[libvirt] [PATCH] rng: tighten up domain <controller> schema

Osier Yang jyang at redhat.com
Fri Apr 19 08:33:04 UTC 2013


On 18/04/13 19:59, Laine Stump wrote:
> On 04/18/2013 07:27 AM, Osier Yang wrote:
>> On 18/04/13 19:16, Laine Stump wrote:
>>> On 04/18/2013 05:41 AM, Martin Kletzander wrote:
>>>> On 04/18/2013 11:05 AM, Osier Yang wrote:
>>>>> On 18/04/13 17:00, Martin Kletzander wrote:
>>>>>> On 04/18/2013 10:54 AM, Osier Yang wrote:
>>>>>>> On 18/04/13 16:42, Martin Kletzander wrote:
>>>>>>>> On 04/18/2013 06:36 AM, Laine Stump wrote:
>>>>>>>>> The rng schema for <controller> had been non-specific about which
>>>>>>>>> types of controllers allowed which models, and also allowed the
>>>>>>>>> num_queues attribute (since that hasn't been released yet,
>>>>>>>>> should we
>>>>>>>>> rename it to "numQueues"?)
>>>>>>>> Since there's still time (the commit with that is
>>>>>>>> v1.0.4-65-gd4bf0a9), I
>>>>>>>> think we should rename it ASAP since we are using camelCase for
>>>>>>>> all the
>>>>>>>> attribute names.
>>>>>>>>
>>>>>>>> Apart from that, the RNG with this patch is precise according to
>>>>>>>> the
>>>>>>>> documentation, so ACK.  I'll try to send the numQueues patch to see
>>>>>>>> what
>>>>>>>> others think.
>>>>>>> I guess you mean multiple queues support for virtio network?
>>>>>>> Regardless of which style we will use finally, FYI,  "num_queues" is
>>>>>>> used for disk.. Personally I'm fine with either, because we already
>>>>>>> use both across.
>>>>>>>
>>>>>> Yes, I meant the virtio-scsi num_queues.  As we're trying not to use
>>>>>> underscores in XML, I hope we can still switch it.  I haven't
>>>>>> found any
>>>>>> other num_queues anywhere in the code.  Could you point me to the
>>>>>> commit
>>>>>> that uses that?  I'm sending the previously discussed patch in the
>>>>>> meantime.
>>>>>>
>>>>> Except the virtio-scsi num_queues, there is no other tag for multiple
>>>>> queue yet, we will need a patch to support multiple queue for the
>>>>> network,
>>>>> but it's not committed yet.
>>>>>
>>>>> It's fine to convert it now, 1.0.5 is not released yet. But is it
>>>>> deserved to
>>>>> do, we already have many tags with underscore, which can't be changed
>>>>> for back-compat.
>>>>>
>>>> I believe those attributes [1] were created by mistake, and kept only
>>>> because of backward compatibility.  I'm trying to be open-minded,
>>>> though, so I'm not forcing my patch in, but seeing it just as a
>>>> proposal.  Others may have different opinions and I'm willing to
>>>> discuss
>>>> that.  My first feeling, though, was that we should try to keep the
>>>> same
>>>> policy for as many of them as possible.  OTOH, I've mistaken the
>>>> underscore with a hyphen when I remembered what Daniel told me about
>>>> attributes [2].
>>> I had recalled DV saying something about underscores in the names a long
>>> time ago, and I recently asked about underscore vs. camelCase, and danpb
>>> said the same thing. (Personally I don't have a preference one way or
>>> the other, but if we really are trying to avoid them, now is our
>>> chance).
>> I'm fine with either keeping it or changing num_queues. For long
>> term consistence, I agreed with having a consistent naming style
>> is nice.
>>
>>> In the meantime, in other device types, we've tried to keep backend
>>> details like this pushed into a <driver> subelement when possible, to
>>> avoid polluting the main element (e.g. see the <driver> subelement of
>>> <interface>). Is it worth putting this numQueues attribute in a <driver>
>>> subelement too? Or am I just playing XML God?
>> Not sure if you mean the upcoming numQueues for interface. But for the
>> existing num_queues, it's for the virtio-scsi controller, putting it
>> in <driver>
>> doesn't reflect the purpose.
>
> But isn't it a backend implementation detail of the specific SCSI
> controller? In <interface> and <disk>, information that is specific to a
> particular backend (and isn't generally applicable to that type of
> device) is in the <driver> subelement.

