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Lunev" Cc: qemu-devel@nongnu.org, qemu-block@nongnu.org, Andrey Drobyshev , Hanna Reitz , qemu-stable@nongnu.org Subject: Re: [PATCH v4 1/5] qcow2: do not clear the dirty bit when reopening a read-only node Message-ID: References: <20260824133729.1141990-1-den@openvz.org> <20260824133729.1141990-2-den@openvz.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260824133729.1141990-2-den@openvz.org> X-Scanned-By: MIMEDefang 3.0 on 10.30.177.12 Received-SPF: pass client-ip=170.10.129.124; envelope-from=kwolf@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: 10 X-Spam_score: 1.0 X-Spam_bar: + X-Spam_report: (1.0 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.24, 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_H2=0.001, RCVD_IN_SBL_CSS=3.335, SPF_HELO_PASS=-0.001, SPF_PASS=-0.001 autolearn=no autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: qemu development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Am 24.08.2026 um 15:37 hat Denis V. Lunev geschrieben: > From: Denis V. Lunev > > qcow2_reopen_prepare() clears the dirty bit whenever the node is > reopened read-only, with an unguarded header write. A read-only node > can still be dirty, inherited from an earlier writable session, and it > holds no BLK_PERM_WRITE to resolve that. A read-only to read-only > reopen of a dirty image therefore fails outright: > > $ qemu-io -r -f qcow2 dirty.qcow2 <<< $'reopen -r\nquit' > qemu-io: failed while preparing to reopen image 'dirty.qcow2' > > Where the file node below is writable the write is not refused early, > and bdrv_co_write_req_prepare() aborts on its BLK_PERM_WRITE assertion > instead. > > Clear it only for a node that is writable now, the predicate > qcow2_do_open() already uses for the repair. bdrv_is_writable() also > excludes an inactive node, whose header must not be touched either. > > Signed-off-by: Denis V. Lunev > Reviewed-by: Andrey Drobyshev > CC: Kevin Wolf > CC: Hanna Reitz > CC: Andrey Drobyshev > Cc: qemu-stable@nongnu.org Reviewed-by: Kevin Wolf