Re: [libvirt] [PATCH] qmp: Deprecate query-nodes option of query-blockstats
Am 28.01.2019 um 17:12 hat Daniel P. Berrangé geschrieben:
On Mon, Jan 28, 2019 at 04:37:50PM +0100, Kevin Wolf wrote:
> Am 28.01.2019 um 16:15 hat Anton Kuchin geschrieben:
> > This option is broken since a6baa60807 in v2.9 and returns mostly
> > zeroes instead of real stats because actual querring of BlockStats
> > that resides in blk is missing.
> >
> > And it makes no sense because with this option BlockDriverState-s
> > are iterated but BlockAcctStats belong to BlockBackend and not BDS
> > since 7f0e9da6f13 in v2.5
> >
> > Signed-off-by: Anton Kuchin <antonkuchin(a)yandex-team.ru>
>
> Isn't query-nodes the only way to get wr_highest_offset for the protocol
> layer? oVirt depends on this, as far as I know.
Libvirt just invokes 'query-blockstats' with no arguments, so is not
relying on 'query-nodes' working. Given that libvirt doesn't use it,
it doesn't seem like this is relevant for oVirt unless they were
using QMP passthrough from libvirt. That this has been broken
since v2.9 though rather suggests oVirt doesn't use it.
It's not broken at all. The type of the return value is just a bit messy
because we mix statistics from the device with statistics from the
nodes. query-nodes=true can't return device statistics, but the
respective fields aren't optional in the schema either, so it just puts
0 there. This is ugly, but if you know which information you can use, it
works fine, so cleaning it up was never considered to have a good
justification for breaking compatibility.
In any case, wr_highest_offset is part of the node statistics and it
contains the correct value for each node.
Kevin