This is the QEMU command line for a virtio-scsi disk: ("-device 
virtio-scsi-pci"
is mapped to virtio-scsi controller in libvirt XML, with num_queues set):
<...>
-device virtio-scsi-pci,id=scsi0,num_queues=8,bus=pci.0,addr=0x3 \
-usb \
-drive file=/dev/HostVG/QEMUGuest1,if=none,id=drive-scsi0-0-0-0 \
-device 
scsi-disk,bus=scsi0.0,channel=0,scsi-id=0,lun=0,drive=drive-scsi0-0-0-0,id=scsi0-0-0-0 
\
</...>


And this is the QEMU command line for a virtio disk (with event_idx set):
<...>
-drive file=/var/lib/libvirt/images/f14.img,if=none,id=drive-virtio-disk0 \
-device 
virtio-blk-pci,event_idx=on,scsi=off,bus=pci.0,addr=0x4,drive=drive-virtio-disk0,id=virtio-disk0 
\
</...>

This is the properties the QEMU device "scsi-disk" supports:

% ./x86_64-softmmu/qemu-system-x86_64 -device scsi-disk,?
scsi-disk.drive=drive
scsi-disk.logical_block_size=blocksize
scsi-disk.physical_block_size=blocksize
scsi-disk.min_io_size=uint16
scsi-disk.opt_io_size=uint32
scsi-disk.bootindex=int32
scsi-disk.discard_granularity=uint32
scsi-disk.ver=string
scsi-disk.serial=string
scsi-disk.vendor=string
scsi-disk.product=string
scsi-disk.removable=on/off
scsi-disk.dpofua=on/off
scsi-disk.wwn=hex64
scsi-disk.channel=uint32
scsi-disk.scsi-id=uint32
scsi-disk.lun=uint32

And the properties "virtio-blk-pci" device supports:

% ./x86_64-softmmu/qemu-system-x86_64 -device virtio-blk-pci,?
virtio-blk-pci.class=hex32
virtio-blk-pci.ioeventfd=on/off
virtio-blk-pci.vectors=uint32
virtio-blk-pci.indirect_desc=on/off
virtio-blk-pci.event_idx=on/off
virtio-blk-pci.drive=drive
virtio-blk-pci.logical_block_size=blocksize
virtio-blk-pci.physical_block_size=blocksize
virtio-blk-pci.min_io_size=uint16
virtio-blk-pci.opt_io_size=uint32
virtio-blk-pci.bootindex=int32
virtio-blk-pci.discard_granularity=uint32
virtio-blk-pci.cyls=uint32
virtio-blk-pci.heads=uint32
virtio-blk-pci.secs=uint32
virtio-blk-pci.serial=string
virtio-blk-pci.config-wce=on/off
virtio-blk-pci.scsi=on/off
virtio-blk-pci.addr=pci-devfn
virtio-blk-pci.romfile=string
virtio-blk-pci.rombar=uint32
virtio-blk-pci.multifunction=on/off
virtio-blk-pci.command_serr_enable=on/off

And the properties "virtio-scsi-pci" device supports:

% ./x86_64-softmmu/qemu-system-x86_64 -device virtio-scsi-pci,?
virtio-scsi-pci.ioeventfd=on/off
virtio-scsi-pci.vectors=uint32
virtio-scsi-pci.indirect_desc=on/off
virtio-scsi-pci.event_idx=on/off
virtio-scsi-pci.hotplug=on/off
virtio-scsi-pci.param_change=on/off
virtio-scsi-pci.num_queues=uint32
virtio-scsi-pci.max_sectors=uint32
virtio-scsi-pci.cmd_per_lun=uint32
virtio-scsi-pci.addr=pci-devfn
virtio-scsi-pci.romfile=string
virtio-scsi-pci.rombar=uint32
virtio-scsi-pci.multifunction=on/off
virtio-scsi-pci.command_serr_enable=on/off

We can put things like "ioeventfd", "event_idx" in the <driver> 
subelement, is
because of the QEMU device used for disk supports it. But for a 
virtio-scsi disk,
"num_queues" is supported in a separate device "virtio-scsi-pci" 
instead.. That
means, from libvirt p.o.v,  things like "ioevent_idx" are for disk, 
"num_queues"
is for the disk controller.

Assuming that we put "num_queues" or "numQueues" in <driver>, then we need
to find out the controller for disk when building QEMU command line, and 
check
if it's virtio-scsi model, if not, error out, otherwise tell the 
function to build the
controller device string that "num_queues" is specified, and what its 
value is. Or
something similar but reversely (find out the disk associated with the 
virtio-scsi
controller, check if num_queues is specified). This might be not the 
exact process,
but it can show putting "num_queues" in <driver> is just a straight 
wrong way to go...

Osier




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