libnl  1.1

Handle representing a netlink socket. More...

Allocation

struct nl_handle * nl_handle_alloc (void)
 Allocate new netlink socket handle. More...
 
struct nl_handle * nl_handle_alloc_cb (struct nl_cb *cb)
 Allocate new socket handle with custom callbacks. More...
 
void nl_handle_destroy (struct nl_handle *handle)
 Destroy netlink handle. More...
 

Sequence Numbers

void nl_disable_sequence_check (struct nl_handle *handle)
 Disable sequence number checking. More...
 
unsigned int nl_socket_use_seq (struct nl_handle *handle)
 Use next sequence number. More...
 

Source Idenficiation

uint32_t nl_socket_get_local_port (struct nl_handle *handle)
 
void nl_socket_set_local_port (struct nl_handle *handle, uint32_t port)
 Set local port of socket. More...
 

Group Subscriptions

int nl_socket_add_membership (struct nl_handle *handle, int group)
 Join a group. More...
 
int nl_socket_drop_membership (struct nl_handle *handle, int group)
 Leave a group. More...
 
void nl_join_groups (struct nl_handle *handle, int groups)
 Join multicast groups (deprecated) More...
 

Peer Identfication

uint32_t nl_socket_get_peer_port (struct nl_handle *handle)
 
void nl_socket_set_peer_port (struct nl_handle *handle, uint32_t port)
 

File Descriptor

int nl_socket_get_fd (struct nl_handle *handle)
 
int nl_socket_set_nonblocking (struct nl_handle *handle)
 Set file descriptor of socket handle to non-blocking state. More...
 
void nl_socket_enable_msg_peek (struct nl_handle *handle)
 Enable use of MSG_PEEK when reading from socket. More...
 
void nl_socket_disable_msg_peek (struct nl_handle *handle)
 Disable use of MSG_PEEK when reading from socket. More...
 

Callback Handler

struct nl_cb * nl_socket_get_cb (struct nl_handle *handle)
 
void nl_socket_set_cb (struct nl_handle *handle, struct nl_cb *cb)
 
int nl_socket_modify_cb (struct nl_handle *handle, enum nl_cb_type type, enum nl_cb_kind kind, nl_recvmsg_msg_cb_t func, void *arg)
 Modify the callback handler associated to the socket. More...
 

Utilities

int nl_set_buffer_size (struct nl_handle *handle, int rxbuf, int txbuf)
 Set socket buffer size of netlink handle. More...
 
int nl_set_passcred (struct nl_handle *handle, int state)
 Enable/disable credential passing on netlink handle. More...
 
int nl_socket_recv_pktinfo (struct nl_handle *handle, int state)
 Enable/disable receival of additional packet information. More...
 

Detailed Description

The socket is represented in a structure called the netlink handle, besides the socket, it stores various settings and values related to the socket. Every socket handle has a mandatory association with a set of callbacks which can be used to modify the behaviour when sending/receiving data from the socket.

Socket Attributes
  • Local Port: The local port is a netlink port identifying the local endpoint. It is used as source address for outgoing messages and will be addressed in replies. It must therefore be unique among all userspace applications. When the socket handle is allocated, a unique port number is generated automatically in the form of 22 bits Process Identifier + 10 bits Arbitary Number. Therefore the library is capable of generating 1024 unique local port numbers for every process. If more sockets are required, the application has to manage port numbers itself using nl_socket_set_local_port().
  • Group Subscriptions: A socket can subscribe to any number of multicast groups. It will then receive a copy of all messages sent to one of the groups. This method is mainly used for event notification. Prior to kernel 2.6.14, the group subscription was done via bitmask which limited to a total number of groups of 32. With 2.6.14 a new method was added based on continous identifiers which supports an arbitary number of groups. Both methods are supported, see nl_join_groups() respectively nl_socket_add_membership() and nl_socket_drop_membership().
  • Peer Port: The peer port is a netlink port identifying the peer's endpoint. If no peer port is specified, the kernel will try to autobind to a socket of the specified netlink family automatically. This is very common as typically only one listening socket exists on the kernel side. The peer port can be modified using nl_socket_set_peer_port().
  • Peer Groups:
  • File Descriptor: The file descriptor of the socket, it can be accessed via nl_socket_get_fd() to change socket options or monitor activity using poll()/select().
  • Protocol: Once connected, the socket is bound to stick to one netlink family. This field is invisible, it is maintained automatically. (See nl_connect())
  • Next Sequence Number: Next available sequence number to be used for the next message being sent out. (Initial value: UNIX time when the socket was allocated.) Sequence numbers can be used via nl_socket_use_seq().
  • Expected Sequence Number: Expected sequence number in the next message received from the socket. (Initial value: Equal to next sequence number.)
  • Callbacks Configuration:
1) Creating the netlink handle
struct nl_handle *handle;
// Allocate and initialize a new netlink handle
handle = nl_handle_alloc();
// Use nl_socket_get_fd() to fetch the file description, for example to
// put a socket into non-blocking i/o mode.
fcntl(nl_socket_get_fd(handle), F_SETFL, O_NONBLOCK);
2) Group Subscriptions
// Event notifications are typically sent to multicast addresses which
// represented by groups. Join a group to f.e. receive link notifications.
nl_socket_add_membership(handle, RTNLGRP_LINK);
6) Cleaning up
// Finally destroy the netlink handle

Function Documentation

struct nl_handle* nl_handle_alloc ( void  )
read
Returns
Newly allocated netlink socket handle or NULL.

