Re: [Qemu-devel] [PATCH for-2.10 v3] block: Skip implicit nodes in query-block/blockstats

From: Eric Blake <eblake@redhat.com>
To: Kevin Wolf <kwolf@redhat.com>, qemu-block@nongnu.org
Cc: mreitz@redhat.com, armbru@redhat.com, pkrempa@redhat.com,
	nsoffer@redhat.com, el13635@mail.ntua.gr, qemu-devel@nongnu.org,
	qemu-stable@nongnu.org
Subject: Re: [Qemu-devel] [PATCH for-2.10 v3] block: Skip implicit nodes in query-block/blockstats
Date: Thu, 20 Jul 2017 10:37:50 -0500	[thread overview]
Message-ID: <f03a930c-7352-6e6a-d306-47a0f31c0ee6@redhat.com> (raw)
In-Reply-To: <1500556314-32102-1-git-send-email-kwolf@redhat.com>

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On 07/20/2017 08:11 AM, Kevin Wolf wrote:
> Commits 0db832f and 6cdbceb introduced the automatic insertion of filter
> nodes above the top layer of mirror and commit block jobs. The
> assumption made there was that since libvirt doesn't do node-level
> management of the block layer yet, it shouldn't be affected by added
> nodes.
> 
> This is true as far as commands issued by libvirt are concerned. It only
> uses BlockBackend names to address nodes, so any operations it performs
> still operate on the root of the tree as intended.
> 
> However, the assumption breaks down when you consider query commands,
> which return data for the wrong node now. These commands also return
> information on some child nodes (bs->file and/or bs->backing), which
> libvirt does make use of, and which refer to the wrong nodes, too.
> 
> One of the consequences is that oVirt gets wrong information about the
> image size and stops the VM in response as long as a mirror or commit
> job is running:
> 
> https://bugzilla.redhat.com/show_bug.cgi?id=1470634
> 
> This patch fixes the problem by hiding the implicit nodes created
> automatically by the mirror and commit block jobs in the output of
> query-block and BlockBackend-based query-blockstats as long as the user
> doesn't indicate that they are aware of those nodes by providing a node
> name for them in the QMP command to start the block job.
> 
> The node-based commands query-named-block-nodes and query-blockstats
> with query-nodes=true still show all nodes, including implicit ones.
> This ensures that users that are capable of node-level management can
> still access the full information; users that only know BlockBackends
> won't use these commands.
> 
> Cc: qemu-stable@nongnu.org
> Signed-off-by: Kevin Wolf <kwolf@redhat.com>
> ---

I ran libvirt against qemu with this patch applied, and tested that I
was able to use the block threshold events through libvirt both on a
domain with no jobs, and then again after I created a mirror job after
setting the threshold (for some reason, libvirt didn't like me setting a
threshold after starting the mirror - but that's a pre-existing
limitation in libvirt).  At any rate, the thresholds behaved the way I
expected, so it looks like libvirt is okay with the change in output.
That, plus your testsuite additions (qemu-iotests passed for me), means
you can add:

Tested-by: Eric Blake <eblake@redhat.com>

-- 
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3266
Virtualization:  qemu.org | libvirt.org

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