#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);
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.
On error, -1 is returned, and errno is set to indicate the error.
#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); }