+++ /dev/null
-.\" Copyright (c) 2012 by Michael Kerrisk <mtk.manpages@gmail.com>
-.\" with some material from a draft by
-.\" Stephan Mueller <stephan.mueller@atsec.com>
-.\" in turn based on Andi Kleen's recvmmsg.2 page.
-.\"
-.\" %%%LICENSE_START(VERBATIM)
-.\" 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-.\" manual page may be incorrect or out-of-date.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.
-.\" %%%LICENSE_END
-.\"
-.TH SENDMMSG 2 2014-07-08 "Linux" "Linux Programmer's Manual"
-.SH NAME
-sendmmsg \- send multiple messages on a socket
-.SH SYNOPSIS
-.nf
-.BR "#define _GNU_SOURCE" " /* See feature_test_macros(7) */"
-.BI "#include <sys/socket.h>"
-
-.BI "int sendmmsg(int " sockfd ", struct mmsghdr *" msgvec \
-", unsigned int " vlen ","
-.BI " unsigned int " flags ");"
-.fi
-.SH DESCRIPTION
-The
-.BR sendmmsg ()
-system call is an extension of
-.BR sendmsg (2)
-that allows the caller to transmit multiple messages on a socket
-using a single system call.
-(This has performance benefits for some applications.)
-.\" See commit 228e548e602061b08ee8e8966f567c12aa079682
-
-The
-.I sockfd
-argument is the file descriptor of the socket
-on which data is to be transmitted.
-
-The
-.I msgvec
-argument is a pointer to an array of
-.I mmsghdr
-structures.
-The size of this array is specified in
-.IR vlen .
-
-The
-.I mmsghdr
-structure is defined in
-.I <sys/socket.h>
-as:
-
-.in +4n
-.nf
-struct mmsghdr {
- struct msghdr msg_hdr; /* Message header */
- unsigned int msg_len; /* Number of bytes transmitted */
-};
-.fi
-.in
-.PP
-The
-.I msg_hdr
-field is a
-.I msghdr
-structure, as described in
-.BR sendmsg (2).
-The
-.I msg_len
-field is used to return the number of bytes sent from the message in
-.IR msg_hdr
-(i.e., the same as the return value from a single
-.BR sendmsg (2)
-call).
-
-The
-.I flags
-argument contains flags ORed together.
-The flags are the same as for
-.BR sendmsg (2).
-
-A blocking
-.BR sendmmsg ()
-call blocks until
-.I vlen
-messages have been sent.
-A nonblocking call sends as many messages as possible
-(up to the limit specified by
-.IR vlen )
-and returns immediately.
-
-On return from
-.BR sendmmsg (),
-the
-.I msg_len
-fields of successive elements of
-.IR msgvec
-are updated to contain the number of bytes transmitted from the corresponding
-.IR msg_hdr .
-The return value of the call indicates the number of elements of
-.I msgvec
-that have been updated.
-.SH RETURN VALUE
-On success,
-.BR sendmmsg ()
-returns the number of messages sent from
-.IR msgvec ;
-if this is less than
-.IR vlen ,
-the caller can retry with a further
-.BR sendmmsg ()
-call to send the remaining messages.
-
-On error, \-1 is returned, and
-.I errno
-is set to indicate the error.
-.SH ERRORS
-Errors are as for
-.BR sendmsg (2).
-An error is returned only if no datagrams could be sent.
-.\" commit 728ffb86f10873aaf4abd26dde691ee40ae731fe
-.\" ... only return an error if no datagrams could be sent.
-.\" If less than the requested number of messages were sent, the application
-.\" must retry starting at the first failed one and if the problem is
-.\" persistent the error will be returned.
-.\"
-.\" This matches the behavior of other syscalls like read/write - it
-.\" is not an error if less than the requested number of elements are sent.
-.SH VERSIONS
-The
-.BR sendmmsg ()
-system call was added in Linux 3.0.
-Support in glibc was added in version 2.14.
-.SH CONFORMING TO
-.BR sendmmsg ()
-is Linux-specific.
-.SH NOTES
-The value specified in
-.I vlen
-is capped to
-.B UIO_MAXIOV
-(1024).
-.\" commit 98382f419f32d2c12d021943b87dea555677144b
-.\" net: Cap number of elements for sendmmsg
-.\"
-.\" To limit the amount of time we can spend in sendmmsg, cap the
-.\" number of elements to UIO_MAXIOV (currently 1024).
-.\"
-.\" For error handling an application using sendmmsg needs to retry at
-.\" the first unsent message, so capping is simpler and requires less
-.\" application logic than returning EINVAL.
-.SH EXAMPLE
-The example below uses
-.BR sendmmsg ()
-to send
-.I onetwo
-and
-.I three
-in two distinct UDP datagrams using one system call.
-The contents of the first datagram originates from a pair of buffers.
-
-.nf
-#define _GNU_SOURCE
-#include <netinet/ip.h>
-#include <stdio.h>
-#include <stdlib.h>
-#include <string.h>
-#include <sys/types.h>
-#include <sys/socket.h>
-
-int
-main(void)
-{
- int sockfd;
- struct sockaddr_in sa;
- struct mmsghdr msg[2];
- struct iovec msg1[2], msg2;
- int retval;
-
- sockfd = socket(AF_INET, SOCK_DGRAM, 0);
- if (sockfd == \-1) {
- perror("socket()");
- exit(EXIT_FAILURE);
- }
-
- sa.sin_family = AF_INET;
- sa.sin_addr.s_addr = htonl(INADDR_LOOPBACK);
- sa.sin_port = htons(1234);
- if (connect(sockfd, (struct sockaddr *) &sa, sizeof(sa)) == \-1) {
- perror("connect()");
- exit(EXIT_FAILURE);
- }
-
- memset(msg1, 0, sizeof(msg1));
- msg1[0].iov_base = "one";
- msg1[0].iov_len = 3;
- msg1[1].iov_base = "two";
- msg1[1].iov_len = 3;
-
- memset(&msg2, 0, sizeof(msg2));
- msg2.iov_base = "three";
- msg2.iov_len = 5;
-
- memset(msg, 0, sizeof(msg));
- msg[0].msg_hdr.msg_iov = msg1;
- msg[0].msg_hdr.msg_iovlen = 2;
-
- msg[1].msg_hdr.msg_iov = &msg2;
- msg[1].msg_hdr.msg_iovlen = 1;
-
- retval = sendmmsg(sockfd, msg, 2, 0);
- if (retval == \-1)
- perror("sendmmsg()");
- else
- printf("%d messages sent\\n", retval);
-
- exit(0);
-}
-.fi
-.SH SEE ALSO
-.BR recvmmsg (2),
-.BR sendmsg (2),
-.BR socket (2),
-.BR socket (7)
-.SH COLOPHON
-This page is part of release 3.79 of the Linux
-.I man-pages
-project.
-A description of the project,
-information about reporting bugs,
-and the latest version of this page,
-can be found at
-\%http://www.kernel.org/doc/man\-pages/.
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