Debian Bug report logs - #291121
manpages-dev: flock(2) second time by same process

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Message #5 received at submit@bugs.debian.org (full text, mbox, reply):

From: Kevin Ryde <user42@zip.com.au>

To: submit@bugs.debian.org

Subject: manpages-dev: flock(2) second time by same process

Date: Wed, 19 Jan 2005 08:35:21 +1100

Package: manpages-dev
Version: 2.01-1
Severity: normal

The flock(2) man page says

       A  process  may  only  hold one type of lock (shared or exclusive) on a
       file.  Subsequent flock() calls on an already locked file will  convert
       an existing lock to the new lock mode.

I read this as meaning the lock is associated with the process, and I
tried converting a lock through a second opened fd per the test
program below but it hung after printing "about to do second flock".

The lock is actually associated with the file table entry is it?  Or
the table entry plus the process?  Perhaps this can be clarified.


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

int
main (void)
{
  int x, y, ret;

  x = open ("foo.tmp", O_RDWR | O_CREAT, 0666);
  if (x == -1) perror ("first open");

  ret = flock (x, LOCK_EX);
  if (ret == -1) perror ("first flock");


  y = open ("foo.tmp", O_RDWR);
  if (y == -1) perror ("first open");

  printf ("about to do second flock\n");
  ret = flock (y, LOCK_SH);
  if (ret == -1) perror ("second flock");

  printf ("done\n");
  return 0;
}


-- System Information:
Debian Release: 3.1
  APT prefers unstable
  APT policy: (500, 'unstable')
Architecture: i386 (i586)
Kernel: Linux 2.6.8-1-386
Locale: LANG=C, LC_CTYPE=C (charmap=ANSI_X3.4-1968)

Versions of packages manpages-dev depends on:
ii  manpages                      2.01-1     Manual pages about using a GNU/Lin

-- no debconf information

Message #10 received at 291121@bugs.debian.org (full text, mbox, reply):

From: "Michael Kerrisk" <mtk-manpages@gmx.net>

To: Martin Schulze <joey@infodrom.org>

Cc: 291121@bugs.debian.org

Subject: Re: #291121 flock(2) second time by same process

Date: Tue, 21 Jun 2005 16:36:28 +0200 (MEST)

I agree -- the manual page could offer a little more help.
I've added new text for man-pages-2.04.  (Please close 
this report.)  New text is:

       If a process uses open(2) (or similar) to obtain more than
       one descriptor for the same file,  these  descriptors  are
       treated  independently by flock().  An attempt to lock the
       file using one of these file descriptors may be denied  by
       a  lock  that  the  calling process has already placed via
       another descriptor.

Kevin Ryde said:

> The lock is actually associated with the file table entry 
> is it?  Or the table entry plus the process?  Perhaps this 
> can be clarified.

Note that the manual page did already say the following 
elsewhere:

       Locks created by flock() are associated with an open  file
       table  entry.   This means that duplicate file descriptors
       (created by, for example, fork(2) or dup(2)) refer to  the
       same lock, and this lock may be modified or released using
       any  of  these  descriptors.   Furthermore,  the  lock  is
       released either by an explicit LOCK_UN operation on any of
       these duplicate descriptors, or when all such  descriptors
       have been closed.

Cheers,

Michael

-- 
Michael Kerrisk
maintainer of Linux man pages Sections 2, 3, 4, 5, and 7 

Want to help with man page maintenance?  Grab the latest
tarball at ftp://ftp.win.tue.nl/pub/linux-local/manpages/
and grep the source files for 'FIXME'.

Please submit non-trivial man page suggestions as 
"diff -u" patches.

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Message #17 received at 291121-done@bugs.debian.org (full text, mbox, reply):

From: Justin Pryzby <justinpryzby@users.sourceforge.net>

To: 317037-done@bugs.debian.org, 315411-done@bugs.debian.org, 209323-done@bugs.debian.org, 330877-done@bugs.debian.org, 321131-done@bugs.debian.org, 299795-done@bugs.debian.org, 295666-done@bugs.debian.org, 326520-done@bugs.debian.org, 306517-done@bugs.debian.org, 291121-done@bugs.debian.org, 323851-done@bugs.debian.org, 323062-done@bugs.debian.org, 101433-done@bugs.debian.org, 113812-done@bugs.debian.org, 219695-done@bugs.debian.org, 294890-done@bugs.debian.org

Cc: Martin Schulze <joey@debian.org>, Michael Kerrisk <mtk-manpages@gmx.net>

Subject: fixed in recent uploads of manpages

Date: Tue, 22 Nov 2005 11:35:39 -0500

Version: 2.09-1

These bugs are all reported fixed by the upstream manpages maintainer,
Michael Kerrisk.  For my own convenience, I'm marking them all as
"fixed by version 2.09-1", even though some of them are fixed by
earlier uploads.  The bug number, correct fixed-in version, and title
are listed below:

 #317037 2.06 Difficult to understand in sscanf RETURN VALUE
 #315411 2.09 New upstream release: 2.09
 #209323 2.09 please include pty(4) manpage
 #330877 2.09 read can return EINVAL when using O_DIRECT and buffer not aligned
 #321131 2.08 exit.3 missing "is"
 #299795 2.07 Some library functions' manpage use wrong hyphen
 #295666 2.03 regex.7.gz: The word boundary regexps are unsupported
 #326520 2.08 'man msgget' typo: one line not displayed
 #306517 2.04 epoll_ctl(2) description differs from implementation
 #291121 2.04 flock(2) second time by same process
 #323851 2.08 getpwnam.3 manpage should clarify the scope of pw_dir
 #323062 2.08 clone(2) CLONE_PARENT_SETTID description incorrect

 #101433 2.04 "man setitimer" give bad informations
 #113812 2.04 libc6-dev: iconv prototype
 #317037 2.06 Difficult to understand in sscanf RETURN VALUE
 #219695 2.04 sysconf(3): describes _SC_2_DEV, which doesn't exist
 #294890 2.03 Typo in wait(2): "watpid"

-- 
Clear skies,
Justin

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