From mboxrd@z Thu Jan 1 00:00:00 1970 From: George Dunlap Subject: Re: [Qemu-devel] [PATCH v2] xen_disk: support "direct-io-safe" backend option Date: Fri, 28 Jun 2013 17:51:13 +0100 Message-ID: <51CDBF01.6060903@eu.citrix.com> References: Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii"; Format="flowed" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Sender: xen-devel-bounces@lists.xen.org Errors-To: xen-devel-bounces@lists.xen.org To: Stefano Stabellini Cc: xen-devel@lists.xensource.com, Ian Jackson List-Id: xen-devel@lists.xenproject.org On 28/06/13 17:16, Stefano Stabellini wrote: > On Thu, 27 Jun 2013, Stefano Stabellini wrote: >> Support backend option "direct-io-safe". This is documented as >> follows in the Xen backend specification: >> >> * direct-io-safe >> * Values: 0/1 (boolean) >> * Default Value: 0 >> * >> * The underlying storage is not affected by the direct IO memory >> * lifetime bug. See: >> * http://lists.xen.org/archives/html/xen-devel/2012-12/msg01154.html >> * >> * Therefore this option gives the backend permission to use >> * O_DIRECT, notwithstanding that bug. >> * >> * That is, if this option is enabled, use of O_DIRECT is safe, >> * in circumstances where we would normally have avoided it as a >> * workaround for that bug. This option is not relevant for all >> * backends, and even not necessarily supported for those for >> * which it is relevant. A backend which knows that it is not >> * affected by the bug can ignore this option. >> * >> * This option doesn't require a backend to use O_DIRECT, so it >> * should not be used to try to control the caching behaviour. >> >> Also, BDRV_O_NATIVE_AIO is ignored if BDRV_O_NOCACHE, so clarify the >> default flags passed to the qemu block layer. >> >> The original proposal for a "cache" backend option has been dropped >> because it was believed too wide, especially considering that at the >> moment the backend doesn't have a way to tell the toolstack that it is >> capable of supporting it. >> >> Signed-off-by: Stefano Stabellini >> Signed-off-by: Ian Jackson > George, should I go ahead and commit to the qemu-xen tree? Yes, I think it's pretty important to have the override in there: Acked-by: George Dunlap