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Mon, 11 Nov 2019 16:02:48 +0000 (UTC) From: Max Reitz To: qemu-block@nongnu.org Subject: [PATCH for-5.0 v2 10/23] quorum: Implement .bdrv_recurse_can_replace() Date: Mon, 11 Nov 2019 17:02:03 +0100 Message-Id: <20191111160216.197086-11-mreitz@redhat.com> In-Reply-To: <20191111160216.197086-1-mreitz@redhat.com> References: <20191111160216.197086-1-mreitz@redhat.com> MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.79 on 10.5.11.13 X-MC-Unique: P4zVO02qNYSj50LgzzNASQ-1 X-Mimecast-Spam-Score: 0 Content-Type: text/plain; charset=WINDOWS-1252 Content-Transfer-Encoding: quoted-printable X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic] [fuzzy] X-Received-From: 207.211.31.81 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 , Alberto Garcia , qemu-devel@nongnu.org, Max Reitz Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" Signed-off-by: Max Reitz --- block/quorum.c | 62 ++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 62 insertions(+) diff --git a/block/quorum.c b/block/quorum.c index 3a824e77e3..8ee03e9baf 100644 --- a/block/quorum.c +++ b/block/quorum.c @@ -825,6 +825,67 @@ static bool quorum_recurse_is_first_non_filter(BlockDr= iverState *bs, return false; } =20 +static bool quorum_recurse_can_replace(BlockDriverState *bs, + BlockDriverState *to_replace) +{ + BDRVQuorumState *s =3D bs->opaque; + int i; + + for (i =3D 0; i < s->num_children; i++) { + /* + * We have no idea whether our children show the same data as + * this node (@bs). It is actually highly likely that + * @to_replace does not, because replacing a broken child is + * one of the main use cases here. + * + * We do know that the new BDS will match @bs, so replacing + * any of our children by it will be safe. It cannot change + * the data this quorum node presents to its parents. + * + * However, replacing @to_replace by @bs in any of our + * children's chains may change visible data somewhere in + * there. We therefore cannot recurse down those chains with + * bdrv_recurse_can_replace(). + * (More formally, bdrv_recurse_can_replace() requires that + * @to_replace will be replaced by something matching the @bs + * passed to it. We cannot guarantee that.) + * + * Thus, we can only check whether any of our immediate + * children matches @to_replace. + * + * (In the future, we might add a function to recurse down a + * chain that checks that nothing there cares about a change + * in data from the respective child in question. For + * example, most filters do not care when their child's data + * suddenly changes, as long as their parents do not care.) + */ + if (s->children[i].child->bs =3D=3D to_replace) { + Error *local_err =3D NULL; + + /* + * We now have to ensure that there is no other parent + * that cares about replacing this child by a node with + * potentially different data. + */ + s->children[i].to_be_replaced =3D true; + bdrv_child_refresh_perms(bs, s->children[i].child, &local_err)= ; + + /* Revert permissions */ + s->children[i].to_be_replaced =3D false; + bdrv_child_refresh_perms(bs, s->children[i].child, &error_abor= t); + + if (local_err) { + error_free(local_err); + return false; + } + + return true; + } + } + + return false; +} + static int quorum_valid_threshold(int threshold, int num_children, Error *= *errp) { =20 @@ -1195,6 +1256,7 @@ static BlockDriver bdrv_quorum =3D { =20 .is_filter =3D true, .bdrv_recurse_is_first_non_filter =3D quorum_recurse_is_first_non_fi= lter, + .bdrv_recurse_can_replace =3D quorum_recurse_can_replace, =20 .strong_runtime_opts =3D quorum_strong_runtime_opts, }; --=20 2.23.0