linux-kernel - Re: Approaches to making io

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Date:	Thu, 1 Sep 2011 12:04:36 -0400
From:	Christoph Hellwig <hch@...radead.org>
To:	Jeremy Allison <jra@...ba.org>
Cc:	Ulrich Drepper <drepper@...adia.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Daniel Ehrenberg <dehrenberg@...gle.com>,
	Jens Axboe <axboe@...nel.dk>, Jeff Moyer <jmoyer@...hat.com>,
	linux-kernel@...r.kernel.org, linux-aio@...ck.org
Subject: Re: Approaches to making io_submit not block

On Thu, Sep 01, 2011 at 08:58:45AM -0700, Jeremy Allison wrote:
> Yes I did consider that of course. Problem is that leads you to the
> nightmare that is losing all fcntl locks on the file when any of the
> descriptors are closed. Of course we already have internal work arounds
> for that - but they're not scalable in this case.  We'd have to dup on
> every read/write, and because of the fcntl lock problem we have to keep
> all fd's around until the final close of the file. Don't tell us to
> implement our own locking instead because (a) we already do in the case
> where we don't need locking consistency with NFS and (b) most vendors insist on
> locking consistency with NFS - not good if locks on one protocol aren't
> seen by another.

We could easily give you an fcntl / dup3 flag to only release posix
locks on the final close of a struct file if that helps you.
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