linux-kernel - Re: [PATCH 2/5] revoke: core code

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Message-ID: <20070316145855.5604d7d8@lxorguk.ukuu.org.uk>
Date:	Fri, 16 Mar 2007 14:58:55 +0000
From:	Alan Cox <alan@...rguk.ukuu.org.uk>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Pekka J Enberg <penberg@...helsinki.fi>,
	linux-kernel@...r.kernel.org, hch@...radead.org
Subject: Re: [PATCH 2/5] revoke: core code

> I'm not sure that running do_fsync() will guarantee that all sys_write()
> callers will have finished their syscall.  Probably they will have, in
> practice.  But there is logic in the sync paths to deliberately bale out
> if we're competing with ongoing dirtyings, to avoid livelocking.

For device files you really need to call into the device driver for this
(->flush etc).

> However, modifying i_size like this might be a problem - the inode could be
> dirty and it'll get written to disk!  Perhaps we could change i_size_read()
> to cheat and to return zero if there's a revoke in progress.

The cheating is a bit messier than that - you might be revoking on a
cluster file system and I'm still trying to get my head around what the
semantics for that are. Lying about sizes will break the coherency
protocols I think

Serious question - do we actually need revoke() on a normal file ? BSD
has never had this, SYS5 has never had this.

Alan
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