From mboxrd@z Thu Jan 1 00:00:00 1970 Date: Mon, 3 May 2021 09:07:16 -0400 From: Vivek Goyal Message-ID: <20210503130716.GB81443@redhat.com> References: <714BD741-AE3F-4BC5-8DFB-F5C74A8623B1@netapp.com> <20210323145312.GB483930@redhat.com> <40D27E5F-C65A-4441-BA23-ABA6880DAA71@netapp.com> <423DD084-E08F-4402-AD5A-3583117A6B4E@netapp.com> MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <423DD084-E08F-4402-AD5A-3583117A6B4E@netapp.com> Subject: Re: [Virtio-fs] Live migration support for virtio-fs List-Id: Development discussions about virtio-fs List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: "Ge, Xiongzi" Cc: "virtio-fs@redhat.com" , =?iso-8859-1?Q?Marc-Andr=E9?= Lureau , "qemu-devel@nongnu.org" Hi Xiongzi, Try qemu monitor to hot device add/remove that works. I think libvirt support is yet to be added. One issue I faced was that I had to add a pcie root to move virtiofs device off pcie.0 and then hot add remove functionality works. So I had to add pcie root port by adding following to qemu command line. -device pcie-root-port,id=root1,slot=0 And now you can hot add a device using device_add. (qemu) device_add vhost-user-fs-pci,bus=root1,id=myvirtiofs,chardev=char0,tag=myfs,queue-size=1024 - To hot remove device, issue from qemu monitor. (qemu) device_del ex. device_del myvirtiofs Thanks Vivek On Mon, May 03, 2021 at 12:50:56PM +0000, Ge, Xiongzi wrote: > Thanks, Stefan! > It seems that libvirt does not support device-attach for filesystem type device, like virtiofs. Are there any other ways to do this hot-unplugging? > > Xiongzi > > On 4/8/21, 12:21 PM, "Stefan Hajnoczi" wrote: > > On Wed, Apr 07, 2021 at 06:05:29PM +0000, Ge, Xiongzi wrote: > > Thanks Dr Gilbert, Vivek, Stefan, Greg! > > I put together the discussion into this thread and CC qemu-devel@nongnu.org. > > > > Problem: > > Current Virtio-FS does not support live migration. Even when the virtiofs directory is not mounted on the guest, VM cannot do live migration. Any suggestions/interest If we want to make this work so we can still have the live migration feature for other purpose on that VM? > > > > If we already have a shared file system like Ceph, does this make it different? > > (Marc-André: I CCed you regarding D-Bus VMState, see below.) > > During the last virtio-fs call on Wednesday we discussed how to allow > live migration when the file system is not mounted. This means live > migration of a mounted file system still wouldn't be supported, but at > least it would be possible to migrate when the file system is not > mounted. > > The easiest way to do that is to hot unplug the vhost-user-fs-pci device > so that QEMU can live migrate the VM and then hot plug the > vhost-user-fs-pci device again after migration has completed. This > requires either manually performing the hot plug operations or some > automation to do this around live migration. > > A smoother approach would be for QEMU to allow live migration when the > file system is not mounted. Unfortunately it turns out this is actually > rather involved because virtiofsd runs as a separate process from QEMU > and the live migration interface for vhost-user devices is currently > pretty basic > (https://qemu.readthedocs.io/en/latest/interop/dbus-vmstate.html). There > is currently no way for virtiofsd to communicate with QEMU to allow/deny > live migration depending on whether virtiofsd currently has an active > FUSE session (mount). It might be possible to extend the D-Bus VMState > interface and implement support for "migration blockers" as they are > known in QEMU, but I wonder whether it's not better to just work on > full virtio-fs live migration instead. Either task is complex and I > wouldn't recommend it as a first contribution to virtiofsd or QEMU. > > Can you make use of the hotplug approach to live migration? > > Stefan > From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-3.5 required=3.0 tests=BAYES_00,DKIM_INVALID, DKIM_SIGNED,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS,URIBL_BLOCKED autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 4CDBAC433B4 for ; Mon, 3 May 2021 13:09:54 +0000 (UTC) Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 8E173611AD for ; Mon, 3 May 2021 13:09:53 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 8E173611AD Authentication-Results: mail.kernel.org; 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Mon, 