From: Kevin Wolf <kwolf@redhat.com>
To: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
Cc: John Snow <jsnow@redhat.com>, qemu-devel <qemu-devel@nongnu.org>,
Qemu-block <qemu-block@nongnu.org>, Max Reitz <mreitz@redhat.com>
Subject: Re: bitmap migration bug with -drive while block mirror runs
Date: Tue, 1 Oct 2019 18:16:10 +0200 [thread overview]
Message-ID: <20191001161610.GG4688@linux.fritz.box> (raw)
In-Reply-To: <9431d242-bfe1-b9db-17d0-6c1a280a05da@virtuozzo.com>
Am 01.10.2019 um 17:57 hat Vladimir Sementsov-Ogievskiy geschrieben:
> 01.10.2019 17:10, John Snow wrote:
> >
> >
> > On 10/1/19 10:00 AM, Vladimir Sementsov-Ogievskiy wrote:
> >>> Otherwise: I have a lot of cloudy ideas on how to solve this, but
> >>> ultimately what we want is to be able to find the "addressable" name for
> >>> the node the bitmap is attached to, which would be the name of the first
> >>> ancestor node that isn't a filter. (OR, the name of the block-backend
> >>> above that node.)
> >> Not the name of ancestor node, it will break mapping: it must be name of the
> >> node itself or name of parent (may be through several filters) block-backend
> >>
> >
> > Ah, you are right of course -- because block-backends are the only
> > "nodes" for which we actually descend the graph and add the bitmap to
> > its child.
> >
> > So the real back-resolution mechanism is:
> >
> > - Find the first non-filter ancestor, A
> > - if A is not a block-backend, we must use our node-local name.
> > - if A's name is empty, we must use our node-local name.
> > - If the name we have chosen is not id_wellformed, we have no
> > migration-stable addressable name for this bitmap and the migration must
> > fail!
> >
> >
> > For resolving bitmap addresses via QMP (node, name) pairs; the
> > resolution method would be this:
> >
> > - if the node-name N is a block-backend, descend the tree until we find
> > the first non-filter node V.
> > - if the node-name N is a BlockDriverState, use this node directly.
> >
>
> Looks good for me.
>
> I also think if on destination we have both block-backend with name N and
> block-node with name N and the latter is not (filtered) child of the former,
> we should fail migration of at least that bitmap. (Hope, nobody reuse
> block-backend names as node-names in practice.. (should we restrict it
> explicitly ?))
You can't have a node and a BlockBackend of the same name, they share a
single namespace. If you try to do so, you get an error.
Kevin
next prev parent reply other threads:[~2019-10-01 16:41 UTC|newest]
Thread overview: 47+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-10-01 0:09 bitmap migration bug with -drive while block mirror runs John Snow
2019-10-01 4:28 ` Peter Krempa
2019-10-01 9:07 ` Vladimir Sementsov-Ogievskiy
2019-10-01 8:57 ` Vladimir Sementsov-Ogievskiy
2019-10-01 9:54 ` Kevin Wolf
2019-10-01 10:05 ` Vladimir Sementsov-Ogievskiy
2019-10-01 13:24 ` Peter Krempa
2019-10-01 15:09 ` John Snow
2019-10-01 15:58 ` Kevin Wolf
2019-10-01 16:12 ` Vladimir Sementsov-Ogievskiy
2019-10-01 16:24 ` Kevin Wolf
2019-10-01 16:23 ` John Snow
2019-10-01 11:45 ` Peter Krempa
2019-10-01 9:17 ` Vladimir Sementsov-Ogievskiy
2019-10-01 14:00 ` Vladimir Sementsov-Ogievskiy
2019-10-01 14:10 ` John Snow
2019-10-01 15:57 ` Vladimir Sementsov-Ogievskiy
2019-10-01 16:07 ` John Snow
2019-10-02 8:12 ` Kevin Wolf
2019-10-02 10:46 ` Peter Krempa
2019-10-02 11:11 ` Kevin Wolf
2019-10-02 12:22 ` Vladimir Sementsov-Ogievskiy
2019-10-02 13:48 ` Peter Krempa
2019-10-02 13:43 ` Peter Krempa
2019-10-02 14:03 ` Vladimir Sementsov-Ogievskiy
2019-10-02 21:35 ` John Snow
2019-10-03 10:14 ` Vladimir Sementsov-Ogievskiy
2019-10-03 23:34 ` John Snow
2019-10-04 8:33 ` Peter Krempa
2019-10-04 9:21 ` Vladimir Sementsov-Ogievskiy
2019-10-06 3:15 ` John Snow
2019-10-04 9:24 ` Vladimir Sementsov-Ogievskiy
2019-10-04 13:07 ` Eric Blake
2019-10-06 3:19 ` John Snow
2019-10-01 16:16 ` Kevin Wolf [this message]
2019-10-01 16:17 ` Vladimir Sementsov-Ogievskiy
2019-10-01 14:13 ` Max Reitz
2019-10-01 14:27 ` Vladimir Sementsov-Ogievskiy
2019-10-01 14:34 ` Max Reitz
2019-10-01 14:53 ` Vladimir Sementsov-Ogievskiy
2019-10-01 15:26 ` Max Reitz
2019-10-02 7:34 ` Peter Krempa
2019-10-01 15:09 ` Kevin Wolf
2019-10-01 15:27 ` Max Reitz
2019-10-01 16:12 ` Kevin Wolf
2019-10-01 16:17 ` Max Reitz
2019-10-01 16:22 ` Vladimir Sementsov-Ogievskiy
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