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

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?

quasi-ACK, your call depending on your comfort level.