netdev - Question on UNIX domain socket.

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Message-Id: <201010262115.FEH09326.OMFJHSVOFLQFOt@I-love.SAKURA.ne.jp>
Date:	Tue, 26 Oct 2010 21:15:25 +0900
From:	Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
To:	mtk.manpages@...il.com
Cc:	netdev@...r.kernel.org
Subject: Question on UNIX domain socket.

Hello.

Is the latest manpage for UNIX domain socket is at
http://www.kernel.org/doc/man-pages/online/pages/man7/unix.7.html ?

I got a question. Above page says

   pathname: a UNIX domain socket can be bound to a null-terminated file
   system pathname using bind(2).  When the address of the socket is returned
   by getsockname(2), getpeername(2), and accept(2), its length is
   offsetof(struct sockaddr_un, sun_path) + strlen(sun_path) + 1, and sun_path
   contains the null-terminated pathname.

However, running below program results in
"sun_path *not* containing the null-terminated pathname" (and therefore it is
not safe to use printf("%s", sun_path) even if sun_path[0] != '\0').

Should "sun_path contains the null-terminated pathname" be corrected?

Regards.

----- Test program start -----
#include <stdio.h>
#include <sys/socket.h>
#include <sys/un.h>
#include <unistd.h>

int main(int argc, char *argv[])
{
	union {
		struct sockaddr_un addr;
		char buf[512];
	} u;
	socklen_t len = sizeof(u.addr);
	int fd = socket(PF_UNIX, SOCK_STREAM, 0);
	u.addr.sun_family = AF_UNIX;
	snprintf(u.addr.sun_path, sizeof(u.buf) - 2, "/"
		 "1234567890123456789012345678901234567890"
		 "1234567890123456789012345678901234567890"
		 "1234567890123456789012345678901234567890"
		 "1234567890123456789012345678901234567890");
	if (bind(fd, (struct sockaddr *) &u.addr, sizeof(u.addr)) == EOF)
		return 1;
	memset(&u, 0, sizeof(u)); /* You may comment out this line. */
	printf("len=%d\n", len);
	if (getsockname(fd, (struct sockaddr *) &u.addr, &len) == EOF)
		return 1;
	printf("strlen=%d len=%d\n", strlen(u.addr.sun_path), len);
	return 0;
}
----- Test program end -----

----- Output of test program -----
len=110
strlen=108 len=111
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