Definition at line 206 of file socket.c.

References nl_cb_alloc().

207 {
208  struct nl_cb *cb;
209 
210  cb = nl_cb_alloc(default_cb);
211  if (!cb) {
212  nl_errno(ENOMEM);
213  return NULL;
214  }
215 
216  return __alloc_handle(cb);
217 }
struct nl_handle* nl_handle_alloc_cb ( struct nl_cb *  cb)
read
Parameters
cbCallback handler

The reference to the callback handler is taken into account automatically, it is released again upon calling nl_handle_destroy().

Returns
Newly allocted socket handle or NULL.

Definition at line 228 of file socket.c.

229 {
230  if (cb == NULL)
231  BUG();
232 
233  return __alloc_handle(nl_cb_get(cb));
234 }
void nl_handle_destroy ( struct nl_handle *  handle)
Parameters
handleNetlink handle.

Definition at line 240 of file socket.c.

Referenced by nl_cache_mngr_free().

241 {
242  if (!handle)
243  return;
244 
245  if (handle->h_fd >= 0)
246  close(handle->h_fd);
247 
248  if (!(handle->h_flags & NL_OWN_PORT))
249  release_local_port(handle->h_local.nl_pid);
250 
251  nl_cb_put(handle->h_cb);
252  free(handle);
253 }
void nl_disable_sequence_check ( struct nl_handle *  handle)
Parameters
handleNetlink handle.

Disables checking of sequence numbers on the netlink handle. This is required to allow messages to be processed which were not requested by a preceding request message, e.g. netlink events.

Note
This function modifies the NL_CB_SEQ_CHECK configuration in the callback handle associated with the socket.

Definition at line 279 of file socket.c.

References NL_CB_CUSTOM, NL_CB_SEQ_CHECK, and nl_cb_set().

Referenced by nl_cache_mngr_alloc().

280 {
281  nl_cb_set(handle->h_cb, NL_CB_SEQ_CHECK,
282  NL_CB_CUSTOM, noop_seq_check, NULL);
283 }
unsigned int nl_socket_use_seq ( struct nl_handle *  handle)
Parameters
handleNetlink handle

Uses the next available sequence number and increases the counter by one for subsequent calls.

Returns
Unique serial sequence number

Definition at line 294 of file socket.c.

295 {
296  return handle->h_seq_next++;
297 }
void nl_socket_set_local_port ( struct nl_handle *  handle,
uint32_t  port 
)
Parameters
handleNetlink handle
portLocal port identifier

Assigns a local port identifier to the socket. If port is 0 a unique port identifier will be generated automatically.

Definition at line 319 of file socket.c.

320 {
321  if (port == 0) {
322  port = generate_local_port();
323  handle->h_flags &= ~NL_OWN_PORT;
324  } else {
325  if (!(handle->h_flags & NL_OWN_PORT))
326  release_local_port(handle->h_local.nl_pid);
327  handle->h_flags |= NL_OWN_PORT;
328  }
329 
330  handle->h_local.nl_pid = port;
331 }
int nl_socket_add_membership ( struct nl_handle *  handle,
int  group 
)
Parameters
handleNetlink handle
groupGroup identifier

Joins the specified group using the modern socket option which is available since kernel version 2.6.14. It allows joining an almost arbitary number of groups without limitation.

Make sure to use the correct group definitions as the older bitmask definitions for nl_join_groups() are likely to still be present for backward compatibility reasons.

Returns
0 on sucess or a negative error code.

Definition at line 355 of file socket.c.

Referenced by nl_cache_mngr_add().

356 {
357  int err;
358 
359  if (handle->h_fd == -1)
360  return nl_error(EBADFD, "Socket not connected");
361 
362  err = setsockopt(handle->h_fd, SOL_NETLINK, NETLINK_ADD_MEMBERSHIP,
363  &group, sizeof(group));
364  if (err < 0)
365  return nl_error(errno, "setsockopt(NETLINK_ADD_MEMBERSHIP) "
366  "failed");
367 
368  return 0;
369 }
int nl_socket_drop_membership ( struct nl_handle *  handle,
int  group 
)
Parameters
handleNetlink handle
groupGroup identifier

Leaves the specified group using the modern socket option which is available since kernel version 2.6.14.

See Also
nl_socket_add_membership
Returns
0 on success or a negative error code.

Definition at line 382 of file socket.c.

Referenced by nl_cache_mngr_add().

383 {
384  int err;
385 
386  if (handle->h_fd == -1)
387  return nl_error(EBADFD, "Socket not connected");
388 
389  err = setsockopt(handle->h_fd, SOL_NETLINK, NETLINK_DROP_MEMBERSHIP,
390  &group, sizeof(group));
391  if (err < 0)
392  return nl_error(errno, "setsockopt(NETLINK_DROP_MEMBERSHIP) "
393  "failed");
394 
395  return 0;
396 }
void nl_join_groups ( struct nl_handle *  handle,
int  groups 
)
Parameters
handleNetlink handle.
groupsBitmask of groups to join.

