libnetlink(3)

🧚 libnetlink(3) 🧚

✨ NAME ✨

libnetlink 💖 okay so this is a library for talking to the netlink service 🦋

📜 SYNOPSIS 📜

#include <asm/types.h>
#include <libnetlink.h>
#include <linux/netlink.h>
#include <linux/rtnetlink.h>

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 💅

okay so libnetlink gives you a higher level interface to rtnetlink(7) 🫶 bestie, the read functions return 0 on success and a negative errno on failure 😭 and the send functions return the amount of data sent, or -1 on error ✨

• rtnl_open — opens a rtnetlink socket and saves the state into the rth handle 🦋 that handle gets passed to every call after this one. subscriptions is a bitmap of the rtnetlink multicast groups the socket will be a member of 💜
• rtnl_wilddump_request — requests a full dump of the type database for family addresses 🌸 type is a rtnetlink message type.
• rtnl_dump_request — requests a full dump of the type data into buf, with a max length of len 🍓 type is a rtnetlink message type.
• rtnl_dump_filter — receives netlink data after a request and filters it 🔥 the filter callback checks whether the received message is wanted. It gets the source address of the message, the message itself, and arg1 as arguments. A return of 0 means the filter passed, and a negative value is returned by rtnl_dump_filter if something goes wrong. Passing NULL for filter means no filter at all 🙈 junk is used to filter out messages that aren't meant for the local socket. Only one message bundle gets received, and if a message is pending, this function does not block 🫶
• rtnl_listen — receives netlink data after a request and passes it to handler 👑 the handler is a callback that gets the message source address, the ancillary data, the message itself, and the jarg cookie as arguments. It gets called for all received messages ✨ Only one message bundle is received, and if a message is 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 received from a rtnetlink socket.

🚨 bestie, the next bit is for when you want to build your own rtnetlink messages. For simple database dumping with filtering, just use the higher level functions above 💀 See rtnetlink(3) and netlink(3) to learn how to generate a rtnetlink message. These utility functions need a continuous buffer that already holds a netlink message header and a rtnetlink request.

• rtnl_send — sends the rtnetlink message in buf (length len) to the handle rth 🧚
• addattr32 — adds a __u32 attribute of type type with the value data to the netlink message n, which lives in a buffer of length maxlen 💜
• addattr_l — adds a variable length attribute of type type with the value data and length alen to the netlink message n, which lives in a buffer of length maxlen 🎀 data gets copied.
• rta_addattr32 — initializes the rtnetlink attribute rta with a __u32 data value 🦋
• rta_addattr32 — initializes the rtnetlink attribute rta with a variable length data value 🌸

🙈 BUGS 🙈

Warning, bestie: this library is meant for internal use only 😭 use libmnl for new programs.

The functions sometimes use fprintf and exit when a fatal error happens 💀 and this library should honestly be named librtnetlink 🥺

🫶 AUTHORS 🫶

netlink/rtnetlink was designed and written by Alexey Kuznetsov ✨ Andi Kleen wrote the man page 💖

🔗 SEE ALSO 🔗

• netlink(7), rtnetlink(7)
• /usr/include/linux/rtnetlink.h

okay bestie, that's the whole tea 🍵 this was libnetlink(3) from the Library Functions Manual, and that's a wrap 💅🌈