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Thu, 10 Jun 2021 06:19:38 -0700 (PDT) X-Google-Smtp-Source: ABdhPJwA7zl7ShbD65QKFYyIJP5koDTszSE7IDQSZ11ImuDSY3bBInUdNiBM/Hp6uFa1r/3a2Uf25djeldblk0QgsYw= X-Received: by 2002:a4a:3796:: with SMTP id r144mr2356216oor.79.1623331178798; Thu, 10 Jun 2021 06:19:38 -0700 (PDT) MIME-Version: 1.0 References: <20210609180118.1003774-1-eblake@redhat.com> <20210609213154.1012848-1-eblake@redhat.com> <20210610130616.nmmckl7v5l5n3agn@redhat.com> In-Reply-To: <20210610130616.nmmckl7v5l5n3agn@redhat.com> From: Nir Soffer Date: Thu, 10 Jun 2021 16:19:22 +0300 Message-ID: Subject: Re: [RFC libnbd PATCH] info: Add support for new qemu:joint-allocation To: Eric Blake 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: -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: qemu-block , Vladimir Sementsov-Ogievskiy , QEMU Developers , libguestfs@redhat.com Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Thu, Jun 10, 2021 at 4:06 PM Eric Blake wrote: > > On Thu, Jun 10, 2021 at 01:20:13AM +0300, Nir Soffer wrote: > > > + else if (strcmp (metacontext, "qemu:joint-allocation") == 0) { > > > + /* Combo of base:allocation and stripped-down qemu:allocation-depth */ > > > + const char *base, *depth; > > > + switch (type & 3) { > > > + case 0: base = "allocated"; break; > > > + case 1: base = "hole"; break; > > > + case 2: base = "zero"; break; > > > + case 3: base = "hole,zero"; break; > > > + } > > > + switch (type & 0xc) { > > > + case 0: depth = "unallocated"; break; > > > > Is this possible? qemu reports BDRV_BLOCK_DATA but not BDRV_BLOCK_ALLOCATED? > > No, qemu should never report a status of 0 (which in this code would > produce the string "allocated,unallocated", although a v2 may change > to print ""). > > Remember, BDRV_BLOCK_ALLOCATED is a bit of a misnomer - it has nothing > to do with whether a cluster occupies allocated space, but rather > whether the local image in the backing chain provides the contents of > the cluster (rather than deferring to the backing chain). The code in > block/io.c guarantees that if a block device reports BDRV_BLOCK_DATA, > then the block layer also reports BDRV_BLOCK_ALLOCATED (that is, any > cluster that provides guest-visible data by necessity implies that the > current layer of the backing chain is important). > > However, it DOES point out that "allocated" might not be the best name > in libnbd; perhaps "data" or "normal" would be better for the NBD > base:allocation status of 0. Yes! it also aligns better with zero, and the output is similar to qemu-img map. Hopefully the semantics of "data" in qemu-img map and libnbd is the same.