linux-kernel - Re: [RFD] BIO_RW_BARRIER - what it means for devices, filesystems, and dm/md.

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Message-ID: <20070601075336.GX86004887@sgi.com>
Date:	Fri, 1 Jun 2007 17:53:36 +1000
From:	David Chinner <dgc@....com>
To:	Neil Brown <neilb@...e.de>
Cc:	David Chinner <dgc@....com>, Phillip Susi <psusi@....rr.com>,
	Jens Axboe <jens.axboe@...cle.com>, david@...g.hm,
	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
	dm-devel@...hat.com, linux-raid@...r.kernel.org,
	Stefan Bader <Stefan.Bader@...ibm.com>,
	Andreas Dilger <adilger@...sterfs.com>,
	Tejun Heo <htejun@...il.com>
Subject: Re: [RFD] BIO_RW_BARRIER - what it means for devices, filesystems, and dm/md.

On Fri, Jun 01, 2007 at 03:59:51PM +1000, Neil Brown wrote:
> On Friday June 1, dgc@....com wrote:
> > On Thu, May 31, 2007 at 02:31:21PM -0400, Phillip Susi wrote:
> > > David Chinner wrote:
> > > >That sounds like a good idea - we can leave the existing
> > > >WRITE_BARRIER behaviour unchanged and introduce a new WRITE_ORDERED
> > > >behaviour that only guarantees ordering. The filesystem can then
> > > >choose which to use where appropriate....
> > > 
> > > So what if you want a synchronous write, but DON'T care about the order? 
> > 
> > submit_bio(WRITE_SYNC, bio);
> > 
> > Already there, already used by XFS, JFS and direct I/O.
> 
> Are you sure?
> 
> You seem to be saying that WRITE_SYNC causes the write to be safe on
> media before the request returns.

Sorry, I wasn't really all that clear :/

What I'm saying the *interface* for higher layer to tell the block layers
that a sync write is being executed is already there. i.e. we can already
tell the block layer that we are doing a synchronous I/O.

Cheers,

Dave.
-- 
Dave Chinner
Principal Engineer
SGI Australian Software Group
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