From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:35278) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1dIzyD-0006IJ-1b for qemu-devel@nongnu.org; Thu, 08 Jun 2017 12:07:38 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1dIzyA-0001Mw-E5 for qemu-devel@nongnu.org; Thu, 08 Jun 2017 12:07:37 -0400 From: Juan Quintela In-Reply-To: <20170608144106.GG25805@umbus.fritz.box> (David Gibson's message of "Fri, 9 Jun 2017 00:41:06 +1000") References: <20170608144106.GG25805@umbus.fritz.box> Reply-To: quintela@redhat.com Date: Thu, 08 Jun 2017 18:07:31 +0200 Message-ID: <87o9tya2f0.fsf@secure.mitica> MIME-Version: 1.0 Content-Type: text/plain Subject: Re: [Qemu-devel] unplug_request and migration List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: David Gibson Cc: dgilbert@redhat.com, qemu-ppc@nongnu.org, qemu-devel@nongnu.org David Gibson wrote: > Hi Dave & Juan, > > I'm hoping one of you can answer this. > > I'm currently grappling with (amongst other things) a pseries machine > racing a hot unplug operation with a migrate. There's various issues > with what interim state we need, and which bits of it need to be > migrated that I'm still investigating. But, there's a more general > question that I'm guessing must have already been addressed for x86. > > For any "soft" unplug device - i.e. using ->unplug_request, rather > than ->unplug, giving a device_del command will just ask the guest > nicely to release the device, with the completion of the unplug > happening only if and when the guest indicates it's ready for the > device to go away. AFAICT, the device_del command will return as soon > as the request is made, but if the guest is busy, the completion of > the hot unplug could take arbitrarily long. > > So, what happens if there's a migration in between the unplug_request > and the guest completing the unplug? How does libvirt (or whatever) > know whether to include the device on the destination machine command > line? On upstream, I removed the posibility of doing a hotplug/unplug while we are migrating. But if device del has returned, I can't see how that can be detected. Later, Juan.