Re: [PATCH] qemu: define and use VIRTIO_PFN_SHIFT

[Hollis Blanchard <hollisb@us.ibm.com>]

On Thu, 2008-11-06 at 08:01 -0600, Anthony Liguori wrote:
> Hollis Blanchard wrote:
> > # HG changeset patch
> > # User Hollis Blanchard <hollisb@us.ibm.com>
> > # Date 1225946837 21600
> > # Node ID 43a111ea61b542d3823e2a11d017e7b06b7ec254
> > # Parent  b63967268af119e0faa4adc3086cdef857815548
> > qemu: define and use VIRTIO_PFN_SHIFT
> >
> > The virtio front and back ends must agree about how big a pfn really
> is. Since
> > qemu has no idea what "page size" the guest may be using, it must be
> > independent of TARGET_PAGE_BITS.
> >
> > This patch should have no functional effect on x86 or ia64, but I'd
> like an ack from the
> > ia64 guys.
> >   
> 
> Would be better to add a new header in target-XXX instead of using 
> cpu.h.  Virtio is not part of the CPU ISA.

OK.

> > Signed-off-by: Hollis Blanchard <hollisb@us.ibm.com>
> >
> > diff --git a/qemu/hw/virtio.c b/qemu/hw/virtio.c
> > --- a/qemu/hw/virtio.c
> > +++ b/qemu/hw/virtio.c
> > @@ -56,6 +56,10 @@
> >   */
> >  #define wmb() do { } while (0)
> >  
> > +#define VRING_PAGE_SIZE (1<<12)
> > +
> > +#define ALIGN(x, a)  (((x)+(a)-1) & ~((a)-1))
> > +
> >  /* virt queue functions */
> 
> Why is VRING_PAGE_SIZE not architecture specific?

I wanted to make sure people on non-x86 architectures couldn't run into
vring-size related problems that didn't also appear on x86.

-- 
Hollis Blanchard
IBM Linux Technology Center