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

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Message-ID: <20090910085440.GB607@duck.suse.cz>
Date:	Thu, 10 Sep 2009 10:54:40 +0200
From:	Jan Kara <jack@...e.cz>
To:	"Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>
Cc:	Mingming <cmm@...ibm.com>, Jan Kara <jack@...e.cz>,
	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 13:27:30, 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
-- 
Jan Kara <jack@...e.cz>
SUSE Labs, CR
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