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bh=/vU7/rX1RmuOlDxg8zsajDMlz96tOhIoFHNZANkcxJc=; b=U+xlen669Ip8TrRFJJcikIfW31qQxTuD0IHCzayL9N1GHp5svy9eGRh9soAoMZJ55N9R/f LJwtmBwm57iWaOorAS1hgUntvNkgmwi7LFWuKGGcV2HOHKi8q9VbUM30rV382BY0n3bHiJ 4B1bGjFmCvy97u9lhHQ4r7O8x1kGq/0= 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-224-5AY9jjJtMHqC3JvieaKdZA-1; Fri, 02 Oct 2020 11:56:25 -0400 X-MC-Unique: 5AY9jjJtMHqC3JvieaKdZA-1 Received: from smtp.corp.redhat.com (int-mx05.intmail.prod.int.phx2.redhat.com [10.5.11.15]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id B162A186842A; Fri, 2 Oct 2020 15:56:23 +0000 (UTC) Received: from redhat.com (ovpn-114-9.ams2.redhat.com [10.36.114.9]) by smtp.corp.redhat.com (Postfix) with ESMTPS id E87F72C31E; Fri, 2 Oct 2020 15:56:19 +0000 (UTC) Date: Fri, 2 Oct 2020 16:56:17 +0100 From: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= To: Eric Blake Subject: Re: [PATCH v4 9/9] migration: introduce snapshot-{save, load, delete} QMP commands Message-ID: <20201002155617.GN2338114@redhat.com> References: <20200915113523.2520317-1-berrange@redhat.com> <20200915113523.2520317-10-berrange@redhat.com> <87tuvyt9sf.fsf@dusky.pond.sub.org> <0b8eef3d-db87-f82b-798d-2a0cb7ec1198@redhat.com> MIME-Version: 1.0 In-Reply-To: <0b8eef3d-db87-f82b-798d-2a0cb7ec1198@redhat.com> User-Agent: Mutt/1.14.6 (2020-07-11) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.15 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=berrange@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=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 = 2020/10/01 23:37:29 X-ACL-Warn: Detected OS = Linux 2.2.x-3.x [generic] [fuzzy] X-Spam_score_int: -20 X-Spam_score: -2.1 X-Spam_bar: -- X-Spam_report: (-2.1 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.001, 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=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: , Reply-To: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= Cc: Kevin Wolf , Peter Krempa , "Denis V. Lunev" , qemu-block@nongnu.org, Juan Quintela , Markus Armbruster , qemu-devel@nongnu.org, Pavel Dovgalyuk , Paolo Bonzini , Max Reitz , John Snow , "Dr. David Alan Gilbert" Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Mon, Sep 21, 2020 at 01:16:16PM -0500, Eric Blake wrote: > On 9/16/20 3:17 AM, Markus Armbruster wrote: > > Daniel P. Berrangé writes: > > > > > savevm, loadvm and delvm are some of the few HMP commands that have never > > > been converted to use QMP. The reasons for the lack of conversion are > > > that they blocked execution of the event thread, and the semantics > > > around choice of disks were ill-defined. > > > > > > Despite this downside, however, libvirt and applications using libvirt > > > have used these commands for as long as QMP has existed, via the > > > "human-monitor-command" passthrough command. IOW, while it is clearly > > > desirable to be able to fix the problems, they are not a blocker to > > > all real world usage. > > > > > > Meanwhile there is a need for other features which involve adding new > > > parameters to the commands. This is possible with HMP passthrough, but > > > it provides no reliable way for apps to introspect features, so using > > > QAPI modelling is highly desirable. > > > > > > This patch thus introduces new snapshot-{load,save,delete} commands to > > > QMP that are intended to replace the old HMP counterparts. The new > > > commands are given different names, because they will be using the new > > > QEMU job framework and thus will have diverging behaviour from the HMP > > > originals. It would thus be misleading to keep the same name. > > > > > > While this design uses the generic job framework, the current impl is > > > still blocking. The intention that the blocking problem is fixed later. > > > None the less applications using these new commands should assume that > > > they are asynchronous and thus wait for the job status change event to > > > indicate completion. > > > > > > In addition to using the job framework, the new commands require the > > > caller to be explicit about all the block device nodes used in the > > > snapshot operations, with no built-in default heuristics in use. > > > > > > Signed-off-by: Daniel P. Berrangé > > [...] > > > diff --git a/qapi/job.json b/qapi/job.json > > > index 280c2f76f1..b2cbb4fead 100644 > > > --- a/qapi/job.json > > > +++ b/qapi/job.json > > > @@ -22,10 +22,17 @@ > > > # > > > # @amend: image options amend job type, see "x-blockdev-amend" (since 5.1) > > > # > > > +# @snapshot-load: snapshot load job type, see "snapshot-load" (since 5.2) > > > +# > > > +# @snapshot-save: snapshot save job type, see "snapshot-save" (since 5.2) > > > +# > > > +# @snapshot-delete: snapshot delete job type, see "snapshot-delete" (since 5.2) > > > +# > > > # Since: 1.7 > > > ## > > > { 'enum': 'JobType', > > > - 'data': ['commit', 'stream', 'mirror', 'backup', 'create', 'amend'] } > > > + 'data': ['commit', 'stream', 'mirror', 'backup', 'create', 'amend', > > > + 'snapshot-load', 'snapshot-save', 'snapshot-delete'] } > > > ## > > > # @JobStatus: > > > diff --git a/qapi/migration.json b/qapi/migration.json > > > index 675f70bb67..b584c0be31 100644 > > > --- a/qapi/migration.json > > > +++ b/qapi/migration.json > > > @@ -1720,3 +1720,123 @@ > > > ## > > > { 'event': 'UNPLUG_PRIMARY', > > > 'data': { 'device-id': 'str' } } > > > + > > > +## > > > +# @snapshot-save: > > > +# > > > +# Save a VM snapshot > > > +# > > > +# @job-id: identifier for the newly created job > > > +# @tag: name of the snapshot to create > > > +# @devices: list of block device node names to save a snapshot to > > > > Looks like you dropped the idea to also accept drive IDs. Is that for > > good, or would you like to add it later? > > Is it necessary? Several of our newer block interfaces have required node > names, rather than permitting alternation. If we rewrite the existing HMP > commands to operate on top of the new QMP command, it is still possible for > HMP to support drive names even when QMP does not. I don't think the > complexity of worrying about drive names is worth it; after all, the QMP > command is new enough that the only libvirt that will use it is also a > libvirt that knows how to use -blockdev, and thus node names are sufficient. > > Yes, we can add drive ids later if I turn out to be wrong, but for now, I'm > hoping their exclusion is intentional. I didn't realize we have precedent for new commands only accepting node names. Given that, I'm going to stick with this design and only support node names. Regards, Daniel -- |: https://berrange.com -o- https://www.flickr.com/photos/dberrange :| |: https://libvirt.org -o- https://fstop138.berrange.com :| |: https://entangle-photo.org -o- https://www.instagram.com/dberrange :|