from small one page howto to huge articles all in one place
 

search text in:





Poll
Which filesystem do you use?






poll results

Last additions:
using iotop to find disk usage hogs

using iotop to find disk usage hogs

words:

887

views:

185937

userrating:

average rating: 1.7 (102 votes) (1=very good 6=terrible)


May 25th. 2007:
Words

486

Views

250337

why adblockers are bad


Workaround and fixes for the current Core Dump Handling vulnerability affected kernels

Workaround and fixes for the current Core Dump Handling vulnerability affected kernels

words:

161

views:

137481

userrating:

average rating: 1.4 (42 votes) (1=very good 6=terrible)


April, 26th. 2006:

Druckversion
You are here: manpages





SENDMMSG

Section: Linux Programmer's Manual (2)
Updated: 2017-09-15
Index Return to Main Contents
 

NAME

sendmmsg - send multiple messages on a socket  

SYNOPSIS

#define _GNU_SOURCE         /* See feature_test_macros(7) */
#include <sys/socket.h>

int sendmmsg(int sockfd, struct mmsghdr *msgvec, unsigned int vlen,
             unsigned int flags);
 

DESCRIPTION

The sendmmsg() system call is an extension of 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.)

The sockfd argument is the file descriptor of the socket on which data is to be transmitted.

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 bytes transmitted */ };

The msg_hdr field is a msghdr structure, as described in sendmsg(2). The msg_len field is used to return the number of bytes sent from the message in msg_hdr (i.e., the same as the return value from a single sendmsg(2) call).

The flags argument contains flags ORed together. The flags are the same as for sendmsg(2).

A blocking sendmmsg() call blocks until vlen messages have been sent. A nonblocking call sends as many messages as possible (up to the limit specified by vlen) and returns immediately.

On return from sendmmsg(), the msg_len fields of successive elements of msgvec are updated to contain the number of bytes transmitted from the corresponding msg_hdr. The return value of the call indicates the number of elements of msgvec that have been updated.  

RETURN VALUE

On success, sendmmsg() returns the number of messages sent from msgvec; if this is less than vlen, the caller can retry with a further sendmmsg() call to send the remaining messages.

On error, -1 is returned, and errno is set to indicate the error.  

ERRORS

Errors are as for sendmsg(2). An error is returned only if no datagrams could be sent.  

VERSIONS

The sendmmsg() system call was added in Linux 3.0. Support in glibc was added in version 2.14.  

CONFORMING TO

sendmmsg() is Linux-specific.  

NOTES

The value specified in vlen is capped to UIO_MAXIOV (1024).  

EXAMPLE

The example below uses sendmmsg() to send onetwo and three in two distinct UDP datagrams using one system call. The contents of the first datagram originates from a pair of buffers.

#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 addr;
    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);
    }


    addr.sin_family = AF_INET;
    addr.sin_addr.s_addr = htonl(INADDR_LOOPBACK);
    addr.sin_port = htons(1234);
    if (connect(sockfd, (struct sockaddr *) &addr, sizeof(addr)) == -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); }  

SEE ALSO

recvmmsg(2), sendmsg(2), socket(2), socket(7)  

COLOPHON

This page is part of release 4.13 of the Linux man-pages project. A description of the project, information about reporting bugs, and the latest version of this page, can be found at https://www.kernel.org/doc/man-pages/.


 

Index

NAME
SYNOPSIS
DESCRIPTION
RETURN VALUE
ERRORS
VERSIONS
CONFORMING TO
NOTES
EXAMPLE
SEE ALSO
COLOPHON





Support us on Content Nation
rdf newsfeed | rss newsfeed | Atom newsfeed
- Powered by LeopardCMS - Running on Gentoo -
Copyright 2004-2020 Sascha Nitsch Unternehmensberatung GmbH
Valid XHTML1.1 : Valid CSS : buttonmaker
- Level Triple-A Conformance to Web Content Accessibility Guidelines 1.0 -
- Copyright and legal notices -
Time to create this page: 12.8 ms