From: Andrew Morton <akpm@osdl.org>
To: Werner Almesberger <wa@almesberger.net>
Cc: linux-kernel@vger.kernel.org
Subject: Re: VFS locking: f_pos thread-safe ?
Date: Thu, 5 Feb 2004 23:55:17 -0800 [thread overview]
Message-ID: <20040205235517.2bb4c073.akpm@osdl.org> (raw)
In-Reply-To: <20040206041223.A18820@almesberger.net>
Werner Almesberger <wa@almesberger.net> wrote:
>
> "[...] read( ) [...] shall be atomic with respect to each other
> in the effects specified in IEEE Std. 1003.1-200x when they
> operate on regular files. If two threads each call one of these
> functions, each call shall either see all of the specified
> effects of the other call, or none of them."
Whichever thread finishes its read last gets to update f_pos.
I'm struggling a bit to understand what they're calling for there. If
thread A enters a read and then shortly afterwards thread B enters the
read, does thread B see an f_pos which starts out at the beginning of A's
read, or the end of it?
Similar questions apply as the threads exit their read()s.
Either way, there's no way in which we should serialise concurrent readers.
That would really suck for sensible apps which are using pread64().
next prev parent reply other threads:[~2004-02-06 7:53 UTC|newest]
Thread overview: 24+ messages / expand[flat|nested] mbox.gz Atom feed top
2004-02-06 7:12 VFS locking: f_pos thread-safe ? Werner Almesberger
2004-02-06 7:55 ` Andrew Morton [this message]
2004-02-06 18:37 ` Joel Becker
2004-02-06 19:05 ` Matthias Urlichs
2004-02-07 1:35 ` Joel Becker
2004-02-06 20:09 ` Werner Almesberger
2004-02-06 20:56 ` Valdis.Kletnieks
2004-02-07 0:55 ` Werner Almesberger
2004-02-06 20:54 ` Andries Brouwer
2004-02-07 23:45 ` Werner Almesberger
-- strict thread matches above, loose matches on Subject: below --
2004-02-06 9:09 Matt
2004-02-06 9:16 ` Andrew Morton
2004-02-06 9:26 ` Matt
2004-02-06 9:35 ` Andrew Morton
2004-02-06 10:19 ` Matthias Urlichs
2004-02-06 11:18 ` viro
2004-02-06 18:59 ` Matthias Urlichs
2004-02-06 19:54 ` Werner Almesberger
2004-02-08 15:58 ` Kai Henningsen
2004-02-19 15:14 ` Pavel Machek
[not found] ` <20040206101941.4cd9c882.shemminger@osdl.org>
2004-02-06 18:47 ` Matthias Urlichs
2004-02-06 13:50 ` Werner Almesberger
2004-02-06 13:56 ` viro
2004-02-06 14:24 ` Werner Almesberger
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