[PATCH] sendmmsg.2: Updated fixme, added example

[Elie De Brauwer <eliedebrauwer-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>]

Hello all,

Updated my patch with the comment from Michael (thanks for the feedback btw).
I however did not include the shell session using netcat for the simple
reason that the output of netcat does not illustrate that the call functions
correctly. The output of netcat would be the same no matter how much 
UDP datagrams were created in the transmission, the only reason why I showed
it in my previous e-mail was to avoid the generation of icmp port
unreachable which would break my tcpdump capture. This latter one is what I
really wanted to show, but i think that one's a bit too far fetched to be 
held in a manpage.

gr
E. 

---
 man2/sendmmsg.2 |   70 +++++++++++++++++++++++++++++++++++++++++++++++++++++--
 1 file changed, 68 insertions(+), 2 deletions(-)

diff --git a/man2/sendmmsg.2 b/man2/sendmmsg.2
index 12ad3ff..b426b4d 100644
--- a/man2/sendmmsg.2
+++ b/man2/sendmmsg.2
@@ -23,8 +23,6 @@
 .\" Formatted or processed versions of this manual, if unaccompanied by
 .\" the source, must acknowledge the copyright and authors of this work.
 .\"
-.\" FIXME Adding an example program would improve this page
-.\"
 .TH SENDMMSG 2 2012-02-27 "Linux" "Linux Programmer's Manual"
 .SH NAME
 sendmmsg \- send multiple messages on a socket
@@ -165,6 +163,74 @@ is capped to
 .\"     For error handling an application using sendmmsg needs to retry at
 .\"     the first unsent message, so capping is simpler and requires less
 .\"     application logic than returning EINVAL.
+.SH EXAMPLE
+The example below uses 
+.BR sendmmsg ()
+to send  
+.I onetwo
+and 
+.I three
+in two distinct UDP datagrams using one system call. The contents
+of the first datagram originates from a pair of buffers.
+
+.nf
+#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()
+{
+    int sockfd;
+    struct sockaddr_in sa;
+    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);
+    }
+
+    sa.sin_family = AF_INET;             
+    sa.sin_addr.s_addr = htonl(INADDR_LOOPBACK);  
+    sa.sin_port = htons(1234);  
+    if (connect(sockfd, (struct sockaddr *) &sa, sizeof(sa))) {
+        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);
+}
+.fi
 .SH SEE ALSO
 .BR recvmmsg (2),
 .BR sendmsg (2),
-- 
1.7.10.4

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