1SENDMMSG(2) Linux Programmer's Manual SENDMMSG(2)
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6 sendmmsg - send multiple messages on a socket
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9 #define _GNU_SOURCE
10 #include <sys/socket.h>
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12 int sendmmsg(int sockfd, struct mmsghdr *msgvec, unsigned int vlen,
13 unsigned int flags);
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16 The sendmmsg() system call is an extension of sendmsg(2) that allows
17 the caller to transmit multiple messages on a socket using a single
18 system call. (This has performance benefits for some applications.)
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20 The sockfd argument is the file descriptor of the socket on which data
21 is to be transmitted.
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23 The msgvec argument is a pointer to an array of mmsghdr structures.
24 The size of this array is specified in vlen.
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26 The mmsghdr structure is defined in <sys/socket.h> as:
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28 struct mmsghdr {
29 struct msghdr msg_hdr; /* Message header */
30 unsigned int msg_len; /* Number of bytes transmitted */
31 };
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33 The msg_hdr field is a msghdr structure, as described in sendmsg(2).
34 The msg_len field is used to return the number of bytes sent from the
35 message in msg_hdr (i.e., the same as the return value from a single
36 sendmsg(2) call).
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38 The flags argument contains flags ORed together. The flags are the
39 same as for sendmsg(2).
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41 A blocking sendmmsg() call blocks until vlen messages have been sent.
42 A nonblocking call sends as many messages as possible (up to the limit
43 specified by vlen) and returns immediately.
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45 On return from sendmmsg(), the msg_len fields of successive elements of
46 msgvec are updated to contain the number of bytes transmitted from the
47 corresponding msg_hdr. The return value of the call indicates the num‐
48 ber of elements of msgvec that have been updated.
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51 On success, sendmmsg() returns the number of messages sent from msgvec;
52 if this is less than vlen, the caller can retry with a further send‐
53 mmsg() call to send the remaining messages.
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55 On error, -1 is returned, and errno is set to indicate the error.
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58 Errors are as for sendmsg(2). An error is returned only if no data‐
59 grams could be sent.
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62 The sendmmsg() system call was added in Linux 3.0. Support in glibc
63 was added in version 2.14.
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66 sendmmsg() is Linux-specific.
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69 The value specified in vlen is capped to UIO_MAXIOV (1024).
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72 recvmmsg(2), sendmsg(2), socket(2), socket(7)
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76Linux 2011-09-09 SENDMMSG(2)