3 May 2021 09:07:16 -0400 (EDT) Date: Mon, 3 May 2021 09:07:16 -0400 From: Vivek Goyal To: "Ge, Xiongzi" Subject: Re: [Virtio-fs] Live migration support for virtio-fs Message-ID: <20210503130716.GB81443@redhat.com> References: <714BD741-AE3F-4BC5-8DFB-F5C74A8623B1@netapp.com> <20210323145312.GB483930@redhat.com> <40D27E5F-C65A-4441-BA23-ABA6880DAA71@netapp.com> <423DD084-E08F-4402-AD5A-3583117A6B4E@netapp.com> MIME-Version: 1.0 In-Reply-To: <423DD084-E08F-4402-AD5A-3583117A6B4E@netapp.com> X-Scanned-By: MIMEDefang 2.84 on 10.5.11.23 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=vgoyal@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit Received-SPF: pass client-ip=170.10.133.124; envelope-from=vgoyal@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -34 X-Spam_score: -3.5 X-Spam_bar: --- X-Spam_report: (-3.5 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.698, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_LOW=-0.7, RCVD_IN_MSPIKE_H4=0.001, RCVD_IN_MSPIKE_WL=0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: "virtio-fs@redhat.com" , =?iso-8859-1?Q?Marc-Andr=E9?= Lureau , "Dr. David Alan Gilbert" , Stefan Hajnoczi , "qemu-devel@nongnu.org" Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" Hi Xiongzi, Try qemu monitor to hot device add/remove that works. I think libvirt support is yet to be added. One issue I faced was that I had to add a pcie root to move virtiofs device off pcie.0 and then hot add remove functionality works. So I had to add pcie root port by adding following to qemu command line. -device pcie-root-port,id=root1,slot=0 And now you can hot add a device using device_add. (qemu) device_add vhost-user-fs-pci,bus=root1,id=myvirtiofs,chardev=char0,tag=myfs,queue-size=1024 - To hot remove device, issue from qemu monitor. (qemu) device_del ex. device_del myvirtiofs Thanks Vivek On Mon, May 03, 2021 at 12:50:56PM +0000, Ge, Xiongzi wrote: > Thanks, Stefan! > It seems that libvirt does not support device-attach for filesystem type device, like virtiofs. Are there any other ways to do this hot-unplugging? > > Xiongzi > > On 4/8/21, 12:21 PM, "Stefan Hajnoczi" wrote: > > On Wed, Apr 07, 2021 at 06:05:29PM +0000, Ge, Xiongzi wrote: > > Thanks Dr Gilbert, Vivek, Stefan, Greg! > > I put together the discussion into this thread and CC qemu-devel@nongnu.org. > > > > Problem: > > Current Virtio-FS does not support live migration. Even when the virtiofs directory is not mounted on the guest, VM cannot do live migration. Any suggestions/interest If we want to make this work so we can still have the live migration feature for other purpose on that VM? > > > > If we already have a shared file system like Ceph, does this make it different? > > (Marc-André: I CCed you regarding D-Bus VMState, see below.) > > During the last virtio-fs call on Wednesday we discussed how to allow > live migration when the file system is not mounted. This means live > migration of a mounted file system still wouldn't be supported, but at > least it would be possible to migrate when the file system is not > mounted. > > The easiest way to do that is to hot unplug the vhost-user-fs-pci device > so that QEMU can live migrate the VM and then hot plug the > vhost-user-fs-pci device again after migration has completed. This > requires either manually performing the hot plug operations or some > automation to do this around live migration. > > A smoother approach would be for QEMU to allow live migration when the > file system is not mounted. Unfortunately it turns out this is actually > rather involved because virtiofsd runs as a separate process from QEMU > and the live migration interface for vhost-user devices is currently > pretty basic > (https://qemu.readthedocs.io/en/latest/interop/dbus-vmstate.html). There > is currently no way for virtiofsd to communicate with QEMU to allow/deny > live migration depending on whether virtiofsd currently has an active > FUSE session (mount). It might be possible to extend the D-Bus VMState > interface and implement support for "migration blockers" as they are > known in QEMU, but I wonder whether it's not better to just work on > full virtio-fs live migration instead. Either task is complex and I > wouldn't recommend it as a first contribution to virtiofsd or QEMU. > > Can you make use of the hotplug approach to live migration? > > Stefan >