This function defines the old way of joining multicast group which has to be done prior to calling nl_connect(). It works on any kernel version but is very limited as only 32 groups can be joined.

Definition at line 407 of file socket.c.

408 {
409  handle->h_local.nl_groups |= groups;
410 }
int nl_socket_set_nonblocking ( struct nl_handle *  handle)
Parameters
handleNetlink socket
Returns
0 on success or a negative error code.

Definition at line 448 of file socket.c.

Referenced by nl_cache_mngr_alloc().

449 {
450  if (handle->h_fd == -1)
451  return nl_error(EBADFD, "Socket not connected");
452 
453  if (fcntl(handle->h_fd, F_SETFL, O_NONBLOCK) < 0)
454  return nl_error(errno, "fcntl(F_SETFL, O_NONBLOCK) failed");
455 
456  return 0;
457 }
void nl_socket_enable_msg_peek ( struct nl_handle *  handle)
Parameters
handleNetlink socket

Definition at line 463 of file socket.c.

464 {
465  handle->h_flags |= NL_MSG_PEEK;
466 }
void nl_socket_disable_msg_peek ( struct nl_handle *  handle)
Parameters
handleNetlink socket

Definition at line 472 of file socket.c.

473 {
474  handle->h_flags &= ~NL_MSG_PEEK;
475 }
int nl_socket_modify_cb ( struct nl_handle *  handle,
enum nl_cb_type  type,
enum nl_cb_kind  kind,
nl_recvmsg_msg_cb_t  func,
void *  arg 
)
Parameters
handlenetlink handle
typewhich type callback to set
kindkind of callback
funccallback function
argargument to be passwd to callback function
See Also
nl_cb_set

Definition at line 505 of file socket.c.

References nl_cb_set().

Referenced by nl_cache_mngr_alloc().

508 {
509  return nl_cb_set(handle->h_cb, type, kind, func, arg);
510 }
int nl_set_buffer_size ( struct nl_handle *  handle,
int  rxbuf,
int  txbuf 
)
Parameters
handleNetlink handle.
rxbufNew receive socket buffer size in bytes.
txbufNew transmit socket buffer size in bytes.

Sets the socket buffer size of a netlink handle to the specified values rxbuf and txbuf. Providing a value of 0 assumes a good default value.

Note
It is not required to call this function prior to nl_connect().
Returns
0 on sucess or a negative error code.

Definition at line 532 of file socket.c.

Referenced by nl_connect().

533 {
534  int err;
535 
536  if (rxbuf <= 0)
537  rxbuf = 32768;
538 
539  if (txbuf <= 0)
540  txbuf = 32768;
541 
542  if (handle->h_fd == -1)
543  return nl_error(EBADFD, "Socket not connected");
544 
545  err = setsockopt(handle->h_fd, SOL_SOCKET, SO_SNDBUF,
546  &txbuf, sizeof(txbuf));
547  if (err < 0)
548  return nl_error(errno, "setsockopt(SO_SNDBUF) failed");
549 
550  err = setsockopt(handle->h_fd, SOL_SOCKET, SO_RCVBUF,
551  &rxbuf, sizeof(rxbuf));
552  if (err < 0)
553  return nl_error(errno, "setsockopt(SO_RCVBUF) failed");
554 
555  handle->h_flags |= NL_SOCK_BUFSIZE_SET;
556 
557  return 0;
558 }
int nl_set_passcred ( struct nl_handle *  handle,
int  state 
)
Parameters
handleNetlink handle
stateNew state (0 - disabled, 1 - enabled)
Returns
0 on success or a negative error code

Definition at line 567 of file socket.c.

568 {
569  int err;
570 
571  if (handle->h_fd == -1)
572  return nl_error(EBADFD, "Socket not connected");
573 
574  err = setsockopt(handle->h_fd, SOL_SOCKET, SO_PASSCRED,
575  &state, sizeof(state));
576  if (err < 0)
577  return nl_error(errno, "setsockopt(SO_PASSCRED) failed");
578 
579  if (state)
580  handle->h_flags |= NL_SOCK_PASSCRED;
581  else
582  handle->h_flags &= ~NL_SOCK_PASSCRED;
583 
584  return 0;
585 }
int nl_socket_recv_pktinfo ( struct nl_handle *  handle,
int  state 
)
Parameters
handleNetlink handle
stateNew state (0 - disabled, 1 - enabled)
Returns
0 on success or a negative error code

Definition at line 594 of file socket.c.

595 {
596  int err;
597 
598  if (handle->h_fd == -1)
599  return nl_error(EBADFD, "Socket not connected");
600 
601  err = setsockopt(handle->h_fd, SOL_NETLINK, NETLINK_PKTINFO,
602  &state, sizeof(state));
603  if (err < 0)
604  return nl_error(errno, "setsockopt(NETLINK_PKTINFO) failed");
605 
606  return 0;
607 }