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=-3.6 required=3.0 tests=BAYES_00,DKIM_INVALID, DKIM_SIGNED,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS 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 E1D9DC433DF for ; Thu, 27 Aug 2020 11:17:09 +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 B0AB122B40 for ; Thu, 27 Aug 2020 11:17:09 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="KcAhpnWi" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org B0AB122B40 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]:58896 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1kBFu0-0005Im-TC for qemu-devel@archiver.kernel.org; Thu, 27 Aug 2020 07:17:08 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:54184) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1kBFtG-00049O-1W for qemu-devel@nongnu.org; Thu, 27 Aug 2020 07:16:22 -0400 Received: from us-smtp-delivery-124.mimecast.com ([63.128.21.124]:57439) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_CBC_SHA1:256) (Exim 4.90_1) (envelope-from ) id 1kBFtC-0000mZ-Qa for qemu-devel@nongnu.org; Thu, 27 Aug 2020 07:16:21 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1598526977; 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: content-transfer-encoding:content-transfer-encoding; bh=jQAWyHKD6x1jC9LbOgFnarxu5345NQX/mkh71dpnMNs=; b=KcAhpnWi25lIoVph8gFVjM0K2u2vWIRrnzyIyVG7pyZgokNx/cW3glCQnVsxzgaazbz059 Qko7YmS6vjyuDpn15uKgB+XULHcX6zoUpVLsYLmu0WpSTOhK2Mrf/wZFyI5dx2pLJKk1hT xWVZmzuiOcE859Thy8HglgdRjsFBU1M= 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-552-0tYRaKu3P3OfiYOuSKDP6g-1; Thu, 27 Aug 2020 07:16:13 -0400 X-MC-Unique: 0tYRaKu3P3OfiYOuSKDP6g-1 Received: from smtp.corp.redhat.com (int-mx01.intmail.prod.int.phx2.redhat.com [10.5.11.11]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 0901D420E7; Thu, 27 Aug 2020 11:16:12 +0000 (UTC) Received: from localhost.localdomain.com (unknown [10.36.110.51]) by smtp.corp.redhat.com (Postfix) with ESMTP id 909B5757EC; Thu, 27 Aug 2020 11:16:08 +0000 (UTC) From: =?UTF-8?q?Daniel=20P=2E=20Berrang=C3=A9?= To: qemu-devel@nongnu.org Subject: [PATCH v3 0/7] migration: bring improved savevm/loadvm/delvm to QMP Date: Thu, 27 Aug 2020 12:15:59 +0100 Message-Id: <20200827111606.1408275-1-berrange@redhat.com> MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.79 on 10.5.11.11 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=berrange@redhat.com X-Mimecast-Spam-Score: 0.004 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: quoted-printable Received-SPF: pass client-ip=63.128.21.124; envelope-from=berrange@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/08/27 02:54:02 X-ACL-Warn: Detected OS = Linux 2.2.x-3.x [generic] [fuzzy] X-Spam_score_int: -30 X-Spam_score: -3.1 X-Spam_bar: --- X-Spam_report: (-3.1 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.959, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H5=0.001, RCVD_IN_MSPIKE_WL=0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=unavailable 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: Kevin Wolf , Peter Krempa , =?UTF-8?q?Daniel=20P=2E=20Berrang=C3=A9?= , "Denis V. Lunev" , qemu-block@nongnu.org, Juan Quintela , John Snow , Markus Armbruster , "Dr. David Alan Gilbert" , Pavel Dovgalyuk , Paolo Bonzini , Max Reitz Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" v1: https://lists.gnu.org/archive/html/qemu-devel/2020-07/msg00866.html=0D v2: https://lists.gnu.org/archive/html/qemu-devel/2020-07/msg07523.html=0D =0D When QMP was first introduced some 10+ years ago now, the snapshot=0D related commands (savevm/loadvm/delvm) were not converted. This was=0D primarily because their implementation causes blocking of the thread=0D running the monitor commands. This was (and still is) considered=0D undesirable behaviour both in HMP and QMP.=0D =0D In theory someone was supposed to fix this flaw at some point in the=0D past 10 years and bring them into the QMP world. Sadly, thus far it=0D hasn't happened as people always had more important things to work=0D on. Enterprise apps were much more interested in external snapshots=0D than internal snapshots as they have many more features.=0D =0D Meanwhile users still want to use internal snapshots as there is=0D a certainly simplicity in having everything self-contained in one=0D image, even though it has limitations. Thus the apps that end up=0D executing the savevm/loadvm/delvm via the "human-monitor-command"=0D QMP command.=0D =0D IOW, the problematic blocking behaviour that was one of the reasons=0D for not having savevm/loadvm/delvm in QMP is experienced by applications=0D regardless. By not portting the commands to QMP due to one design flaw,=0D we've forced apps and users to suffer from other design flaws of HMP (=0D bad error reporting, strong type checking of args, no introspection) for=0D an additional 10 years. This feels rather sub-optimal :-(=0D =0D In practice users don't appear to care strongly about the fact that these= =0D commands block the VM while they run. I might have seen one bug report=0D about it, but it certainly isn't something that comes up as a frequent=0D topic except among us QEMU maintainers. Users do care about having=0D access to the snapshot feature.=0D =0D Where I am seeing frequent complaints is wrt the use of OVMF combined=0D with snapshots which has some serious pain points. This is getting worse=0D as the push to ditch legacy BIOS in favour of UEFI gain momentum both=0D across OS vendors and mgmt apps. Solving it requires new parameters to=0D the commands, but doing this in HMP is super unappealing.