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Re: [Qemu-devel] [PATCH for-1.2] virtio-blk: hide VIRTIO_BLK_F_CONFIG_WC
From: |
Kevin Wolf |
Subject: |
Re: [Qemu-devel] [PATCH for-1.2] virtio-blk: hide VIRTIO_BLK_F_CONFIG_WCE from old machine types |
Date: |
Thu, 16 Aug 2012 11:07:39 +0200 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:13.0) Gecko/20120605 Thunderbird/13.0 |
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.
Kevin