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Date: Thu, 25 Aug 2005 01:24:40 -0700
From: Andrew Morton <akpm@osdl.org>
To: Jan Blunck <j.blunck@tu-harburg.de>
Cc: torvalds@osdl.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH][RESEND] don't allow sys_readahead() on files opened
 with O_DIRECT
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Jan Blunck <j.blunck@tu-harburg.de> wrote:
>
> IMO sys_readahead() doesn't make sense if the file is opened with
> O_DIRECT, because the page cache is stuffed but never used. Therefore
> this patch changes that by letting the call return with -EINVAL.
> 

a) It doesn't hurt, it's just a bit of a silly thing to do.

b) posix_fadvise(POSIX_FADV_WILLNEED) should get the same treatment (and
   it's the preferred way of doing readahead).

c) O_DIRECT fd's should, as much as possible, offer the same ABI as
   buffered fd's.

d) The patch could break existing apps.