qemu-block
[Top][All Lists]
Advanced

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Re: [PATCH v2 0/5] fix migration with bitmaps and mirror


From: Vladimir Sementsov-Ogievskiy
Subject: Re: [PATCH v2 0/5] fix migration with bitmaps and mirror
Date: Fri, 15 May 2020 14:15:22 +0300
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.8.0

15.05.2020 08:52, Vladimir Sementsov-Ogievskiy wrote:
14.05.2020 21:29, Eric Blake wrote:
reviving this thread...

On 4/3/20 6:23 AM, Peter Krempa wrote:
On Fri, Apr 03, 2020 at 14:02:47 +0300, Vladimir Sementsov-Ogievskiy wrote:
19.12.2019 13:36, Peter Krempa wrote:
On Thu, Dec 19, 2019 at 11:51:01 +0300, Vladimir Sementsov-Ogievskiy wrote:
Hi all!

It's a continuation for
"bitmap migration bug with -drive while block mirror runs"
<address@hidden>
https://lists.gnu.org/archive/html/qemu-devel/2019-09/msg07241.html

The problem is that bitmaps migrated to node with same node-name or
blk-parent name. And currently only the latter actually work in libvirt.
And with mirror-top filter it doesn't work, because
bdrv_get_device_or_node_name don't go through filters.

I want to point out that since libvirt-5.10 we use -blockdev to
configure the backend of storage devices with qemu-4.2 and later. This
means unfortunately that the BlockBackend of the drive does not have a
name any more and thus the above will not work even if you make the
lookup code to see through filters.

Not that this series doesn't make things worse, as it loops through named
block backends when trying to use their name for migration. So with these
patches applied, qemu will just work in more possible scenarios.

Okay, if that's so it's fair enough in this case.

I'm just very firmly against baking in the assumption that
node names mean the same thing accross migration, because that will
create a precedent situation and more stuff may be baked in on top of
this in the future. It seems that it has already happened though and
it's wrong. And the worst part is that it's never mentioned that this
might occur. But again, don't do that and preferrably remove the
matching of node names for bitmaps altogether until we can control it
arbitrarily.

We've also seen this already before with the backend name of memory
devices being baked in to the migration stream which creates an unwanted
dependancy.

Max is trying to tackle the node-name issue:
https://lists.gnu.org/archive/html/qemu-devel/2020-05/msg03358.html

And trying to apply that patch after staging this series hits a conflict in 
mnigration/block-dirty-bitmap.c.  Which one should go in first?


My patches are needed to fix migration for the pre-blockdev configuration with 
mirror-top filter.

We ofcrouse need them in Virtuozzo, but it's not hard to keep the in 
downstream-only.. And it will be not simple to use new command from Max in 
pre-blockdev libvirt configuration, with auto-generated node-names.

How much we care about pre-blockdev libvirt now in upstream Qemu?

If we don't care, than these series are only for downstreams, and we don't need 
to apply them upstream..

On the other hand, Max have to resend anyway, to handle old code, which uses 
device name instead of node-name. And if we don't want to drop now the code 
which can use device name (needed for old libvirt), why not to apply the 
series, which just make old code better?

====

In other words: do we still support pre-blockdev libvirt (and any other 
pre-blockdev users)?

If we support, than, as I said somewhere, I need to resend these series as I 
have updated version in our downstream. And I think, I can rebase Max's patch 
by myself and send together with this all, if no objections.


I'm going to resend the series today, let's look at it.

--
Best regards,
Vladimir



reply via email to

[Prev in Thread] Current Thread [Next in Thread]