socket(3)

📦
version 1.0.5 · 2 versions
, in debian trixie, ubuntu noble, ubuntu questing

✨ NAME ✨

socket — Netlink socket helpers 💖

okay so bestie, this is socket(3) from the libmnl Library Functions Manual, and it's basically your whole starter pack for talking to Netlink sockets. No cap. Let's get into it 🫶

🌸 SYNOPSIS 🌸

💅 Functions

int mnl_socket_get_fd (const struct mnl_socket *nl)
unsigned int mnl_socket_get_portid (const struct mnl_socket *nl)
struct mnl_socket * mnl_socket_open (int bus)
struct mnl_socket * mnl_socket_open2 (int bus, int flags)
struct mnl_socket * mnl_socket_fdopen (int fd)
int mnl_socket_bind (struct mnl_socket *nl, unsigned int groups, pid_t pid)
ssize_t mnl_socket_sendto (const struct mnl_socket *nl, const void *buf, size_t len)
ssize_t mnl_socket_recvfrom (const struct mnl_socket *nl, void *buf, size_t bufsiz)
int mnl_socket_close (struct mnl_socket *nl)
int mnl_socket_setsockopt (const struct mnl_socket *nl, int type, void *buf, socklen_t len)
int mnl_socket_getsockopt (const struct mnl_socket *nl, int type, void *buf, socklen_t *len)

🦋 Detailed Description 🦋

not me checking this section three times… it's empty, bestie 😭 the page literally just has the heading and then moves straight on to the function docs. it's giving minimalist. we respect it 💅

👑 Function Documentation 👑

int mnl_socket_bind (struct mnl_socket * nl, unsigned int groups, pid_t pid)

mnl_socket_bind — bind netlink socket 🔗

Parameters

  • nl — netlink socket obtained via mnl_socket_open()
  • groups — the group of message you're interested in
  • pid — the port ID you want to use (use zero for automatic selection)

On error, this function returns -1 and errno is appropriately set. On success, 0 is returned. You can use MNL_SOCKET_AUTOPID which is 0 for automatic port ID selection. ✨

Definition at line 193 of file socket.c.

int mnl_socket_close (struct mnl_socket * nl)

mnl_socket_close — close a given netlink socket 🚪

Parameters

  • nl — netlink socket obtained via mnl_socket_open()

On error, this function returns -1 and errno is appropriately set. On success, it returns 0.

Definition at line 296 of file socket.c.

struct mnl_socket * mnl_socket_fdopen (int fd)

mnl_socket_fdopen — associates a mnl_socket object with pre-existing socket. 🧷

Parameters

  • fd — pre-existing socket descriptor.

On error, it returns NULL and errno is appropriately set. Otherwise, it returns a valid pointer to the mnl_socket structure. It also sets the portID if the socket fd is already bound and it is AF_NETLINK.

heads up bestie: note that mnl_socket_get_portid() returns 0 if this function is used with non-netlink socket. 💀

Definition at line 161 of file socket.c.

int mnl_socket_get_fd (const struct mnl_socket * nl)

mnl_socket_get_fd — obtain file descriptor from netlink socket 🎟️

Parameters

  • nl — netlink socket obtained via mnl_socket_open()

This function returns the file descriptor of a given netlink socket.

Definition at line 85 of file socket.c.

unsigned int mnl_socket_get_portid (const struct mnl_socket * nl)

mnl_socket_get_portid — obtain Netlink PortID from netlink socket 🆔

Parameters

  • nl — netlink socket obtained via mnl_socket_open()

This function returns the Netlink PortID of a given netlink socket. It's a common mistake to assume that this PortID equals the process ID which is not always true. This is the case if you open more than one socket that is binded to the same Netlink subsystem from the same process. 🙈

Definition at line 99 of file socket.c.

int mnl_socket_getsockopt (const struct mnl_socket * nl, int type, void * buf, socklen_t * len)

mnl_socket_getsockopt — get a Netlink socket option ⚙️

Parameters

  • nl — netlink socket obtained via mnl_socket_open()
  • type — type of Netlink socket options
  • buf — pointer to the buffer to store the value of this option
  • len — size of the information written in the buffer

On error, this function returns -1 and errno is appropriately set.

