recvmmsg(2)

1RECVMMSG(2)                Linux Programmer's Manual               RECVMMSG(2)
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NAME

6       recvmmsg - receive multiple messages on a socket
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SYNOPSIS

9       #define _GNU_SOURCE
10       #include <sys/socket.h>
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12       int recvmmsg(int sockfd, struct mmsghdr *msgvec, unsigned int vlen,
13                    unsigned int flags, struct timespec *timeout);
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DESCRIPTION

16       The  recvmmsg()  system  call is an extension of recvmsg(2) that allows
17       the caller to receive multiple messages from a socket  using  a  single
18       system call.  (This has performance benefits for some applications.)  A
19       further extension over recvmsg(2) is  support  for  a  timeout  on  the
20       receive operation.
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22       The  sockfd  argument  is  the file descriptor of the socket to receive
23       data from.
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25       The msgvec argument is a pointer to an  array  of  mmsghdr  structures.
26       The size of this array is specified in vlen.
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28       The mmsghdr structure is defined in <sys/socket.h> as:
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30           struct mmsghdr {
31              struct msghdr msg_hdr;  /* Message header */
32              unsigned int  msg_len;  /* Number of received bytes for header */
33           };
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35       The  msg_hdr  field  is a msghdr structure, as described in recvmsg(2).
36       The msg_len field is the number of bytes returned for  the  message  in
37       the entry.  This field has the same value as the return value of a sin‐
38       gle recvmsg(2) on the header.
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40       The flags argument contains flags ORed together.   The  flags  are  the
41       same as documented for recvmsg(2), with the following addition:
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43       MSG_WAITFORONE
44              Turns on MSG_DONTWAIT after the first message has been received.
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46       The timeout argument points to a struct timespec (see clock_gettime(2))
47       defining a timeout (seconds plus nanoseconds) for  the  receive  opera‐
48       tion.  If timeout is NULL then the operation blocks indefinitely.
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50       A  blocking  recvmmsg()  call  blocks  until  vlen  messages  have been
51       received or until the timeout expires.  A  nonblocking  call  reads  as
52       many  messages as are available (up to the limit specified by vlen) and
53       returns immediately.
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55       On return from recvmmsg(), successive elements of msgvec are updated to
56       contain  information  about each received message: msg_len contains the
57       size of the received message; the subfields of msg_hdr are  updated  as
58       described  in  recvmsg(2).   The return value of the call indicates the
59       number of elements of msgvec that have been updated.
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RETURN VALUE

62       On success, recvmmsg() returns  the  number  of  messages  received  in
63       msgvec;  on  error,  -1  is  returned, and errno is set to indicate the
64       error.
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ERRORS

67       Errors are as for recvmsg(2).  In addition,  the  following  error  can
68       occur:
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70       EINVAL timeout is invalid.
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VERSIONS

73       The recvmmsg() system call was added in Linux 2.6.32.  Support in glibc
74       was added in version 2.12.
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CONFORMING TO

77       recvmmsg() is Linux-specific.
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