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=-8.5 required=3.0 tests=BAYES_00,DKIM_INVALID, DKIM_SIGNED,HEADER_FROM_DIFFERENT_DOMAINS,LOTS_OF_MONEY,MAILING_LIST_MULTI, MENTIONS_GIT_HOSTING,MONEY_NOHTML,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED, USER_AGENT_SANE_1 autolearn=ham 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 82960C433ED for ; Thu, 13 May 2021 08:27:52 +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 CFB2D6135A for ; Thu, 13 May 2021 08:27:51 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org CFB2D6135A Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Received: from localhost ([::1]:45028 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1lh6hC-0005NC-OK for qemu-devel@archiver.kernel.org; Thu, 13 May 2021 04:27:50 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:34866) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1lh6g5-0004PO-9u for qemu-devel@nongnu.org; Thu, 13 May 2021 04:26:41 -0400 Received: from us-smtp-delivery-124.mimecast.com ([216.205.24.124]:43679) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1lh6g0-000132-RR for qemu-devel@nongnu.org; Thu, 13 May 2021 04:26:40 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1620894394; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=nibr0W2FoUiYbsC6Or3e6j8+kvxv7oLVcYROcNwipQU=; b=U4fAS01AP2yImpoHD1sjmOgAPMd4kakNVpd1RxpH9O2oajZNBNzHEQkcM8BJGDNIel6iuT NWeJTJitSq0S1SeM1ywuh3UrS7tFftZUApsKvZJaKN46vgD/s8nBE93rSnmfkrR/ljqnV9 r0f/EKZH+BfaASMqUn9OUl0SMmAZE7c= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-97-p0EzlBafPsWxvCMZ1yABWA-1; Thu, 13 May 2021 04:26:31 -0400 X-MC-Unique: p0EzlBafPsWxvCMZ1yABWA-1 Received: from smtp.corp.redhat.com (int-mx03.intmail.prod.int.phx2.redhat.com [10.5.11.13]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 210BB6D4F9; Thu, 13 May 2021 08:26:30 +0000 (UTC) Received: from work-vm (ovpn-113-200.ams2.redhat.com [10.36.113.200]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 509B56E407; Thu, 13 May 2021 08:26:25 +0000 (UTC) Date: Thu, 13 May 2021 09:26:22 +0100 From: "Dr. David Alan Gilbert" To: Jiachen Zhang Subject: Re: [Virtio-fs] host-user reconnection and crash recovery Message-ID: References: MIME-Version: 1.0 In-Reply-To: User-Agent: Mutt/2.0.6 (2021-03-06) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.13 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=dgilbert@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Received-SPF: pass client-ip=216.205.24.124; envelope-from=dgilbert@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -18 X-Spam_score: -1.9 X-Spam_bar: - X-Spam_report: (-1.9 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.7, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, LOTS_OF_MONEY=0.001, MONEY_NOHTML=1.636, 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" , Yongji Xie , "Boeuf, Sebastien" , "qemu-devel@nongnu.org" , fam.zheng@bytedance.com Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" * Jiachen Zhang (zhangjiachen.jaycee@bytedance.com) wrote: > Hi Stefan and Sebastien, > > I think I should give some background context from my perspective. > > For the virtiofsd crash reconnection (recovery) to QEMU, as said by > Stefan, we discussed the possible implementation on the bi-weekly virtio-fs > call. I had also sent an RFC patch to the virtio-fs mail-list ( > https://patchwork.kernel.org/project/qemu-devel/cover/20201215162119.27360-1-zhangjiachen.jaycee@bytedance.com/), > we also have some discussion on the further revision direction in that > mail. > > We also have some needs to support virtiofsd crash recovery when it is used > with cloud-hypervisor (https://github.com/cloud-hypervisor/cloud-hypervisor). > However, the virtiofsd crash reconnection RFC patch relies on > QEMU's vhost-user socket reconnection feature and QEMU's vhost-user > inflight I/O tracking feature, which are both not supported by > cloud-hypervisor. > > So I also issued an initial pull-request of cloud-hypervisor vhost-user > socket reconnection ( > https://github.com/cloud-hypervisor/cloud-hypervisor/pull/2387), which is > reviewed by Sebastien. Based on vhost-user socket reconnection, we also > want to further develop vhost-user inflight I/O tracking feature for > cloud-hypervisor, and finally to support virtiofsd crash reconnection. > > I am sorry for the delayed patch-revision of the two patch sets. I hope I > can free up some time in these two months to make some further progress. I'm curious what your use case is for virtiofsd crash recovery/reconnection - is there some reason you expect the daemon to crash or