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

[Laine Stump]

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.