[PATCH REBASE 5/7] qemu: Introduce QEMU_CAPS_MACHINE_MEMORY_BACKEND

[Michal Privoznik]

On 9/8/20 1:21 PM, Ján Tomko wrote:
> On a Tuesday in 2020, Michal Privoznik wrote:
>> This capability corresponds to '-machine memory-backend=' command
>> line argument. Unfortunately, it is not possible for us to detect
>> the capability via QMP and therefore we have to have a version
>> check.
> 
>> The QEMU capability was introduced in v5.1.0-3-gc556600598.
>>
> 
> Please rephrase this or drop the period at the end, e.g.:
> 
> QEMU commit v5.1.0-3-gc556600598 introduced the capability.
> 
> (to make it easier to select)
> 
>> Signed-off-by: Michal Privoznik <mprivozn at redhat.com>
>> ---
>> src/qemu/qemu_capabilities.c                     | 7 +++++++
>> src/qemu/qemu_capabilities.h                     | 3 +++
>> tests/qemucapabilitiesdata/caps_5.2.0.x86_64.xml | 1 +
>> 3 files changed, 11 insertions(+)
>>
>> diff --git a/src/qemu/qemu_capabilities.c b/src/qemu/qemu_capabilities.c
>> index dcfd7cdd4e..d0a7c7b30e 100644
>> --- a/src/qemu/qemu_capabilities.c
>> +++ b/src/qemu/qemu_capabilities.c
>> @@ -597,6 +597,9 @@ VIR_ENUM_IMPL(virQEMUCaps,
>>               "spapr-tpm-proxy",
>>               "numa.hmat",
>>               "blockdev-hostdev-scsi",
>> +
>> +              /* 380 */
>> +              "machine.memory-backend",
>>     );
>>
>>
>> @@ -5104,6 +5107,10 @@ virQEMUCapsInitQMPVersionCaps(virQEMUCapsPtr 
>> qemuCaps)
>>     /* TCG couldn't be disabled nor queried until QEMU 2.10 */
>>     if (qemuCaps->version < 2010000)
>>         virQEMUCapsSet(qemuCaps, QEMU_CAPS_TCG);
>> +
>> +    /* no way to query for -machine memory-backend */
>> +    if (qemuCaps->version >= 5001050)
> 
> That's a git version.
> 
> Also, the above mentioned commit introduces the 'default-ram-id'
> property, which does show up in our capability replies file.
> 
> Can't we safely assume that its presence also means that -machine
> memory-backend is supported?

Good point. We can do that. However, I will need to do a slight change 
to 6/7 to qemuTestCapsCacheInsert() because there I'm filling 
default-ram-id for all qemuCaps, even old versions that don't have it in 
real world. So basically, I will need to move this version check into 
qemuTestCapsCacheInsert() but I guess that's okay if I put a comment 
next to it.

Michal