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

[Kevin Wolf <kwolf@redhat.com>]

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 <pbonzini@redhat.com>
>   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 <pbonzini@redhat.com>
>       Signed-off-by: Kevin Wolf <kwolf@redhat.com>
> 
> Anthony Liguori <aliguori@us.ibm.com> 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 <aliguori@us.ibm.com>
> Signed-off-by: Stefan Hajnoczi <stefanha@linux.vnet.ibm.com>
> ---
> Anthony, does this fix your test case?

Looks good to me, but I think I'll wait for Anthony to check it.

Kevin