Re: [Qemu-devel] [PATCH RFC] virtio-pci: fix LE host/BE guest capacity for blk

[Paolo Bonzini]

Il 28/05/2013 12:11, Michael S. Tsirkin ha scritto:
> When a BE guest reads capacity from an LE host virtio-blk device or vice
> versa, it will get the dwords of the qword field swapped.
> As virtio-blk is the only one with such a quirk,
> and as non-pci transports don't do byte-swaps at all,
> solve this with a bit of device-specific hackery in
> virtio-pci.
> 
> Signed-off-by: Michael S. Tsirkin <address@hidden>
> ---
> 
> I don't seem to be able to boot any big-endian
> guests ATM, so this is only compile-tested - sending
> this out for early feedback/flames.
> Testing reports also wellcome!
> 
>  hw/virtio/virtio-pci.c | 9 +++++++++
>  1 file changed, 9 insertions(+)
> 
> diff --git a/hw/virtio/virtio-pci.c b/hw/virtio/virtio-pci.c
> index 9668b2b..0e9ae4c 100644
> --- a/hw/virtio/virtio-pci.c
> +++ b/hw/virtio/virtio-pci.c
> @@ -411,6 +411,15 @@ static uint64_t virtio_pci_config_read(void *opaque, 
> hwaddr addr,
>          }
>          break;
>      case 4:
> +        /* Most devices don't have 64 bit config fields.
> +         * Block is an exception: first 8 bytes include
> +         * a 64 bit capacity field.
> +         */
> +        if (virtio_is_big_endian() != defined(HOST_WORDS_BIGENDIAN) &&

I thought think this is not valid C?

Paolo

> +            proxy->vdev->dev_id == VIRTIO_ID_BLOCK && addr < 8) {
> +            /* Swap first two words */
> +            addr ^= 0x4;
> +        }
>          val = virtio_config_readl(proxy->vdev, addr);
>          if (virtio_is_big_endian()) {
>              val = bswap32(val);
>