From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:54507) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1Vo4so-0003zh-P0 for qemu-devel@nongnu.org; Wed, 04 Dec 2013 00:20:28 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1Vo4si-0004mV-KC for qemu-devel@nongnu.org; Wed, 04 Dec 2013 00:20:22 -0500 Received: from nodalink.pck.nerim.net ([62.212.105.220]:43629 helo=paradis.irqsave.net) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1Vo4si-0004mN-2o for qemu-devel@nongnu.org; Wed, 04 Dec 2013 00:20:16 -0500 Date: Wed, 4 Dec 2013 06:20:06 +0100 From: =?iso-8859-1?Q?Beno=EEt?= Canet Message-ID: <20131204052006.GB2781@irqsave.net> References: <1386077165-19577-1-git-send-email-benoit@irqsave.net> <1386077165-19577-7-git-send-email-benoit@irqsave.net> <529EA5CA.6050608@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <529EA5CA.6050608@redhat.com> Content-Transfer-Encoding: quoted-printable Subject: Re: [Qemu-devel] [RFC V3 6/7] block: Create authorizations mechanism for external snapshots. List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Fam Zheng Cc: kwolf@redhat.com, jcody@redhat.com, qemu-devel@nongnu.org, armbru@redhat.com, stefanha@redhat.com Le Wednesday 04 Dec 2013 =C3=A0 11:47:22 (+0800), Fam Zheng a =C3=A9crit = : > On 2013=E5=B9=B412=E6=9C=8803=E6=97=A5 21:26, Beno=C3=AEt Canet wrote: > >--- > > block.c | 64 +++++++++++++++++++++++++++++++++++++= ++++------ > > block/blkverify.c | 2 +- > > include/block/block.h | 16 +++++++++--- > > include/block/block_int.h | 9 ++++--- > > 4 files changed, 75 insertions(+), 16 deletions(-) > > > >diff --git a/block.c b/block.c > >index 8016ff2..0569cb2 100644 > >--- a/block.c > >+++ b/block.c > >@@ -4945,21 +4945,69 @@ int bdrv_amend_options(BlockDriverState *bs, Q= EMUOptionParameter *options) > > return bs->drv->bdrv_amend_options(bs, options); > > } > > > >-ExtSnapshotPerm bdrv_check_ext_snapshot(BlockDriverState *bs) > >+/* will be used to recurse on single child block filter until first f= ormat > >+ * (single child block filter will store their child in bs->file) > >+ */ > >+ExtSnapshotPerm bdrv_generic_check_ext_snapshot(BlockDriverState *bs, > >+ BlockDriverState *can= didate) > > { > >- if (bs->drv->bdrv_check_ext_snapshot) { > >- return bs->drv->bdrv_check_ext_snapshot(bs); > >+ if (!bs->drv) { > >+ return EXT_SNAPSHOT_FORBIDDEN; > > } > > > >- if (bs->file && bs->file->drv && bs->file->drv->bdrv_check_ext_sn= apshot) { > >- return bs->file->drv->bdrv_check_ext_snapshot(bs); > >+ if (!bs->drv->authorizations[BS_CANT_SNAPSHOT]) { >=20 > This double negative feels hard to read for me. >=20 > >+ if (bs =3D=3D candidate) { > >+ return EXT_SNAPSHOT_ALLOWED; > >+ } else { > >+ return EXT_SNAPSHOT_FORBIDDEN; > >+ } > > } > > > >- /* external snapshots are allowed by default */ > >- return EXT_SNAPSHOT_ALLOWED; > >+ if (!bs->drv->authorizations[BS_FILTER_PASS_DOWN]) { > >+ return EXT_SNAPSHOT_FORBIDDEN; > >+ } > >+ > >+ if (!bs->file) { > >+ return EXT_SNAPSHOT_FORBIDDEN; > >+ } > >+ > >+ return bdrv_recurse_check_ext_snapshot(bs->file, candidate); > > } > > > >-ExtSnapshotPerm bdrv_check_ext_snapshot_forbidden(BlockDriverState *b= s) > >+ExtSnapshotPerm bdrv_recurse_check_ext_snapshot(BlockDriverState *bs, > >+ BlockDriverState *can= didate) > > { > >+ if (bs->drv && bs->drv->bdrv_check_ext_snapshot) { > >+ return bs->drv->bdrv_check_ext_snapshot(bs, candidate); > >+ } >=20 > Maybe I'm missing something, but if a driver always returns positive > permit, despite of what candidate is (or even it's relevant to bs), > then doesn't it also affect other devices? because... >=20 > >+ > >+ return bdrv_generic_check_ext_snapshot(bs, candidate); > >+} > >+ > >+/* This function check if the candidate bs has snapshots authorized b= y going > >+ * down the forest of bs, skipping filters and stopping on the the fi= rst bses > >+ * authorizing snapshots > >+ */ > >+ExtSnapshotPerm bdrv_check_ext_snapshot(BlockDriverState *candidate) > >+{ > >+ BlockDriverState *bs; > >+ > >+ /* walk down the bs forest recursively */ > >+ QTAILQ_FOREACH(bs, &bdrv_states, device_list) { >=20 > this iterates through all the known graph trees (device_list), > instead of limiting to only the device that candidate belongs to. The recursion termination success is candidate =3D=3D bs. This make sure that the scan of the other tree of the forest will not ret= urn any spurious success. >=20 > Why not just check candidate's permission bitmap and go down from > it? If an ancestor need to disable its descendants, it could simply > set permission bits of its children and recurse down. Yes I initially though about updating permission bit of each bs. The problem is that the graph will evolve (taking a snapshot, adding thro= ttling filter) and it would be a mess to constansly update the permission bits. Best regards Beno=C3=AEt >=20 > Fam