Date: Fri, 8 Aug 1997 00:00:02 -0700 (PDT) From: tetsuya@secom-sis.co.jp (Tetsuya Furukawa) To: freebsd-bugs Subject: Re: kern/4243: file locking doesn't work for pipe Message-ID: <199708080700.AAA27925@hub.freebsd.org>
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The following reply was made to PR kern/4243; it has been noted by GNATS.
From: tetsuya@secom-sis.co.jp (Tetsuya Furukawa)
To: peter@spinner.dialix.com.au
Cc: dg@root.com, FreeBSD-gnats-submit@FreeBSD.ORG
Subject: Re: kern/4243: file locking doesn't work for pipe
Date: Fri, 8 Aug 1997 15:58:26 +0900
Peter Wemm wrote:
>Yeah, it's kinda nonsensical, but useful in certain situations where the
>same fd is shared between processes.
The purpose that Apache's URL rewriting module locks a pipe is
exactly that.
The latest version of the module says:
----
/* The locking support for the RewriteMap programs:
Locking a pipe to the child works fine under most
Unix derivates, but braindead SunOS 4.1.x has
problems with this approach... */
#define USE_PIPE_LOCKING 1
#ifdef SUNOS4
#undef USE_PIPE_LOCKING
#endif
----
<URL:http://www.engelschall.com/sw/mod_rewrite/distrib/mod_rewrite-SNAP/src/mod_rewrite.h>;
I made a simple program to check whether flock() works for a pipe.
----
#include <sys/file.h>
#include <sys/errno.h>
#include <errno.h>
#include <stdio.h>
#include <unistd.h>
int
main()
{
int fds[2];
char c;
pipe(fds);
if (fork() == 0) {
/* child */
flock(fds[1], LOCK_EX);
sleep(2);
exit(0);
}
/* parent */
sleep(1);
if (flock(fds[1], LOCK_EX | LOCK_NB) == -1) {
if (errno == EWOULDBLOCK)
printf("flock works fine.\n");
else
printf("flock fails: %s\n", strerror(errno));
} else
printf("flock is discarded.\n");
return 0;
}
----
Results:
FreeBSD 2.2-STABLE i386 flock fails: Operation not supported
FreeBSD 2.1.7.1-RELEASE i386 flock fails: Operation not supported
Linux 2.0.29 i686 flock is discarded.
Solaris 2.5.1 sparc flock works fine.
Linux is really braindead. :-(
I will send the results to the developer of the Apache's module
and request to use the other locking method.
--
Tetsuya FURUKAWA in Tokyo, Japan
PGP Key fingerprint = C2 86 A6 7C 72 A0 A1 94 F4 4C 83 9D D1 E3 47 BD
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