From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from [140.186.70.92] (port=40345 helo=eggs.gnu.org) by lists.gnu.org with esmtp (Exim 4.43) id 1P8vCA-0004Lv-Cj for qemu-devel@nongnu.org; Thu, 21 Oct 2010 09:28:39 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1P8vBG-0006Oy-6Z for qemu-devel@nongnu.org; Thu, 21 Oct 2010 09:27:43 -0400 Received: from mx1.redhat.com ([209.132.183.28]:51880) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1P8vBF-0006Oj-T1 for qemu-devel@nongnu.org; Thu, 21 Oct 2010 09:27:42 -0400 Date: Thu, 21 Oct 2010 14:27:38 +0100 From: "Daniel P. Berrange" Subject: Re: [Qemu-devel] [PATCH 2/2] v2 Fix Block Hotplug race with drive_unplug() Message-ID: <20101021132738.GM27578@redhat.com> References: <1287498749-10400-1-git-send-email-ryanh@us.ibm.com> <1287498749-10400-3-git-send-email-ryanh@us.ibm.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1287498749-10400-3-git-send-email-ryanh@us.ibm.com> Reply-To: "Daniel P. Berrange" List-Id: qemu-devel.nongnu.org List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Ryan Harper Cc: Stefan Hajnoczi , Anthony Liguori , qemu-devel@nongnu.org, Kevin Wolf On Tue, Oct 19, 2010 at 09:32:29AM -0500, Ryan Harper wrote: > Block hot unplug is racy since the guest is required to acknowlege the ACPI > unplug event; this may not happen synchronously with the device removal command > > This series aims to close a gap where by mgmt applications that assume the > block resource has been removed without confirming that the guest has > acknowledged the removal may re-assign the underlying device to a second guest > leading to data leakage. > > This series introduces a new montor command to decouple asynchornous device > removal from restricting guest access to a block device. We do this by creating > a new monitor command drive_unplug which maps to a bdrv_unplug() command which > does a qemu_aio_flush; bdrv_flush() and bdrv_close(). Once complete, subsequent > IO is rejected from the device and the guest will get IO errors but continue to > function. > > A subsequent device removal command can be issued to remove the device, to which > the guest may or maynot respond, but as long as the unplugged bit is set, no IO > will be sumbitted. The name 'drive_unplug' suggests to me that the drive object is not being deleted/free()d ? Is that correct understanding, and if so, what is responsible for finally free()ing the drive backend ? Regards, Daniel -- |: Red Hat, Engineering, London -o- http://people.redhat.com/berrange/ :| |: http://libvirt.org -o- http://virt-manager.org -o- http://deltacloud.org :| |: http://autobuild.org -o- http://search.cpan.org/~danberr/ :| |: GnuPG: 7D3B9505 -o- F3C9 553F A1DA 4AC2 5648 23C1 B3DF F742 7D3B 9505 :|