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bh=vbBl4ZNiMKEeDDzGQMNl8lzU/gHb7LBdvpTujTjbWt4=; b=FtqISmh01uNoPxWyIdhjxnIZLOyyNEUXN1BgMlXDW36UYdV89WDnqD+DFh7v4gDjSnGNnM xbKuLow0r0UElqwD3QFIFjqYRqC22aqmqlKACCQTimhtCjUQqgptN4C7oz5GR7mgu6G61s eXsqJMwNyqUZoTZ3nui0iQduCQ+33iw= 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-428-1xBb3ytYOzC4tzWkJ7pwcw-1; Wed, 27 Jan 2021 13:41:51 -0500 X-MC-Unique: 1xBb3ytYOzC4tzWkJ7pwcw-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 5F9081005504; Wed, 27 Jan 2021 18:41:50 +0000 (UTC) Received: from redhat.com (ovpn-115-120.ams2.redhat.com [10.36.115.120]) by smtp.corp.redhat.com (Postfix) with ESMTPS id EFAC517C5F; Wed, 27 Jan 2021 18:41:48 +0000 (UTC) Date: Wed, 27 Jan 2021 18:41:46 +0000 From: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= To: Michal Privoznik Subject: Re: [PATCH v3] machine: add missing doc for memory-backend option Message-ID: <20210127184146.GA3653144@redhat.com> References: <20210121161504.1007247-1-imammedo@redhat.com> <20210127104511.GF3653144@redhat.com> <20210127105436.GG3653144@redhat.com> <756c025a-3811-4a36-98a2-3a02bd756523@redhat.com> <20210127163522.5a8db09a@redhat.com> <20210127175645.GW3653144@redhat.com> <2714b6bd-00f5-6232-a602-f12ea2a4ede0@redhat.com> MIME-Version: 1.0 In-Reply-To: <2714b6bd-00f5-6232-a602-f12ea2a4ede0@redhat.com> User-Agent: Mutt/1.14.6 (2020-07-11) 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 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-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=-0.308, 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: , Reply-To: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= Cc: Igor Mammedov , pkrempa@redhat.com, qemu-devel@nongnu.org, pbonzini@redhat.com, peter.maydell@linaro.org Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Wed, Jan 27, 2021 at 07:30:24PM +0100, Michal Privoznik wrote: > On 1/27/21 6:56 PM, Daniel P. Berrangé wrote: > > On Wed, Jan 27, 2021 at 04:35:22PM +0100, Igor Mammedov wrote: > > > On Wed, 27 Jan 2021 15:24:26 +0100 > > > Michal Privoznik wrote: > > > > > > > On 1/27/21 11:54 AM, Daniel P. Berrangé wrote: > > > > > On Wed, Jan 27, 2021 at 10:45:11AM +0000, Daniel P. Berrangé wrote: > > > > > > On Thu, Jan 21, 2021 at 11:15:04AM -0500, Igor Mammedov wrote: > > > > > > > > > > > > > > > > > > > > How does a mgmt app know which machine types need to use this > > > > > > option ? The machine type names are opaque strings, and apps > > > > > > must not attempt to parse or interpret the version number > > > > > > inside the machine type name, as they can be changed by > > > > > > distros. IOW, saying to use it for machine types 4.0 and > > > > > > older isn't a valid usage strategy IMHO. > > > it's possible (but no necessary) to use knob with new machine types > > > (defaults for these match suggested property value). > > > > IIUC, this means that setting the property has no impact on > > migration ABI for new machine types > 4.0.... > > > > > Limiting knob usage to 4.0 and older would allow us to drop > > > without extra efforts once 4.0 is deprecated/removed. > > > > ...so, even if we set the property unconditionally for *all* > > machine types, then we can still remove it in future, becuase > > its removal won't affect ABI of the 5.x, 6.x machine types. > > Alright, so after all you agree with proposed patch? I'm a bit confused. + b) for machine types 4.0 and older, user shall + use ``x-use-canonical-path-for-ramblock-id=off`` backend option + if migration to/from old QEMU (<5.0) is expected. instead of refering to machine type versions, I think it could say something more like b) if the ``x-use-canonical-path-for-ramblock-id`` property exists, it should be set to ``off``, if migration to/from old QEMU (<5.0) is expected. Assuming it genuinely does not have any ABI impact on new machine types. 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 :|