Reference

connectat(2)

initiate a connection on a socket

NAME

connectat – initiate a connection on a socket

LIBRARY

Standard C Library (libc, -lc)

SYNOPSIS

#include <sys/types.h>

#include <sys/socket.h>

#include <fcntl.h>

int

connectat(int fd, int s, const struct sockaddr *name, socklen_t namelen);

DESCRIPTION

The connectat() system call initiates a connection on the socket s. When passed the special value AT_FDCWD in the fd parameter, the behavior is identical to a call to connect(2). Otherwise, connectat() works like the connect(2) system call with two exceptions:

  1. It is limited to sockets in the PF_LOCAL domain.

  2. If the file path stored in the sun_path field of the sockaddr_un structure is a relative path, it is located relative to the directory associated with the file descriptor fd.

  3. If the sun_path field is empty, that is, namelen equals offsetof(struct sockaddr_un, sun_path), then fd does not resolve a path but instead names the peer socket directly.

    The descriptor may be the peer socket itself, or a descriptor for a file, such as an O_PATH handle opened with open(2). In the latter case, the O_PATH file description may point either to a traditional socket file bound to the peer, or to a /dev/fd/N node. The /dev/fd/N node must name the socket descriptor itself; the named descriptor is resolved a single level and not chased further. With a standard fdescfs(5) mount this means a node naming a traditional socket file, or another /dev/fd/N node, does not resolve to a peer.

    In all cases, fd must carry the CAP_CONNECTAT capability right, and the target of a /dev/fd/N node must also carry that right; see unix(4) for the details of this form.

RETURN VALUES

The connectat() function returns the value 0 if successful; otherwise the value -1 is returned and the global variable errno is set to indicate the error.

ERRORS

The connectat() system call may fail with the same errors as the connect(2) system call or with the following errors:

[EBADF]

The sun_path field does not specify an absolute path and the fd argument is neither AT_FDCWD nor a valid file descriptor.

[ENOTDIR]

The sun_path field is not an absolute path and fd is neither AT_FDCWD nor a file descriptor associated with a directory.

[EINVAL]

The sun_path field is empty but fd is AT_FDCWD, so no descriptor names the peer.

SEE ALSO

bindat(2), connect(2), socket(2), unix(4)

AUTHORS

The connectat was developed by Pawel Jakub Dawidek ⟨[email protected]⟩ under sponsorship from the FreeBSD Foundation.

History