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bh=qzOm2DmuuR/9Ie19niGExs/IYglc8i+tCED3cG83MII=; b=g1XM8lMAXqSjCK863l1wKEjOWacqFvKZ2uy/rtHFpVJRbdtYZGATaYbDPGYaIDY5btjLFZ moIpleYjQ3IZ6+tmHISpF77OQj/sHtjqsiMp0YXf5VpWJofKx4GwReufIODY6HVaYgAbtd suUHx12mlmgEW5IUgeNjRPRVqu4QAW4= X-MC-Unique: cWEZkKQUM2Cx1fclbO2U5Q-1 From: Max Reitz <mreitz@redhat.com> To: qemu-block@nongnu.org Subject: [PULL 11/22] qcow2: Rewrite the documentation of qcow2_alloc_cluster_offset() Date: Tue, 15 Sep 2020 12:46:16 +0200 Message-Id: <20200915104627.699552-12-mreitz@redhat.com> In-Reply-To: <20200915104627.699552-1-mreitz@redhat.com> References: <20200915104627.699552-1-mreitz@redhat.com> MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.84 on 10.5.11.23 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=mreitz@redhat.com X-Mimecast-Spam-Score: 0.001 X-Mimecast-Originator: redhat.com Content-Transfer-Encoding: quoted-printable Received-SPF: pass (zohomail.com: domain of gnu.org designates 209.51.188.17 as permitted sender) client-ip=209.51.188.17; envelope-from=qemu-devel-bounces+importer=patchew.org@nongnu.org; helo=lists.gnu.org; Received-SPF: pass client-ip=63.128.21.124; envelope-from=mreitz@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/09/15 02:23:19 X-ACL-Warn: Detected OS = Linux 2.2.x-3.x [generic] [fuzzy] X-Spam_score_int: -38 X-Spam_score: -3.9 X-Spam_bar: --- X-Spam_report: (-3.9 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-1.792, 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=unavailable autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: <qemu-devel.nongnu.org> List-Unsubscribe: <https://lists.nongnu.org/mailman/options/qemu-devel>, <mailto:qemu-devel-request@nongnu.org?subject=unsubscribe> List-Archive: <https://lists.nongnu.org/archive/html/qemu-devel> List-Post: <mailto:qemu-devel@nongnu.org> List-Help: <mailto:qemu-devel-request@nongnu.org?subject=help> List-Subscribe: <https://lists.nongnu.org/mailman/listinfo/qemu-devel>, <mailto:qemu-devel-request@nongnu.org?subject=subscribe> Cc: Peter Maydell <peter.maydell@linaro.org>, qemu-devel@nongnu.org, Max Reitz <mreitz@redhat.com> Errors-To: qemu-devel-bounces+importer=patchew.org@nongnu.org Sender: "Qemu-devel" <qemu-devel-bounces+importer=patchew.org@nongnu.org> X-ZohoMail-DKIM: fail (Header signature does not verify) Content-Type: text/plain; charset="utf-8" From: Alberto Garcia <berto@igalia.com> The current text corresponds to an earlier, simpler version of this function and it does not explain how it works now. Signed-off-by: Alberto Garcia <berto@igalia.com> Message-Id: <bb5bd06f07c5a05b0818611de0d06ec5b66c8df3.1599150873.git.berto@= igalia.com> Signed-off-by: Max Reitz <mreitz@redhat.com> --- block/qcow2-cluster.c | 24 ++++++++++++++---------- 1 file changed, 14 insertions(+), 10 deletions(-) diff --git a/block/qcow2-cluster.c b/block/qcow2-cluster.c index f65ccc5840..ce1260e746 100644 --- a/block/qcow2-cluster.c +++ b/block/qcow2-cluster.c @@ -1714,18 +1714,22 @@ out: } =20 /* - * alloc_cluster_offset + * For a given area on the virtual disk defined by @offset and @bytes, + * find the corresponding area on the qcow2 image, allocating new + * clusters (or subclusters) if necessary. The result can span a + * combination of allocated and previously unallocated clusters. * - * For a given offset on the virtual disk, find the cluster offset in qcow2 - * file. If the offset is not found, allocate a new cluster. + * On return, @host_offset is set to the beginning of the requested + * area. This area is guaranteed to be contiguous on the qcow2 file + * but it can be smaller than initially requested. In this case @bytes + * is updated with the actual size. * - * If the cluster was already allocated, m->nb_clusters is set to 0 and - * other fields in m are meaningless. - * - * If the cluster is newly allocated, m->nb_clusters is set to the number = of - * contiguous clusters that have been allocated. In this case, the other - * fields of m are valid and contain information about the first allocated - * cluster. + * If any clusters or subclusters were allocated then @m contains a + * list with the information of all the affected regions. Note that + * this can happen regardless of whether this function succeeds or + * not. The caller is responsible for updating the L2 metadata of the + * allocated clusters (on success) or freeing them (on failure), and + * for clearing the contents of @m afterwards in both cases. * * If the request conflicts with another write request in flight, the coro= utine * is queued and will be reentered when the dependency has completed. --=20 2.26.2