Re: [Qemu-devel] [libvirt] [PATCH 3/5] qemu: add QEMU_CAPS_MACHINE_VMPORT_OPT

[Martin Kletzander <mkletzan@redhat.com>]

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On Tue, Apr 14, 2015 at 10:07:00AM -0600, Eric Blake wrote:
>[adding qemu]
>
>On 04/14/2015 09:58 AM, Marc-André Lureau wrote:
>> Hi
>>
>> On Tue, Apr 14, 2015 at 4:25 PM, Martin Kletzander <mkletzan@redhat.com>
>> wrote:
>>
>>> Is this not exposed in any way in QEMU?  Do we really need to use this
>>> (what we're trying to avoid)?
>>>
>>
>> That works with the following change:
>>
>> diff --git a/src/qemu/qemu_capabilities.c b/src/qemu/qemu_capabilities.c
>> index 768cef1..1b20a7f 100644
>> --- a/src/qemu/qemu_capabilities.c
>> +++ b/src/qemu/qemu_capabilities.c
>> @@ -2510,6 +2510,7 @@ struct virQEMUCapsCommandLineProps {
>>
>>  static struct virQEMUCapsCommandLineProps virQEMUCapsCommandLine[] = {
>>      { "machine", "mem-merge", QEMU_CAPS_MEM_MERGE },
>> +    { "machine", "vmport", QEMU_CAPS_MACHINE_VMPORT_OPT },
>
>Ouch.  qemu commit 0a7cf21 fixes what would have been a regression in
>2.3 at exposing "mem-merge" through query-command-line-options, but it
>does NOT expose "vmport", which is a per-architecture option rather than
>a generic -machine option.  Which means that even though qemu 2.2
>(perhaps wrongly) advertised "vmport" for all machines (even when it was
>not supported), 2.3 will not advertise it, and we are hoping for a
>better solution in 2.4 for properly advertising vmport on an
>as-appropriate basis.
>
>Yes, we WANT to use QMP probing,...
>
>>      { "drive", "discard", QEMU_CAPS_DRIVE_DISCARD },
>>      { "realtime", "mlock", QEMU_CAPS_MLOCK },
>>      { "boot-opts", "strict", QEMU_CAPS_BOOT_STRICT },
>> @@ -3243,10 +3244,6 @@ virQEMUCapsInitQMPMonitor(virQEMUCapsPtr qemuCaps,
>>      if (qemuCaps->version >= 1003000)
>>          virQEMUCapsSet(qemuCaps, QEMU_CAPS_MACHINE_USB_OPT);
>>
>> -    /* vmport option is supported v2.2.0 onwards */
>> -    if (qemuCaps->version >= 2002000)
>> -        virQEMUCapsSet(qemuCaps, QEMU_CAPS_MACHINE_VMPORT_OPT);
>
>...and not version comparison, but we'll need something better in QMP
>for 2.3 (which is rather late, since we missed 2.3-rc3) if you can't
>come up with anything better for learning whether vmport is supported.
>

Ouch, I missed that.  But that's something we need for more than just
vmport attribute, but also all other machine-specific ones :(

I still think this might go in, though.

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