recvmmsg — receive multiple messages on a socket
#define _GNU_SOURCE #include <sys/socket.h>
int
recvmmsg( |
int sockfd, |
| struct mmsghdr *msgvec, | |
| unsigned int vlen, | |
| unsigned int flags, | |
struct timespec *timeout); |
The recvmmsg() system call
is an extension of recvmsg(2) that allows the
caller to receive multiple messages from a socket using a
single system call. (This has performance benefits for some
applications.) A further extension over recvmsg(2) is support for a
timeout on the receive operation.
The sockfd
argument is the file descriptor of the socket to receive data
from.
The msgvec
argument is a pointer to an array of mmsghdr structures. The size of this
array is specified in vlen.
The mmsghdr structure is
defined in <sys/socket.h> as:
struct mmsghdr { struct msghdr msg_hdr;unsigned int msg_len;};
The msg_hdr field
is a msghdr
structure, as described in recvmsg(2). The msg_len field is the number of
bytes returned for the message in the entry. This field has
the same value as the return value of a single recvmsg(2) on the
header.
The flags argument
contains flags ORed together. The flags are the same as
documented for recvmsg(2), with the
following addition:
MSG_WAITFORONETurns on MSG_DONTWAIT
after the first message has been received.
The timeout
argument points to a struct
timespec (see clock_gettime(2)) defining
a timeout (seconds plus nanoseconds) for the receive
operation. If timeout
is NULL then the operation
blocks indefinitely.
A blocking recvmmsg() call
blocks until vlen
messages have been received or until the timeout expires. A
nonblocking call reads as many messages as are available (up
to the limit specified by vlen) and returns
immediately.
On return from recvmmsg(),
successive elements of msgvec are updated to contain
information about each received message: msg_len contains the size of
the received message; the subfields of msg_hdr are updated as
described in recvmsg(2). The return
value of the call indicates the number of elements of
msgvec that have been
updated.
On success, recvmmsg()
returns the number of messages received in msgvec; on error, −1 is
returned, and errno is set to
indicate the error.
Errors are as for recvmsg(2). In addition, the following error can occur:
timeout is
invalid.
The recvmmsg() system call
was added in Linux 2.6.32. Support in glibc was added in
version 2.12.
This page is part of release 3.35 of the Linux man-pages project. A
description of the project, and information about reporting
bugs, can be found at http://man7.org/linux/man-pages/.
|
Copyright (C) 2011 by Andi Kleen <andifirstfloor.org> and Copyright (c) 2011 by Michael Kerrisk <mtk.manpagesgmail.com> Permission is granted to make and distribute verbatim copies of this manual provided the copyright notice and this permission notice are preserved on all copies. Permission is granted to copy and distribute modified versions of this manual under the conditions for verbatim copying, provided that the entire resulting derived work is distributed under the terms of a permission notice identical to this one. Since the Linux kernel and libraries are constantly changing, this manual page may be incorrect or out-of-date. The author(s) assume no responsibility for errors or omissions, or for damages resulting from the use of the information contained herein. The author(s) may not have taken the same level of care in the production of this manual, which is licensed free of charge, as they might when working professionally. Formatted or processed versions of this manual, if unaccompanied by the source, must acknowledge the copyright and authors of this work. |