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Subject: kern/4243: file locking doesn't work for pipe
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>Number:         4243
>Category:       kern
>Synopsis:       file locking doesn't work for pipe
>Confidential:   no
>Severity:       non-critical
>Priority:       medium
>Responsible:    freebsd-bugs
>State:          open
>Class:          sw-bug
>Submitter-Id:   current-users
>Arrival-Date:   Thu Aug  7 01:30:01 PDT 1997
>Last-Modified:
>Originator:     Tetsuya Furukawa
>Organization:
Secom Information System Co.,Ltd.
>Release:        FreeBSD 2.2-STABLE i386
>Environment:
FreeBSD 2.2-STABLE i386 on July 11, 1997

>Description:
In flock() in /sys/kern/kern_descrip.c, the following statement:

    f (fp->f_type != DTYPE_VNODE)
	    return (EOPNOTSUPP);

rejects the file descriptor if fp->f_type == DTYPE_PIPE.
F_SETLK and F_GETLK of fcntl() have also the similar statements.

"Program rewriting map" (RewriteMap mapname prg:filename) of
the URL rewriting module (mod_rewrite) of the Apache HTTP server
uses file locking for pipe, so FreeBSD users cannot use the fine
feature of "program rewriting map".

>How-To-Repeat:
The following program prints "flock: Operation not supported".

--------
#include <sys/file.h>
#include <stdio.h>
#include <unistd.h>

int
main()
{
    int fds[2];
    char c;

    pipe(fds);
    if (flock(fds[1], LOCK_EX) == -1)
	perror("flock");
    write(fds[1], "a", 1);
    read(fds[0], &c, 1);
    return 0;
}
--------

>Fix:
Maybe, modify the three lines like

    if (fp->f_type != DTYPE_VNODE)

into

    if (fp->f_type != DTYPE_VNODE && fp->f_type != DTYPE_PIPE)

I have not tried it, and I'm not convinced that it is safe and right
for I don't know detail of the kernel.

>Audit-Trail:
>Unformatted: