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bh=T9LY7V734PnvOmhOkhR3bPQMtuTwCSz0b/uOMK0z1VM=; b=YSmpQnZv2ICIugjo8+kFIhnMo+P97tbNW+CM9QLEZfNGhQDYsGfb3OacYasQwulJ2XTJ3S Lef3o2iESlBZhZp3CMRRz+UifbnsW4ciqW08sTI8ezy8EpXhwnvm1wPQbhDyhDd1R/BO5n DYsmypcUWLxj71NhozyI6taEYadyHYU= 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-582-kZvMiTGNOUm2Xybgsd02jg-1; Fri, 11 Jun 2021 07:21:49 -0400 X-MC-Unique: kZvMiTGNOUm2Xybgsd02jg-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 A97D88015A4; Fri, 11 Jun 2021 11:21:48 +0000 (UTC) Received: from redhat.com (ovpn-114-101.ams2.redhat.com [10.36.114.101]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 4DA256091A; Fri, 11 Jun 2021 11:21:47 +0000 (UTC) Date: Fri, 11 Jun 2021 13:21:45 +0200 From: Kevin Wolf To: Vladimir Sementsov-Ogievskiy Subject: Re: [PATCH] qemu-{img,nbd}: Don't report zeroed cluster as a hole Message-ID: References: <20210607202204.1805199-1-nsoffer@redhat.com> <20210607212224.tiqjvvdwosvhrvz7@redhat.com> <20210610183443.clk43ngkobzyjopy@redhat.com> <20210610204617.fuj4ivqrixpz4qfj@redhat.com> <49ed9c03-eb24-4e8a-1b5f-8a291466a7b9@virtuozzo.com> MIME-Version: 1.0 In-Reply-To: <49ed9c03-eb24-4e8a-1b5f-8a291466a7b9@virtuozzo.com> X-Scanned-By: MIMEDefang 2.79 on 10.5.11.13 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=kwolf@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=170.10.133.124; envelope-from=kwolf@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -29 X-Spam_score: -3.0 X-Spam_bar: --- X-Spam_report: (-3.0 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.199, 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: Nir Soffer , qemu-block , QEMU Developers , Max Reitz , Nir Soffer , Eric Blake Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" Am 11.06.2021 um 10:14 hat Vladimir Sementsov-Ogievskiy geschrieben: > 11.06.2021 11:09, Kevin Wolf wrote: > > Am 10.06.2021 um 22:46 hat Eric Blake geschrieben: > > > On Thu, Jun 10, 2021 at 11:09:05PM +0300, Nir Soffer wrote: > > > > > But: > > > > > > > > > > $ qemu-img map --output=json -f qcow2 json:'{"driver":"qcow2","backing":null, \ > > > > > "file":{"driver":"file","filename":"top.qcow2"}}' > > > > > [{ "start": 0, "length": 65536, "depth": 0, "zero": true, "data": false}, > > > > > { "start": 65536, "length": 65536, "depth": 0, "zero": false, "data": true, "offset": 327680}, > > > > > { "start": 131072, "length": 131072, "depth": 0, "zero": true, "data": false}] > > > > > > > > > > also reports the entire file at "depth":0, which is misleading, since > > > > > we have just been arguing from the qemu:allocation-depth perspective > > > > > (and also from bdrv_block_status) that the qcow2 image is NOT 100% > > > > > allocated (in the sense where allocation == data comes locally). > > > > > Perhaps it might be better if we tweaked the above qemu-img map to > > > > > produce: > > > > > > > > > > [{ "start": 0, "length": 65536, "depth": -1, "zero": true, "data": false}, > > > > > { "start": 65536, "length": 65536, "depth": 0, "zero": false, "data": true, "offset": 327680}, > > > > > { "start": 131072, "length": 65536, "depth": 0, "zero": true, "data": false}, > > > > > { "start": 196608, "length": 65536, "depth": -1, "zero": true, "data": false}] > > > > > > > > It will be more consistent with "offset" to drop "depth" from output > > > > if we don't have it: > > > > > > > > [{ "start": 0, "length": 65536, "zero": true, "data": false}, > > > > { "start": 65536, "length": 65536, "depth": 0, "zero": false, > > > > "data": true, "offset": 327680}, > > > > { "start": 131072, "length": 65536, "depth": 0, "zero": true, > > > > "data": false}, > > > > { "start": 196608, "length": 65536, "zero": true, "data": false}] > > > > > > Yes, that might work as well. But we didn't previously document > > > depth to be optional. Removing something from output risks breaking > > > more downstream tools that expect it to be non-optional, compared to > > > providing a new value. > > > > A negative value isn't any less unexpected than a missing key. I don't > > think any existing tool would be able to handle it. Encoding different > > meanings in a single value isn't very QAPI-like either. Usually strings > > that are parsed are the problem, but negative integers really isn't that > > much different. I don't really like this solution. > > > > Leaving out the depth feels like a better suggestion to me. > > > > But anyway, this seems to only happen at the end of the backing chain. > > So if the backing chain consistents of n images, why not report 'depth': > > n + 1? So, in the above example, you would get 1. I think this has the > > best chances of tools actually working correctly with the new output, > > even though it's still not unlikely to break something. > > > > Did you consider just add a new field? > > So, "depth" keeps its meaning "which level provides data". > > And we add additional optional field like > > absolutely-completely-absent: bool > > Which is true if data is nowhere in the backing chain. Or how about exposing BDRV_BLOCK_ALLOCATED as 'allocated': 'bool'? Which I think is what the conclusion was already for NBD, so doing the same in 'qemu-img map' would be consistent. This is, of course, almost the same as 'absolutely-completely-absent', just without the negating the flag. Kevin