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NetBSD 6.1.5 - man page for accept (netbsd section 2)

ACCEPT(2)			     BSD System Calls Manual				ACCEPT(2)

     accept, paccept -- accept a connection on a socket

     Standard C Library (libc, -lc)

     #include <sys/socket.h>

     accept(int s, struct sockaddr * restrict addr, socklen_t * restrict addrlen);

     paccept(int s, struct sockaddr * restrict addr, socklen_t * restrict addrlen,
	 const sigset_t * restrict sigmask, int flags);

     The argument s is a socket that has been created with socket(2), bound to an address with
     bind(2), and is listening for connections after a listen(2).  The accept() argument extracts
     the first connection request on the queue of pending connections, creates a new socket with
     the same properties of s and allocates a new file descriptor for the socket.  If no pending
     connections are present on the queue, and the socket is not marked as non-blocking, accept()
     blocks the caller until a connection is present.  If the socket is marked non-blocking and
     no pending connections are present on the queue, accept() returns an error as described
     below.  The accepted socket may not be used to accept more connections.  The original socket
     s remains open.

     The argument addr is a result parameter that is filled in with the address of the connecting
     entity, as known to the communications layer.  The exact format of the addr parameter is
     determined by the domain in which the communication is occurring.	The addrlen is a value-
     result parameter; it should initially contain the amount of space pointed to by addr; on
     return it will contain the actual length (in bytes) of the address returned.  This call is
     used with connection-based socket types, currently with SOCK_STREAM.

     It is possible to select(2) or poll(2) a socket for the purposes of doing an accept() by
     selecting or polling it for read.

     For certain protocols which require an explicit confirmation, such as ISO or DATAKIT,
     accept() can be thought of as merely dequeuing the next connection request and not implying
     confirmation.  Confirmation can be implied by a normal read or write on the new file
     descriptor, and rejection can be implied by closing the new socket.

     One can obtain user connection request data without confirming the connection by issuing a
     recvmsg(2) call with an msg_iovlen of 0 and a non-zero msg_controllen, or by issuing a
     getsockopt(2) request.  Similarly, one can provide user connection rejection information by
     issuing a sendmsg(2) call with providing only the control information, or by calling

     The paccept() function behaves exactly like accept(), but it also allows to set the follow-
     ing flags on the returned file descriptor:

	   SOCK_CLOEXEC Set the close on exec property.
	   SOCK_NONBLOCK Sets non-blocking I/O.

     It can also temporarily replace the signal mask of the calling thread if sigmask is a
     non-NULL pointer, then the paccept() function shall replace the signal mask of the caller by
     the set of signals pointed to by sigmask before waiting for a connection, and shall restore
     the signal mask of the calling thread before returning.

     The accept() and paccept() calls return -1 on error.  If they succeed, they return a non-
     negative integer that is a descriptor for the accepted socket.

     The accept() implementation makes the new file descriptor inherit file flags (like
     O_NONBLOCK) from the listening socket.  It's a traditional behaviour for BSD derivative sys-
     tems.  On the other hand, there are implementations which don't do so.  Linux is an example
     of such implementations.  Portable programs should not rely on either of the behaviours.

     The accept() will fail if:

     [EAGAIN]		The socket is marked non-blocking and no connections are present to be

     [EBADF]		The descriptor is invalid.

     [ECONNABORTED]	A connection has been aborted.

     [EFAULT]		The addr parameter is not in a writable part of the user address space.

     [EINTR]		The accept() call has been interrupted by a signal.

     [EINVAL]		The socket has not been set up to accept connections (using bind(2) and

     [EMFILE]		The per-process descriptor table is full.

     [ENFILE]		The system file table is full.

     [ENOTSOCK] 	The descriptor references a file, not a socket.

     [EOPNOTSUPP]	The referenced socket is not of type SOCK_STREAM.

     bind(2), connect(2), listen(2), poll(2), select(2), socket(2)

     The accept() function appeared in 4.2BSD.	The pselect() function is inspired from Linux and
     appeared in NetBSD 6.0.

BSD					   June 2, 2011 				      BSD

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