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envelope-from=andrey.shinkevich@virtuozzo.com; helo=EUR01-DB5-obe.outbound.protection.outlook.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/07/15 18:19:05 X-ACL-Warn: Detected OS = Windows NT kernel [generic] [fuzzy] X-Spam_score_int: -37 X-Spam_score: -3.8 X-Spam_bar: --- X-Spam_report: (-3.8 / 5.0 requ) BAYES_00=-1.9, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, MSGID_FROM_MTA_HEADER=0.001, RCVD_IN_DNSWL_LOW=-0.7, RCVD_IN_MSPIKE_H2=-1, SPF_HELO_PASS=-0.001, SPF_PASS=-0.001, URIBL_BLOCKED=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: Kevin Wolf , Vladimir Sementsov-Ogievskiy , qemu-devel@nongnu.org Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On 16.07.2020 00:22, Andrey Shinkevich wrote: > On 25.06.2020 18:21, Max Reitz wrote: >> If the top node's driver does not provide snapshot functionality and we >> want to fall back to a node down the chain, we need to snapshot all >> non-COW children.  For simplicity's sake, just do not fall back if there > > I guess it comes to COW children like BDRV_CHILD_DATA | > BDRV_CHILD_METADATA  rather than non-COW ones, does it? > The BDRV_CHILD_COW is mutually exclusive with DATA, METADATA and FILTERED per definition. Sorry about the question. > Andrey > > >> is more than one such child.  Furthermore, we really only can fall back >> to bs->file and bs->backing, because bdrv_snapshot_goto() has to modify >> the child link (notably, set it to NULL). >> >> Suggested-by: Vladimir Sementsov-Ogievskiy >> Signed-off-by: Max Reitz >> --- >>   block/snapshot.c | 104 +++++++++++++++++++++++++++++++++++++---------- >>   1 file changed, 83 insertions(+), 21 deletions(-) >> >> diff --git a/block/snapshot.c b/block/snapshot.c > ... >> +    /* >> +     * Check that there are no other children that would need to be >> +     * snapshotted.  If there are, it is not safe to fall back to >> +     * *fallback. >> +     */ >> +    QLIST_FOREACH(child, &bs->children, next) { >> +        if (child->role & (BDRV_CHILD_DATA | BDRV_CHILD_METADATA | >> +                           BDRV_CHILD_FILTERED) && >> +            child != *fallback) >> +        { >> +            return NULL; >> +        } >> +    } >> + >> +    return fallback; >> +} > > ... > > Reviewed-by: Andrey Shinkevich > >