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Re: [Qemu-devel] [PATCH 4/4] virtio-blk: hide VIRTIO_BLK_F_CONFIG_WCE fr
From: |
Paolo Bonzini |
Subject: |
Re: [Qemu-devel] [PATCH 4/4] virtio-blk: hide VIRTIO_BLK_F_CONFIG_WCE from old machine types |
Date: |
Mon, 20 Aug 2012 14:46:09 +0200 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:14.0) Gecko/20120717 Thunderbird/14.0 |
Il 17/08/2012 21:25, Kevin Wolf ha scritto:
> From: Stefan Hajnoczi <address@hidden>
>
> 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>
> Signed-off-by: Kevin Wolf <address@hidden>
> ---
> hw/pc_piix.c | 4 ++++
> hw/virtio-blk.c | 4 +++-
> hw/virtio-blk.h | 1 +
> hw/virtio-pci.c | 1 +
> 4 files changed, 9 insertions(+), 1 deletions(-)
>
> diff --git a/hw/pc_piix.c b/hw/pc_piix.c
> index 0c0096f..d68dbb2 100644
> --- a/hw/pc_piix.c
> +++ b/hw/pc_piix.c
> @@ -375,6 +375,10 @@ static QEMUMachine pc_machine_v1_2 = {
> .driver = "qxl",\
> .property = "vgamem_mb",\
> .value = stringify(8),\
> + },{\
> + .driver = "virtio-blk-pci",\
> + .property = "config-wce",\
> + .value = "off",\
> }
>
> static QEMUMachine pc_machine_v1_1 = {
> diff --git a/hw/virtio-blk.c b/hw/virtio-blk.c
> index fd8fa90..0bc2b5e 100644
> --- a/hw/virtio-blk.c
> +++ b/hw/virtio-blk.c
> @@ -533,7 +533,9 @@ static uint32_t virtio_blk_get_features(VirtIODevice
> *vdev, uint32_t features)
> features |= (1 << VIRTIO_BLK_F_BLK_SIZE);
> features |= (1 << VIRTIO_BLK_F_SCSI);
>
> - features |= (1 << VIRTIO_BLK_F_CONFIG_WCE);
> + if (s->blk->config_wce) {
> + features |= (1 << VIRTIO_BLK_F_CONFIG_WCE);
> + }
> if (bdrv_enable_write_cache(s->bs))
> features |= (1 << VIRTIO_BLK_F_WCE);
>
> diff --git a/hw/virtio-blk.h b/hw/virtio-blk.h
> index 35834cf..454f445 100644
> --- a/hw/virtio-blk.h
> +++ b/hw/virtio-blk.h
> @@ -104,6 +104,7 @@ struct VirtIOBlkConf
> BlockConf conf;
> char *serial;
> uint32_t scsi;
> + uint32_t config_wce;
> };
>
> #define DEFINE_VIRTIO_BLK_FEATURES(_state, _field) \
> diff --git a/hw/virtio-pci.c b/hw/virtio-pci.c
> index 5e6e09e..2a3d86f 100644
> --- a/hw/virtio-pci.c
> +++ b/hw/virtio-pci.c
> @@ -886,6 +886,7 @@ static Property virtio_blk_properties[] = {
> #ifdef __linux__
> DEFINE_PROP_BIT("scsi", VirtIOPCIProxy, blk.scsi, 0, true),
> #endif
> + DEFINE_PROP_BIT("config-wce", VirtIOPCIProxy, blk.config_wce, 0, true),
> DEFINE_PROP_BIT("ioeventfd", VirtIOPCIProxy, flags,
> VIRTIO_PCI_FLAG_USE_IOEVENTFD_BIT, true),
> DEFINE_PROP_UINT32("vectors", VirtIOPCIProxy, nvectors, 2),
> DEFINE_VIRTIO_BLK_FEATURES(VirtIOPCIProxy, host_features),
>
Could/should this be added to DEFINE_VIRTIO_BLK_FEATURES instead? You
don't need the new field, and virtio_blk_get_features can simply omit
VIRTIO_BLK_F_CONFIG_WCE. At least that's how virtio-net does it.
It can be done in 1.3 though.
Paolo