From mboxrd@z Thu Jan  1 00:00:00 1970
From: ebiederm@xmission.com (Eric W. Biederman)
Subject: Re: [RFC][PATCH 8/9] vfs: Implement generic revoked file operations
Date: Sun, 12 Apr 2009 13:04:09 -0700
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	<m1prfj5qxp.fsf@fess.ebiederm.org>
	<20090412185659.GE4394@shareable.org>
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Cc: Andrew Morton <akpm@linux-foundation.org>, linux-kernel@vger.kernel.org,
        linux-pci@vger.kernel.org, linux-mm@kvack.org,
        linux-fsdevel@vger.kernel.org, Al Viro <viro@ZenIV.linux.org.uk>,
        Hugh Dickins <hugh@veritas.com>, Tejun Heo <tj@kernel.org>,
        Alexey Dobriyan <adobriyan@gmail.com>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Alan Cox <alan@lxorguk.ukuu.org.uk>,
        Greg Kroah-Hartman <gregkh@suse.de>
To: Jamie Lokier <jamie@shareable.org>
Return-path: <owner-linux-mm@kvack.org>
In-Reply-To: <20090412185659.GE4394@shareable.org> (Jamie Lokier's message of "Sun\, 12 Apr 2009 19\:56\:59 +0100")
Sender: owner-linux-mm@kvack.org
List-Id: linux-fsdevel.vger.kernel.org

Jamie Lokier <jamie@shareable.org> writes:

>> revoked_file_ops return 0 from reads (aka EOF). Tell poll the file is
>> always ready for I/O and return -EIO from all other operations.
>
> I think read should return -EIO too.  If a program is reading from a
> /proc file (say), and the thing it's reading suddenly disappears, EOF
> gives the false impression that it's read to the end of formatted data
> from that file and it can process the data as if it's complete, which
> is wrong.

Good point EIO is the current read return value for a removed proc file.

For closed pipes, and hung up ttys the read return value is 0, and from
my reading that is what bsd returns after a sys_revoke.

The reason I have f_op settable is because I never expected complete
agreement on the return codes, and because it makes auditing and spotting
this kind of thing easier.

I guess I should make two variations on revoked_file_ops then.  Say
eof_file_ops, eio_file_ops.  Identical except for their treatment of
reads.

Eric

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