[libvirt] [PATCH 12/13] qemu: only add channel arg to scsi-disk if qemu binary supports it

[Laine Stump]

On 05/14/2015 12:25 PM, Laine Stump wrote:
> On 05/08/2015 09:44 PM, John Ferlan wrote:
>> On 05/05/2015 02:03 PM, Laine Stump wrote:
>>> libvirt enforces bus (channel to qemu) == 0 for those qemu binaries
>>> that don't support the channel argument to scsi disk devices, but
>>> still adds "channel=0" in those cases. Apparently nobody with a qemu
>>> old enough to not support channel ever uses these devices, because
>>> they otherwise should get an error.
>>>
>>> This patch only adds channel when the scsi-disk.channel capability is
>>> set for the qemu binary. Most of the change in the patch is updating
>>> patches to either 1) remove channel=0 from the .args file of the test,
>>> or 2) reposition channel=0 to precede the bus arg (because this makes
>>> the code cleaner/simpler) and change the DO_TEST() invocation for the
>>> test to add QEMU_CAPS_SCSI_DISK_CHANNEL.
>>>
>>> I'm uncommitted about whether or not it is worthwhile to push this
>>> patch. On one hand, I'm fairly certain this is what is correct; on the
>>> other hand nobody has ever complained about it, and at this point
>>> almost everyone is using new enough qemu that it supports channel.
>>> ---
>>>  src/qemu/qemu_command.c                            |  7 +++---
>>>  .../qemuxml2argv-disk-drive-network-iscsi-lun.args |  2 +-
>>>  .../qemuxml2argv-disk-scsi-disk-split.args         |  8 +++----
>>>  .../qemuxml2argv-disk-scsi-disk-vpd.args           |  2 +-
>>>  .../qemuxml2argv-disk-scsi-disk-wwn.args           |  4 ++--
>>>  .../qemuxml2argv-disk-scsi-lun-passthrough.args    |  4 ++--
>>>  .../qemuxml2argv-disk-scsi-megasas.args            |  2 +-
>>>  .../qemuxml2argv-disk-scsi-virtio-scsi.args        |  2 +-
>>>  .../qemuxml2argv-disk-scsi-vscsi.args              |  2 +-
>>>  .../qemuxml2argv-disk-virtio-scsi-ccw.args         |  2 +-
>>>  .../qemuxml2argv-disk-virtio-scsi-cmd_per_lun.args |  2 +-
>>>  .../qemuxml2argv-disk-virtio-scsi-max_sectors.args |  2 +-
>>>  .../qemuxml2argv-disk-virtio-scsi-num_queues.args  |  2 +-
>>>  .../qemuxml2argv-pseries-vio-user-assigned.args    |  2 +-
>>>  .../qemuxml2argvdata/qemuxml2argv-pseries-vio.args |  2 +-
>>>  tests/qemuxml2argvtest.c                           | 25 +++++++++++++---------
>>>  16 files changed, 38 insertions(+), 32 deletions(-)
>>>
>> I'm in agreement with you vis-a-vis whether it's worthwhile. Nothing's
>> broken, so the axiom may apply. However, we don't know if it's broken
>> "under the covers" since we don't know the affect of adding channel=# to
>> a qemu that doesn't support it since we don't seem to have one of those
>> today.
>>
>> OTOH since you added the QEMU_CAPS_SCSI_DISK_CHANNEL bit in and that
>> alone didn't break anything, then it would appear this change should be
>> OK.  Other than changing the order/placement of channel (which seems to
>> be a non-issue), it seems these changes are fine.
>>
>> Should I assume you've started guests with all these changes? And
>> perhaps restart libvirtd to make sure noone disappears?
> I did restart libvirtd with a running guest with SCSI disk, no problems,
> and then destroyed and restart the guest (so it uses the different
> argument ordering), no problems. I don't have a reasonable way to test
> the case when channel= isn't supported, since that has even been
> backported to RHEL6.
>
>> quasi-ACK, your call depending on your comfort level.
> I'm planning on pushing this later today, if there are no objections.

Along with RHEL6/CentOS6 supporting channel, RHEL5 is old enough that it
doesn't even support -device, so I have nothing of the proper vintage to
test for non-support of channel, and this makes me doubt that anybody
anywhere has a system that would be affected by this patch, so I'm
dropping it too.