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Wed, 23 Jun 2021 09:35:58 -0700 (PDT) X-Google-Smtp-Source: ABdhPJzGzhswfHswbEgJDKDqFbU5PPXS36mxFTpEld/cr6KwltfGAvONLZq9Rz93bcZDgLNUCWfKWINcnyplVy0T0rw= X-Received: by 2002:a9d:6250:: with SMTP id i16mr707840otk.170.1624466158172; Wed, 23 Jun 2021 09:35:58 -0700 (PDT) MIME-Version: 1.0 References: <20210611140157.1366738-1-eblake@redhat.com> <20210611190316.1424729-1-eblake@redhat.com> In-Reply-To: From: Nir Soffer Date: Wed, 23 Jun 2021 19:35:42 +0300 Message-ID: Subject: Re: [PATCH v2 2/1] qemu-img: Add "backing":true to unallocated map segments To: Kevin Wolf Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=nsoffer@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset="UTF-8" Received-SPF: pass client-ip=170.10.133.124; envelope-from=nsoffer@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -31 X-Spam_score: -3.2 X-Spam_bar: --- X-Spam_report: (-3.2 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.373, 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: Vladimir Sementsov-Ogievskiy , "open list:Block layer core" , Markus Armbruster , QEMU Developers , Max Reitz , Eric Blake Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Wed, Jun 23, 2021 at 7:04 PM Kevin Wolf wrote: > > Am 23.06.2021 um 15:58 hat Nir Soffer geschrieben: > > On Wed, Jun 23, 2021 at 11:58 AM Kevin Wolf wrote: > > > > > > Am 22.06.2021 um 18:56 hat Nir Soffer geschrieben: > > > > On Tue, Jun 22, 2021 at 6:38 PM Kevin Wolf wrote: > > > > > > > > > > Am 11.06.2021 um 21:03 hat Eric Blake geschrieben: > > > > > > To save the user from having to check 'qemu-img info --backing-chain' > > > > > > or other followup command to determine which "depth":n goes beyond the > > > > > > chain, add a boolean field "backing" that is set only for unallocated > > > > > > portions of the disk. > > > > > > > > > > > > Signed-off-by: Eric Blake > > > > > > --- > > > > > > > > > > > > Touches the same iotest output as 1/1. If we decide that switching to > > > > > > "depth":n+1 is too risky, and that the mere addition of "backing":true > > > > > > while keeping "depth":n is good enough, then we'd have just one patch, > > > > > > instead of this double churn. Preferences? > > > > > > > > > > I think the additional flag is better because it's guaranteed to be > > > > > backwards compatible, and because you don't need to know the number of > > > > > layers to infer whether a cluster was allocated in the whole backing > > > > > chain. And by exposing ALLOCATED we definitely give access to the whole > > > > > information that exists in QEMU. > > > > > > > > > > However, to continue with the bike shedding: I won't insist on > > > > > "allocated" even if that is what the flag is called internally and > > > > > consistency is usually helpful, but "backing" is misleading, too, > > > > > because intuitively it doesn't cover the top layer or standalone images > > > > > without a backing file. How about something like "present"? > > > > > > > > Looks hard to document: > > > > > > > > # @present: if present and false, the range is not allocated within the > > > > # backing chain (since 6.1) > > > > > > I'm not sure why you would document it with a double negative. > > > > > > > And is not consistent with "offset". It would work better as: > > > > > > > > # @present: if present, the range is allocated within the backing > > > > # chain (since 6.1) > > > > > > Completely ignoring the value? I would have documented it like this, but > > > with "if true..." instead of "if present...". > > > > This is fine, but it means that this flag will present in all ranges, > > instead of only in unallocated ranges (what this patch is doing). > > An argument for always having the flag would be that it's probably > useful for a tool to know whether a given block is actually absent or > whether it's just running an old qemu-img. Good point, this is the best option. The disadvantage is a bigger output but if you use json you don't care about the size of the output. > If we didn't care about this, I would still define the actual value, but > also document a default. > > Kevin >