=0D =0D After 10 years, I think it is time for us to be a little pragmatic about=0D our handling of snapshots commands. My desire is that libvirt should never= =0D use "human-monitor-command" under any circumstances, because of the=0D inherant flaws in HMP as a protocol for machine consumption.=0D =0D Thus in this series I'm proposing a fairly direct mapping of the existing= =0D HMP commands for savevm/loadvm/delvm into QMP as a first step. This does=0D not solve the blocking thread problem, but it does put in a place a=0D design using the jobs framework which can facilitate solving it later.=0D It does also solve the error reporting, type checking and introspection=0D problems inherant to HMP. So we're winning on 3 out of the 4 problems,=0D and pushed apps to a QMP design that will let us solve the last=0D remaining problem.=0D =0D With a QMP variant, we reasonably deal with the problems related to OVMF:= =0D =0D - The logic to pick which disk to store the vmstate in is not=0D satsifactory.=0D =0D The first block driver state cannot be assumed to be the root disk=0D image, it might be OVMF varstore and we don't want to store vmstate=0D in there.=0D =0D - The logic to decide which disks must be snapshotted is hardwired=0D to all disks which are writable=0D =0D Again with OVMF there might be a writable varstore, but this can be=0D raw rather than qcow2 format, and thus unable to be snapshotted.=0D While users might wish to snapshot their varstore, in some/many/most=0D cases it is entirely uneccessary. Users are blocked from snapshotting=0D their VM though due to this varstore.=0D =0D These are solved by adding two parameters to the commands. The first is=0D a block device node name that identifies the image to store vmstate in,=0D and the second is a list of node names to include for the snapshots.=0D If the list of nodes isn't given, it falls back to the historical=0D behaviour of using all disks matching some undocumented criteria.=0D =0D In the block code I've only dealt with node names for block devices, as=0D IIUC, this is all that libvirt should need in the -blockdev world it now=0D lives in. IOW, I've made not attempt to cope with people wanting to use=0D these QMP commands in combination with -drive args, as libvirt will=0D never use -drive with a QEMU new enough to have these new commands.=0D =0D The main limitations of this current impl=0D =0D - The snapshot process runs serialized in the main thread. ie QEMU=0D guest execution is blocked for the duration. The job framework=0D lets us fix this in future without changing the QMP semantics=0D exposed to the apps.=0D =0D - Most vmstate loading errors just go to stderr, as they are not=0D using Error **errp reporting. Thus the job framework just=0D reports a fairly generic message=0D =0D "Error -22 while loading VM state"=0D =0D Again this can be fixed later without changing the QMP semantics=0D exposed to apps.=0D =0D I've done some minimal work in libvirt to start to make use of the new=0D commands to validate their functionality, but this isn't finished yet.=0D =0D My ultimate goal is to make the GNOME Boxes maintainer happy again by=0D having internal snapshots work with OVMF:=0D =0D https://gitlab.gnome.org/GNOME/gnome-boxes/-/commit/c486da262f6566326fbcb= 5e=3D=0D f45c5f64048f16a6e=0D =0D Changed in v3:=0D =0D - Schedule a bottom half to escape from coroutine context in=0D the jobs. This is needed because the locking in the snapshot=0D code goes horribly wrong when run from a background coroutine=0D instead of the main event thread.=0D =0D - Re-factor way we iterate over devices, so that we correctly=0D report non-existant devices passed by the user over QMP.=0D =0D - Add QAPI docs notes about limitations wrt vmstate error=0D reporting (it all goes to stderr not an Error **errp)=0D so QMP only gets a fairly generic error message currently.=0D =0D - Add I/O test to validate many usage scenarios / errors=0D =0D - Add I/O test helpers to handle QMP events with a deterministic=0D ordering=0D =0D - Ensure 'delete-snapshot' reports an error if requesting=0D delete from devices that don't support snapshot, instead of=0D silently succeeding with no erro.=0D =0D Changed in v2:=0D =0D - Use new command names "snapshot-{load,save,delete}" to make it=0D clear that these are different from the "savevm|loadvm|delvm"=0D as they use the Job framework=0D =0D - Use an include list for block devs, not an exclude list=0D =0D Daniel P. Berrang=3DC3=3DA9 (7):=0D migration: improve error reporting of block driver state name=0D block: push error reporting into bdrv_all_*_snapshot functions=0D migration: stop returning errno from load_snapshot()=0D block: add ability to specify list of blockdevs during snapshot=0D block: allow specifying name of block device for vmstate storage=0D iotests: add support for capturing and matching QMP events=0D migration: introduce snapshot-{save,load,delete} QMP commands=0D =0D block/monitor/block-hmp-cmds.c | 7 +-=0D block/snapshot.c | 233 ++++++++++++++-------=0D include/block/snapshot.h | 19 +-=0D include/migration/snapshot.h | 10 +-=0D migration/savevm.c | 258 +++++++++++++++++++----=0D monitor/hmp-cmds.c | 11 +-=0D qapi/job.json | 9 +-=0D qapi/migration.json | 135 ++++++++++++=0D replay/replay-snapshot.c | 4 +-=0D softmmu/vl.c | 2 +-=0D tests/qemu-iotests/267.out | 14 +-=0D tests/qemu-iotests/310 | 255 +++++++++++++++++++++++=0D tests/qemu-iotests/310.out | 369 +++++++++++++++++++++++++++++++++=0D tests/qemu-iotests/common.qemu | 107 +++++++++-=0D tests/qemu-iotests/group | 1 +=0D 15 files changed, 1289 insertions(+), 145 deletions(-)=0D create mode 100755 tests/qemu-iotests/310=0D create mode 100644 tests/qemu-iotests/310.out=0D =0D --=3D20=0D 2.26.2=0D =0D