linux-kernel - Re: adding proper O_SYNC/O_DSYNC, was Re: O

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Message-ID: <4A9806D9.5050409@redhat.com>
Date:	Fri, 28 Aug 2009 09:33:29 -0700
From:	Ulrich Drepper <drepper@...hat.com>
To:	Christoph Hellwig <hch@...radead.org>
CC:	Jamie Lokier <jamie@...reable.org>, linux-fsdevel@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: adding proper O_SYNC/O_DSYNC, was Re: O_DIRECT and barriers

On 08/28/2009 09:17 AM, Christoph Hellwig wrote:
> I'll put it on my todo list.

Any ABI change like this takes a long time to trickle down.

If this is agreed to be the correct approach then adding the O_* 
definitions earlier is better.  Even if it isn't yet implemented.  Then, 
once the kernel side is implemented, programs are ready to use it.  I 
cannot jump the gun and define the flags myself first.

>   - O_RSYNC basically means we need to commit atime updates before a
>     read returns, right?

No, that's not it.

O_RSYNC on its own just means the data is successfully transferred to 
the calling process (always the case).

O_RSYNC|O_DSYNC means that if a read request hits data that is currently 
in a cache and not yet on the medium, then the write to medium is 
successful before the read succeeds.

O_RSYNC|O_SYNC means the same plus the integrity of file meta 
information (access time etc).

-- 
➧ Ulrich Drepper ➧ Red Hat, Inc. ➧ 444 Castro St ➧ Mountain View, CA ❖
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