Re: [Qemu-devel] [PATCH for-1.2] virtio-blk: hide VIRTIO_BLK_F_CONFIG_WCE from old machine types

[Stefan Hajnoczi]

On Thu, Aug 16, 2012 at 10:07 AM, Kevin Wolf <address@hidden> wrote:
> Am 16.08.2012 10:57, schrieb Stefan Hajnoczi:
>> QEMU has a policy of keeping a stable guest device ABI.  When new guest 
>> device
>> features are introduced they must not change hardware info seen by existing
>> guests.  This is important because operating systems or applications may
>> "fingerprint" the hardware and refuse to run when the hardware changes.  To
>> always get the latest guest device ABI, run with x86 machine type "pc".
>>
>> This patch hides the new VIRTIO_BLK_F_CONFIG_WCE virtio feature bit from
>> existing machine types.  Only pc-1.2 and later will expose this feature
>> by default.
>>
>> For more info on the VIRTIO_BLK_F_CONFIG_WCE feature bit, see:
>>
>>   commit 13e3dce068773c971ff2f19d986378c55897c4a3
>>   Author: Paolo Bonzini <address@hidden>
>>   Date:   Thu Aug 9 16:07:19 2012 +0200
>>
>>       virtio-blk: support VIRTIO_BLK_F_CONFIG_WCE
>>
>>       Also rename VIRTIO_BLK_F_WCACHE to VIRTIO_BLK_F_WCE for consistency 
>> with
>>       the spec.
>>
>>       Signed-off-by: Paolo Bonzini <address@hidden>
>>       Signed-off-by: Kevin Wolf <address@hidden>
>>
>> Anthony Liguori <address@hidden> reported:
>>
>>   This broke qemu-test because it changed the pc-1.0 machine type:
>>
>>   Setting guest RANDOM seed to 47167
>>   *** Running tests ***
>>   Running test /tests/finger-print.sh...              OK
>>   --- fingerprints/pc-1.0.x86_64      2011-12-18 13:08:40.000000000 -0600
>>   +++ fingerprint.txt 2012-08-12 13:30:48.000000000 -0500
>>   @@ -55,7 +55,7 @@
>>    /sys/bus/pci/devices/0000:00:06.0/subsystem_device=0x0002
>>    /sys/bus/pci/devices/0000:00:06.0/class=0x010000
>>    /sys/bus/pci/devices/0000:00:06.0/revision=0x00
>>   -/sys/bus/pci/devices/0000:00:06.0/virtio/host-features=0x710006d4
>>   +/sys/bus/pci/devices/0000:00:06.0/virtio/host-features=0x71000ed4
>>    /sys/class/dmi/id/bios_vendor=Bochs
>>    /sys/class/dmi/id/bios_date=01/01/2007
>>    /sys/class/dmi/id/bios_version=Bochs
>>   Guest fingerprint changed for pc-1.0!
>>
>> Reported-by: Anthony Liguori <address@hidden>
>> Signed-off-by: Stefan Hajnoczi <address@hidden>
>> ---
>> Anthony, does this fix your test case?
>
> Looks good to me, but I think I'll wait for Anthony to check it.

Yep, we definitely need to check because I haven't run qemu-test myself.

Stefan