From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([208.118.235.92]:46899) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1UI20I-0005BT-0S for qemu-devel@nongnu.org; Tue, 19 Mar 2013 15:15:23 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1UI20F-00049M-Nu for qemu-devel@nongnu.org; Tue, 19 Mar 2013 15:15:21 -0400 Received: from mail.avalus.com ([2001:41c8:10:1dd::10]:39288) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1UI20F-00048T-J6 for qemu-devel@nongnu.org; Tue, 19 Mar 2013 15:15:19 -0400 Date: Tue, 19 Mar 2013 19:15:05 +0000 From: Alex Bligh Message-ID: <0E09404F0675BA19C550B743@nimrod.local> In-Reply-To: References: <1363609123-20748-1-git-send-email-alex@alex.org.uk> <51471767.8030604@redhat.com> <7AC8953FE45335FB794B6DFE@Ximines.local> <51471F14.7030209@redhat.com> <6D0F4ACDA3B7FCF1A50F8B52@Ximines.local> <5147298C.8080900@redhat.com> <51473E82.1020806@redhat.com> <861AFE1A9C44444FD8BAEE16@Ximines.local> <5147512E.5050501@eu.citrix.com> <5147562E.1090203@redhat.com> <5148414C.7060303@redhat.com> <51484328.4030301@eu.citrix.com> <5148489C.70808@redhat.com> <51484A2B.10202@eu.citrix.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii; format=flowed Content-Transfer-Encoding: 7bit Content-Disposition: inline Subject: Re: [Qemu-devel] [Xen-devel] [PATCHv3] QEMU(upstream): Disable xen's use of O_DIRECT by default as it results in crashes. Reply-To: Alex Bligh List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: George Dunlap , Paolo Bonzini Cc: Ian Campbell , Stefano Stabellini , Alex Bligh , Ian Jackson , qemu-devel@nongnu.org, xen-devel , Anthony Liguori Stefano, George, > This patch only impacts the PV backend in QEMU, not the IDE interface. > PV frontends and backends always disconnect and reconnect during > save/restore. > So we can be *certain* that bdrv_close at the sender side is called > before the new connection is established at the receiver side. > > Unfortunately the QEMU PV backend opens the disk during initialization, > so before the actual connection is established (blk_init). > > Therefore I think that the current change is not safe, but it is pretty > easy to make it safe. > You just need to move the call to blk_open from blk_init to blk_connect. > Actually you can move most of blk_init to blk_connect, you just need to > keep the 4 xenstore_write_be_int at the end of the function. Stefano: do you want me to come up with a patch to do this? --On 19 March 2013 15:29:36 +0000 George Dunlap wrote: > Alex, the title of the changelog should certainly be more specific, so > people aren't confused. Maybe something like the following? > > "Disable use of O_DIRECT when acting as a Xen PV backend" > > And emphasizing in the changelog that this has no effect on qemu when > acting as a device model for Xen? Sure, I can do that. However, my understanding (possibly incorrect) is that when qemu is acting as a device model for xen (i.e. emulated disks) it doesn't use O_DIRECT anyway. I am aware this is a different problem! -- Alex Bligh