linux-ext4 - Re: [PATCH 2/2 V3] allow direct IO to fallocate and holes

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Date:	Mon, 14 Sep 2009 13:25:44 +0200
From:	Jan Kara <jack@...e.cz>
To:	Mingming <cmm@...ibm.com>
Cc:	Jan Kara <jack@...e.cz>,
	"Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>,
	Theodore Tso <tytso@....edu>, linux-ext4@...r.kernel.org,
	Eric Sandeen <sandeen@...hat.com>
Subject: Re: [PATCH 2/2 V3] allow direct IO to fallocate and holes

On Thu 10-09-09 13:17:00, Mingming wrote:
> On Thu, 2009-09-10 at 10:54 +0200, Jan Kara wrote:
> > On Thu 10-09-09 13:27:30, Aneesh Kumar K.V wrote:
> > > On Wed, Sep 09, 2009 at 01:51:02PM -0700, Mingming wrote:
> > > .....
> > > .....
> > > 
> > > > >   I think fsync() still won't work correctly since it can happen user sees
> > > > > AIO completed, calls fsync() that completes, 
> > > > 
> > > > hmm, does fsync() ensure user sees AIO data completed?
> > > >
> > > 
> > > If we call fsync after getting AIO completion event and crash we should
> > > ensure that the data can be read back properly. That is either
> > > 
> > > a) we should ensure that we convert the extent before returning the io
> > >     completion event
> > > b) Or the fsync should be able to guarantee that it will force the extent
> > >    conversion pending on the file.
> >   Exactly.
> > 
> > a) should happen in the sync-io case where we can afford to do IO from the
> > end_io callback (and due to flush_workqueue call, it happens with the
> > current Mingming's patch so that is file). But for tha aio case, we have to
> > somehow implement b).
> > 
> to implement b), I think we need to keep track of a list of completed
> IOs from AIO, but not get converted extents, and force fsync to run
> flush_queue on those completed IOs?
  Yes that would work fine.

									Honza
-- 
Jan Kara <jack@...e.cz>
SUSE Labs, CR
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