need to be restarted more than the whole VM? In the case of vhost-user networking with dpdk I can see the case where there is a central networking switch process shared between many VMs; so wanting to restart that without restarting all the VMs makes sense to me; where each VM has it's own virtiofsd I don't understand the use as much. Dave > All the best, > Jiachen > > On Tue, May 11, 2021 at 11:02 PM Boeuf, Sebastien > wrote: > > > Hi Stefan, > > > > Thanks for the explanation. > > > > So reconnection for vhost-user is not a well defined behavior, > > and QEMU is doing its best to retry when possible, depending > > on each device. > > > > The guest does not know about it, so it's never notified that > > the device needs to be reset. > > > > But what about the vhost-user backend initialization? Does > > QEMU go again through initializing memory table, vrings, etc... > > since it can't assume anything from the backend? > > > > Thanks, > > Sebastien > > > > ------------------------------ > > *From:* Stefan Hajnoczi > > *Sent:* Tuesday, May 11, 2021 2:45 PM > > *To:* Boeuf, Sebastien > > *Cc:* virtio-fs@redhat.com; qemu-devel@nongnu.org > > *Subject:* vhost-user reconnection and crash recovery > > > > Hi Sebastien, > > On #virtio-fs IRC you asked: > > > > I have a vhost-user question regarding disconnection/reconnection. How > > should this be handled? Let's say the vhost-user backend disconnects, > > and reconnects later on, does QEMU reset the virtio device by notifying > > the guest? Or does it simply reconnects to the backend without letting > > the guest know about what happened? > > > > The vhost-user protocol does not have a generic reconnection solution. > > Reconnection is handled on a case-by-case basis because device-specific > > and implementation-specific state is involved. > > > > The vhost-user-fs-pci device in QEMU has not been tested with > > reconnection as far as I know. > > > > The ideal reconnection behavior is to resume the device from its > > previous state without disrupting the guest. Device state must survive > > reconnection in order for this to work. Neither QEMU virtiofsd nor > > virtiofsd-rs implement this today. > > > > virtiofs has a lot of state, making it particularly difficult to support > > either DEVICE_NEEDS_RESET or transparent vhost-user reconnection. We > > have discussed virtiofs crash recovery on the bi-weekly virtiofs call > > (https://etherpad.opendev.org/p/virtiofs-external-meeting). If you want > > to work on this then joining the call would be a good starting point to > > coordinate with others. > > > > One approach for transparent crash recovery is for virtiofsd to keep its > > state in tmpfs (e.g. inode/fd mappings) and open fds shared with a > > clone(2) process via CLONE_FILES. This way the virtiofsd process can > > terminate but its state persists in memory thanks to its clone process. > > The clone can then be used to launch the new virtiofsd process from the > > old state. This would allow the device to resume transparently with QEMU > > only reconnecting the vhost-user UNIX domain socket. This is an idea > > that we discussed in the bi-weekly virtiofs call. > > > > You mentioned device reset. VIRTIO 1.1 has the Device Status Field > > DEVICE_NEEDS_RESET flat that the device can use to tell the driver that > > a reset is necessary. This feature is present in the specification but > > not implemented in the Linux guest drivers. Again the reason is that > > handling it requires driver-specific logic for restoring state after > > reset...otherwise the device reset would be visible to userspace. > > > > Stefan > > > > --------------------------------------------------------------------- > > Intel Corporation SAS (French simplified joint stock company) > > Registered headquarters: "Les Montalets"- 2, rue de Paris, > > 92196 Meudon Cedex, France > > Registration Number: 302 456 199 R.C.S. NANTERRE > > Capital: 4,572,000 Euros > > > > This e-mail and any attachments may contain confidential material for > > the sole use of the intended recipient(s). Any review or distribution > > by others is strictly prohibited. If you are not the intended > > recipient, please contact the sender and delete all copies. > > _______________________________________________ > > Virtio-fs mailing list > > Virtio-fs@redhat.com > > https://listman.redhat.com/mailman/listinfo/virtio-fs > > > _______________________________________________ > Virtio-fs mailing list > Virtio-fs@redhat.com > https://listman.redhat.com/mailman/listinfo/virtio-fs -- Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK