From mboxrd@z Thu Jan 1 00:00:00 1970 From: Hannes Reinecke Subject: Re: [PATCH 3/7] dm core: enable request-based dm Date: Fri, 24 Apr 2009 10:50:50 +0200 Message-ID: <49F17D6A.3020305@suse.de> References: <49F17409.4060201@ct.jp.nec.com> <49F174CD.403@ct.jp.nec.com> Reply-To: device-mapper development Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable Return-path: In-Reply-To: <49F174CD.403@ct.jp.nec.com> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: dm-devel-bounces@redhat.com Errors-To: dm-devel-bounces@redhat.com To: device-mapper development Cc: Alasdair Kergon List-Id: dm-devel.ids Kiyoshi Ueda wrote: > This patch enables request-based dm. >=20 > o Request-based dm and bio-based dm coexist, since there are > some target drivers which are more fitting to bio-based dm. > Also, there are other bio-based devices in the kernel > (e.g. md, loop). > Since bio-based device can't receive struct request, > there are some limitations on device stacking between > bio-based and request-based. >=20 > type of underlying device > bio-based requeset-based > ---------------------------------------------- > bio-based OK OK > request-based NG OK >=20 > The device type is recognized by the queue flag in the kernel, > so dm follows that. >=20 > o The type of a dm device is decided at the first table binding time. > Once the type of a dm device is decided, the type can't be changed. >=20 > o Mempool allocations are deferred to at the table loading time, since > mempools for request-based dm are different from those for bio-based > dm and needed mempool type is fixed by the type of table. >=20 > o Currently, request-based dm supports only tables that have a single > target. To support multiple targets, we need to support request > splitting or prevent bio/request from spanning multiple targets. > The former needs lots of changes in the block layer, and the latter > needs that all target drivers support merge() function. > Both will take a time. >=20 >=20 > Signed-off-by: Kiyoshi Ueda > Signed-off-by: Jun'ichi Nomura Acked-by: Hannes Reinecke Cheers, Hannes --=20 Dr. Hannes Reinecke zSeries & Storage hare@suse.de +49 911 74053 688 SUSE LINUX Products GmbH, Maxfeldstr. 5, 90409 N=C3=BCrnberg GF: Markus Rex, HRB 16746 (AG N=C3=BCrnberg)