variable length attribute of type **type** and with value **data** and **alen** length to netlink message **n,** which is part of a buffer of length **maxlen.** **data** is copied. rta_addattr32 Initialize the rtnetlink attribute **rta** with a __u32 data value. rta_addattr32 Initialize the rtnetlink attribute **rta** with a variable length data value. ## BUGS This library is meant for internal use, use libmnl for new programs. The functions sometimes use fprintf and exit when a fatal error occurs. This library should be named librtnetlink. ## AUTHORS netlink/rtnetlink was designed and written by Alexey Kuznetsov. Andi Kleen wrote the man page. ## SEE ALSO [**netlink**(7)](https://www.chedong.com/phpMan.php/man/netlink/7/markdown), [**rtnetlink**(7)](https://www.chedong.com/phpMan.php/man/rtnetlink/7/markdown) /usr/include/linux/rtnetlink.h [libnetlink(3)](https://www.chedong.com/phpMan.php/man/libnetlink/3/markdown)