| NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | VERSIONS | CONFORMING TO | SEE ALSO | COLOPHON | The Linux Programming Interface |
RECVMMSG(2) Linux Programmer's Manual RECVMMSG(2)
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; /* Message header */
unsigned int msg_len; /* Number of received bytes for header */
};
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_WAITFORONE
Turns 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.
(This interval will be rounded up to the system clock granularity, and
kernel scheduling delays mean that the blocking interval may overrun by a
small amount.) 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:
EINVAL timeout is invalid.
The recvmmsg() system call was added in Linux 2.6.32. Support in glibc was
added in version 2.12.
recvmmsg() is Linux-specific.
clock_gettime(2), recvmsg(2), sendmmsg(2), sendmsg(2), socket(2), socket(7)
This page is part of release 3.41 of the Linux man-pages project. A
description of the project, and information about reporting bugs, can be
found at http://www.kernel.org/doc/man-pages/.
Linux 2012-05-02 RECVMMSG(2)
HTML rendering created 2012-05-11 by Michael Kerrisk,
author of
The Linux Programming Interface,
maintainer of the
Linux man-pages project