Hi all,
Please find below a patch with the comments in below (including two
other typo's I seem to have missed yesterday).
Thanks for the comments.
E.
---
man2/recvmmsg.2 | 94 +++++++++++++++++++++++++++++++++++++++++++++++++++++--
1 file changed, 92 insertions(+), 2 deletions(-)
diff --git a/man2/recvmmsg.2 b/man2/recvmmsg.2
index a7b00d4..0c6db49 100644
--- a/man2/recvmmsg.2
+++ b/man2/recvmmsg.2
@@ -21,8 +21,6 @@
.\" Formatted or processed versions of this manual, if unaccompanied by
.\" the source, must acknowledge the copyright and authors of this work.
.\"
-.\" FIXME: This page could be improved with an example program.
-.\"
.TH RECVMMSG 2 2012-05-02 "Linux" "Linux Programmer's Manual"
.SH NAME
recvmmsg \- receive multiple messages on a socket
@@ -165,6 +163,98 @@ Support in glibc was added in version 2.12.
.SH CONFORMING TO
.BR recvmmsg ()
is Linux-specific.
+.SH EXAMPLE
+.PP
+The following program uses
+.BR recvmmsg ()
+to receive multiple messages on a socket and stores
+them in multiple buffers.
+The call returns if all buffers are filled or if the
+timeout specified is expired.
+
+The following snippet periodically generates UDP datagrams
+containing a random number:
+.in +4n
+.nf
+.RB "$" " while true; do echo $RANDOM > /dev/udp/127.0.0.1/1234; sleep 0.25; done"
+.fi
+.in
+
+These datagrams are read by the example application which
+can give the following output:
+.in +4n
+.nf
+.RB "$" " ./a.out"
+5 messages received
+1 11782
+2 11345
+3 304
+4 13514
+5 28421
+.fi
+.in
+.SS Program source
+\&
+.nf
+#define _GNU_SOURCE
+#include <netinet/ip.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <sys/socket.h>
+
+int
+main()
+{
+#define VLEN 10
+#define BUFSIZE 200
+#define TIMEOUT 1
+ int sockfd, retval, i;
+ struct sockaddr_in sa;
+ struct mmsghdr msgs[VLEN];
+ struct iovec iovecs[VLEN];
+ char bufs[VLEN][BUFSIZE+1];
+ struct timespec timeout;
+
+ 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 (bind(sockfd, (struct sockaddr *) &sa, sizeof(sa)) == \-1) {
+ perror("bind()");
+ exit(EXIT_FAILURE);
+ }
+
+ memset(msgs, 0, sizeof(msgs));
+ for (i = 0; i < VLEN; i++) {
+ iovecs[i].iov_base = bufs[i];
+ iovecs[i].iov_len = BUFSIZE;
+ msgs[i].msg_hdr.msg_iov = &iovecs[i];
+ msgs[i].msg_hdr.msg_iovlen = 1;
+ }
+
+ timeout.tv_sec = TIMEOUT;
+ timeout.tv_nsec = 0;
+
+ retval = recvmmsg(sockfd, msgs, VLEN, 0, &timeout);
+ if (retval == \-1) {
+ perror("recvmmsg()");
+ exit(EXIT_FAILURE);
+ }
+
+ printf("%d messages received\\n", retval);
+ for (i = 0; i < retval; i++) {
+ bufs[i][msgs[i].msg_len] = 0;
+ printf("%d %s", i+1, bufs[i]);
+ }
+ exit(EXIT_SUCCESS);
+}
+.fi
.SH SEE ALSO
.BR clock_gettime (2),
.BR recvmsg (2),
--
1.7.10.4
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