[libvirt] [PATCH RFC 00/39] qemu: Add support for -blockdev

[Peter Krempa]

On Thu, Jul 26, 2018 at 17:04:19 +0800, Fam Zheng wrote:
> On Thu, 07/26 10:44, Kevin Wolf wrote:
> > Am 25.07.2018 um 17:57 hat Peter Krempa geschrieben:
> > > This series adds support for starting and hotplug of disks with
> > > -blockdev/blockdev-add.
> > > 
> > > Blockjobs are not supported and thus the last patch should not be
> > > applied yet as some refactoring of the jobs is required.
> > > 
> > > At the beginning of the series there are a few cleanup patches which may
> > > be pushed even at this point.
> > > 
> > > The main reason this is in RFC state is that block stats reporting does
> > > not work.
> > > 
> > > The following command:
> > > 
> > > {"execute":"query-blockstats","arguments":{"query-nodes":true}}
> > 
> > query-nodes was added in commit f71eaa74c0b by Fam and Max, CCed. I'm
> > not sure what it was needed for at all and the commit message doesn't
> > help with that, but I suppose the addition was related to
> > wr_highest_offset (see below).
> 
> Yes, this was part of RHBZ 1158094. Sorry about the poor commit message.

Well the problem is that when using -blockdev with 'query-nodes' false/not present you get a
even more useless output:

virsh qemu-monitor-command --pretty upstream '{"execute":"query-blockstats","arguments":{"query-nodes":false}}'
{
  "return": [

  ],
  "id": "libvirt-20"
}

'query-named-block-nodes' don't provide the 'stats' section either:
(other drives snipped)

    {
      "iops_rd": 0,
      "detect_zeroes": "off",
      "image": {
        "virtual-size": 520032256,
        "filename": "/var/lib/libvirt/images/systemrescuecd-x86-4.9.5.iso",
        "format": "raw",
        "actual-size": 520036352,
        "dirty-flag": false
      },
      "iops_wr": 0,
      "ro": true,
      "node-name": "libvirt-7-format",
      "backing_file_depth": 0,
      "drv": "raw",
      "iops": 0,
      "bps_wr": 0,
      "write_threshold": 0,
      "encrypted": false,
      "bps": 0,
      "bps_rd": 0,
      "cache": {
        "no-flush": false,
        "direct": false,
        "writeback": true
      },
      "file": "/var/lib/libvirt/images/systemrescuecd-x86-4.9.5.iso",
      "encryption_key_missing": false
    },
    {
      "iops_rd": 0,
      "detect_zeroes": "off",
      "image": {
        "virtual-size": 520032256,
        "filename": "/var/lib/libvirt/images/systemrescuecd-x86-4.9.5.iso",
        "format": "file",
        "actual-size": 520036352,
        "dirty-flag": false
      },
      "iops_wr": 0,
      "ro": true,
      "node-name": "libvirt-7-storage",
      "backing_file_depth": 0,
      "drv": "file",
      "iops": 0,
      "bps_wr": 0,
      "write_threshold": 0,
      "encrypted": false,
      "bps": 0,
      "bps_rd": 0,
      "cache": {
        "no-flush": false,
        "direct": false,
        "writeback": true
      },
      "file": "/var/lib/libvirt/images/systemrescuecd-x86-4.9.5.iso",
      "encryption_key_missing": false
    }
  ],
  "id": "libvirt-19"
}

Thus libvirt can't provide the stats it used to with -drive. Since we
need to special-case the code for gathering stats for -blockdev it
should not be a problem if e.g. query-named-block-nodes reported the
stats section along. (perhaps with a boolean flag to do so which also
could disable the nesting)

In either case we need the stats in the same extent as we had before
with -drive and query-blockstats.
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