linux-kernel - Re: file offset corruption on 32-bit machines?

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Message-ID:  <mj+md-20080410.140857.3331.nikam@ucw.cz>
Date:	Thu, 10 Apr 2008 16:11:24 +0200
From:	Martin Mares <mj@....cz>
To:	Michal Hocko <mhocko@...e.cz>
Cc:	Meelis Roos <mroos@...ux.ee>,
	Linux Kernel list <linux-kernel@...r.kernel.org>,
	linux-fsdevel@...r.kernel.org
Subject: Re: file offset corruption on 32-bit machines?

Hello!

> [*] file_pos_{read,write} (fs/read_write.c) are not called under lock (in 
> sys_read, sys_write, ...), so even if f_pos is written atomically, you will 
> be able to get races when accessing shared descriptor from different threads.

There are however cases when such behavior is perfectly valid: For example
you can have a file of records of a fixed size, whose order does not matter.
Then multiple processes can produce the records in parallel, sharing
a single fd.

> I think that POSIX states, that behavior is undefined under these conditions.

Do you have a pointer to that?

				Have a nice fortnight
-- 
Martin `MJ' Mares                          <mj@....cz>   http://mj.ucw.cz/
Faculty of Math and Physics, Charles University, Prague, Czech Rep., Earth
Mr. Worf, scan that ship."  "Aye, Captain... 600 DPI?
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