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

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.