linux-kernel - Re: Approaches to making io

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Date:	Thu, 1 Sep 2011 09:15:31 -0700
From:	Jeremy Allison <jra@...ba.org>
To:	Christoph Hellwig <hch@...radead.org>
Cc:	Jeremy Allison <jra@...ba.org>,
	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 12:04:36PM -0400, Christoph Hellwig wrote:
> 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.

That would help us enormously - it'd be Linux only of course but
we could easily add support for that.

Can you propose the design here so we can run it past some of the
Solaris/FreeBSD folks (it'd be nice if we could get broader adoption) ?

Jeremy.
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