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Re: [Qemu-devel] [PATCH RFC] virtio-pci: fix LE host/BE guest capacity f
From: |
Michael S. Tsirkin |
Subject: |
Re: [Qemu-devel] [PATCH RFC] virtio-pci: fix LE host/BE guest capacity for blk |
Date: |
Tue, 28 May 2013 13:38:48 +0300 |
On Tue, May 28, 2013 at 12:14:59PM +0200, Paolo Bonzini wrote:
> 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
Yes, v2 I just sent fixes this.
Thanks for paying attention.
> > + 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);
> >