Definition at line 343 of file socket.c.

struct mnl_socket * mnl_socket_open (int bus)

mnl_socket_open — open a netlink socket 🫧

Parameters

  • bus — the netlink socket bus ID (see NETLINK_* constants)

On error, it returns NULL and errno is appropriately set. Otherwise, it returns a valid pointer to the mnl_socket structure.

Definition at line 128 of file socket.c.

struct mnl_socket * mnl_socket_open2 (int bus, int flags)

mnl_socket_open2 — open a netlink socket with appropriate flags 🚩

Parameters

  • bus — the netlink socket bus ID (see NETLINK_* constants)
  • flags — the netlink socket flags (see SOCK_* constants in socket(2))

This is similar to mnl_socket_open(), but allows one to set flags like SOCK_CLOEXEC at socket creation time (useful for multi-threaded programs performing exec calls). 🔥

On error, it returns NULL and errno is appropriately set. Otherwise, it returns a valid pointer to the mnl_socket structure.

Definition at line 145 of file socket.c.

ssize_t mnl_socket_recvfrom (const struct mnl_socket * nl, void * buf, size_t bufsiz)

mnl_socket_recvfrom — receive a netlink message 📥

Parameters

  • nl — netlink socket obtained via mnl_socket_open()
  • buf — buffer that you want to use to store the netlink message
  • bufsiz — size of the buffer passed to store the netlink message

On error, it returns -1 and errno is appropriately set. If errno is set to ENOSPC, it means that the buffer that you have passed to store the netlink message is too small, so you have received a truncated message. To avoid this, you have to allocate a buffer of MNL_SOCKET_BUFFER_SIZE (which is 8KB, see linux/netlink.h for more information). Using this buffer size ensures that your buffer is big enough to store the netlink message without truncating it. 💅

bestie please actually size your buffer, ENOSPC truncation is not the moment 😭

Definition at line 256 of file socket.c.

ssize_t mnl_socket_sendto (const struct mnl_socket * nl, const void * buf, size_t len)

mnl_socket_sendto — send a netlink message of a certain size 📤

Parameters

  • nl — netlink socket obtained via mnl_socket_open()
  • buf — buffer containing the netlink message to be sent
  • len — number of bytes in the buffer that you want to send

On error, it returns -1 and errno is appropriately set. Otherwise, it returns the number of bytes sent. ✨

Definition at line 232 of file socket.c.

int mnl_socket_setsockopt (const struct mnl_socket * nl, int type, void * buf, socklen_t len)

mnl_socket_setsockopt — set Netlink socket option 🛠️

Parameters

  • nl — netlink socket obtained via mnl_socket_open()
  • type — type of Netlink socket options
  • buf — the buffer that contains the data about this option
  • len — the size of the buffer passed

This function allows you to set some Netlink socket option. As of writing this (see linux/netlink.h), the existing options are:

#define NETLINK_ADD_MEMBERSHIP  1
#define NETLINK_DROP_MEMBERSHIP 2
#define NETLINK_PKTINFO         3
#define NETLINK_BROADCAST_ERROR 4
#define NETLINK_NO_ENOBUFS      5

In the early days, Netlink only supported 32 groups expressed in a 32-bits mask. However, since 2.6.14, Netlink may have up to 2^32 multicast groups but you have to use setsockopt() with NETLINK_ADD_MEMBERSHIP to join a given multicast group. This function internally calls setsockopt() to join a given netlink multicast group. You can still use mnl_bind() and the 32-bit mask to join a set of Netlink multicast groups.

On error, this function returns -1 and errno is appropriately set.

Definition at line 328 of file socket.c.

🎀 Author 🎀

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okay that's the whole page, bestie, you ate it up 👑💖 kisses from libmnl Version 1.0.5, page socket(3) — no date on the footer so don't come for me, and the whole thing was generated automatically by Doxygen for libmnl straight from the source code. slay, go bind a socket 🦋✨

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