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Re: [PATCH v2 4/5] migration/block-dirty-bitmap: fix bitmaps migration d
From: |
Eric Blake |
Subject: |
Re: [PATCH v2 4/5] migration/block-dirty-bitmap: fix bitmaps migration during mirror job |
Date: |
Thu, 14 May 2020 13:52:36 -0500 |
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Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.7.0 |
On 12/19/19 2:51 AM, Vladimir Sementsov-Ogievskiy wrote:
Important thing for bitmap migration is to select destination block
node to obtain the migrated bitmap.
Prepatch, on source we use bdrv_get_device_or_node_name() to identify
the node, and on target we do bdrv_lookup_bs.
bdrv_get_device_or_node_name() returns blk name only for direct
children of blk. So, bitmaps of direct children of blks are migrated by
blk name and others - by node name.
Libvirt currently is unprepared to bitmap migration by node-name,
node-names are mostly auto-generated. So actually only migration by blk
name works.
It depends on whether -blockdev is in use. With -blockdev, libvirt
should be supplying a node name everywhere, without, it is only device
names.
Now, consider classic libvirt migrations assisted by mirror block job:
mirror block job inserts filter, so our source is not a direct child of
blk, and bitmaps are migrated by node-names. And this just don't work.
Does Max' work to improve seeing through filters fix this?
Let's fix it by allowing use blk-name even if some implicit filters are
inserted.
Note, that we possibly want to allow explicit filters skipping too, but
this is another story.
Note2: we, of course, can't skip filters and use blk name to migrate
bitmaps in filtered node by blk name for this blk if these filters have
named bitmaps which should be migrated.
Fixes: https://bugzilla.redhat.com/show_bug.cgi?id=1652424
That bug has been marked CLOSED in the meantime, but it appears to be
only because libvirt is now using -blockdev rather than the older drive,
while the problem affects drive usage.
Signed-off-by: Vladimir Sementsov-Ogievskiy <address@hidden>
---
migration/block-dirty-bitmap.c | 39 +++++++++++++++++++++++++++++++++-
1 file changed, 38 insertions(+), 1 deletion(-)
Okay, after reading some more history on this project (the curse of
coming up to speed after volunteering to become a co-maintainer), it
looks like Max's idea replaces this patch altogether. How much of the
rest of the series is still important?
--
Eric Blake, Principal Software Engineer
Red Hat, Inc. +1-919-301-3226
Virtualization: qemu.org | libvirt.org
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