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From: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
To: John Snow <jsnow@redhat.com>
Cc: Peter Krempa <pkrempa@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 15:57:48 +0000	[thread overview]
Message-ID: <9431d242-bfe1-b9db-17d0-6c1a280a05da@virtuozzo.com> (raw)
In-Reply-To: <4bc910ef-0bec-cfd6-89f6-a93d35367218@redhat.com>

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 ?))

> 
> (I don't have the time to investigate the code snippet right now; my
> attention is being pulled to a different project. sorry!)
> 

So, you are not working on this? Then I'll make patches.

-- 
Best regards,
Vladimir

  reply	other threads:[~2019-10-01 16:50 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 [this message]
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
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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