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From: Kiyoshi Ueda <k-ueda@ct.jp.nec.com>
To: nikanth@gmail.com
Cc: dm-devel@redhat.com, jens.axboe@oracle.com, agk@redhat.com,
	James.Bottomley@hansenpartnership.com, j-nomura@ce.jp.nec.com,
	linux-kernel@vger.kernel.org, linux-scsi@vger.kernel.org,
	knikanth@suse.de, k-ueda@ct.jp.nec.com
Subject: Re: [dm-devel] [PATCH 10/13] dm: add core functions for request-based dm
Date: Tue, 28 Oct 2008 12:00:31 -0400 (EDT)	[thread overview]
Message-ID: <20081028.120031.71084925.k-ueda@ct.jp.nec.com> (raw)
In-Reply-To: <807b3a220810240044v1b9f12e3xc3bd5a429b9d4c5@mail.gmail.com>

Hi Nikanth,

On Fri, 24 Oct 2008 13:14:50 +0530, "Nikanth K" wrote:
> On Fri, Sep 12, 2008 at 8:16 PM, Kiyoshi Ueda wrote:
> <snip>
> 
> > +static int dm_make_request(struct request_queue *q, struct bio *bio)
> > +{
> > +       struct mapped_device *md = (struct mapped_device *)q->queuedata;
> > +
> > +       if (unlikely(bio_barrier(bio))) {
> > +               bio_endio(bio, -EOPNOTSUPP);
> > +               return 0;
> > +       }
> > +
> <snip>
> 
> Why not add barrier support in the beginning itself, so that targets
> can be developed with barriers in mind? At least can we make the target
> to return error, instead of the core?

Currently, there is no barrier support in dm, not only request-based.
Barrier support is a different feature in the next step, I think.

As you noticed in the PATCH#11, current request-based dm has
the limitation that multiple targets are not supported, so it may
look barrier support in request-based dm is easy.
But we may be able to remove the limitation in the future, so
depending on it is not a good idea.

Thanks,
Kiyoshi Ueda

  reply	other threads:[~2008-10-28 16:03 UTC|newest]

Thread overview: 26+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2008-09-12 14:38 [PATCH 00/13] request-based dm-multipath Kiyoshi Ueda
2008-09-12 14:40 ` [PATCH 01/13] block: add request update interface Kiyoshi Ueda
2008-09-12 14:41 ` [PATCH 02/13] block: add request submission interface Kiyoshi Ueda
2008-09-14 13:10   ` Boaz Harrosh
2008-09-16 16:06     ` Kiyoshi Ueda
2008-09-16 17:02       ` Jens Axboe
2008-09-16 18:12         ` Kiyoshi Ueda
2008-09-12 14:42 ` [PATCH 03/13] mm: lld busy status exporting interface Kiyoshi Ueda
2008-09-12 14:43 ` [PATCH 04/13] scsi: exports busy status Kiyoshi Ueda
2008-09-12 14:43 ` [PATCH 05/13] block: add a queue flag for request stacking support Kiyoshi Ueda
2008-09-12 14:44 ` [PATCH 06/13] dm: remove unused DM_WQ_FLUSH_ALL Kiyoshi Ueda
2008-09-12 14:44 ` [PATCH 07/13] dm: tidy local_init Kiyoshi Ueda
2008-09-12 14:45 ` [PATCH 08/13] dm: add kmem_cache for request-based dm Kiyoshi Ueda
2008-09-12 14:45 ` [PATCH 09/13] dm: add target interfaces " Kiyoshi Ueda
2008-09-12 14:46 ` [PATCH 10/13] dm: add core functions " Kiyoshi Ueda
2008-10-24  7:44   ` [dm-devel] " Nikanth K
2008-10-28 16:00     ` Kiyoshi Ueda [this message]
     [not found]     ` <490FB852.3FEE.00C5.1@novell.com>
     [not found]       ` <49102C03020000C50002E257@victor.provo.novell.com>
2008-11-04 15:01         ` Kiyoshi Ueda
2008-09-12 14:46 ` [PATCH 11/13] dm: enable " Kiyoshi Ueda
2008-10-24  7:52   ` [dm-devel] " Nikanth K
2008-10-28 16:02     ` Kiyoshi Ueda
2008-09-12 14:46 ` [PATCH 12/13] dm: reject I/O violating new queue limits Kiyoshi Ueda
2008-09-12 14:47 ` [PATCH 13/13] dm-mpath: convert to request-based Kiyoshi Ueda
2008-10-24  7:55   ` [dm-devel] " Nikanth K
2008-10-28 16:03     ` Kiyoshi Ueda
2008-09-14 13:17 ` [PATCH 00/13] request-based dm-multipath Jens Axboe

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