From: Mingming <cmm@us.ibm.com>
Subject: Re: [PATCH 2/2 V3] allow direct IO to fallocate and holes
Date: Thu, 10 Sep 2009 13:17:00 -0700
Message-ID: <1252613820.7006.8.camel@mingming-laptop>
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Cc: "Aneesh Kumar K.V" <aneesh.kumar@linux.vnet.ibm.com>,
	Theodore Tso <tytso@mit.edu>, linux-ext4@vger.kernel.org,
	Eric Sandeen <sandeen@redhat.com>
To: Jan Kara <jack@suse.cz>
In-Reply-To: <20090910085440.GB607@duck.suse.cz>
Sender: linux-ext4-owner@vger.kernel.org

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).
> 
> 									Honza


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?

Mingming