Re: [Qemu-devel] [PATCH v4 26/39] pcnet: convert to memory API

[Avi Kivity <avi@redhat.com>]

On 08/09/2011 03:42 PM, Michael S. Tsirkin wrote:
> On Tue, Aug 09, 2011 at 09:52:17AM +0300, Avi Kivity wrote:
> >  On 08/09/2011 09:55 AM, Bob Breuer wrote:
> >  >>    static void lance_cleanup(VLANClientState *nc)
> >  >>   @@ -117,13 +116,11 @@ static int lance_init(SysBusDevice *dev)
> >  >>        SysBusPCNetState *d = FROM_SYSBUS(SysBusPCNetState, dev);
> >  >>        PCNetState *s =&d->state;
> >  >>
> >  >>   -    s->mmio_index =
> >  >>   -        cpu_register_io_memory(lance_mem_read, lance_mem_write, d,
> >  >>   -                               DEVICE_NATIVE_ENDIAN);
> >  >>   +    memory_region_init_io(&s->mmio,&lance_mem_ops, s, "lance-mmio", 4);
> >  >
> >  >You've switched up d and s here, so anything that tries to talk to the
> >  >ethernet, such as a sparc32 guest, will now cause Qemu to segfault.
> >  >
> >  >
> >
> >  Good catch; will post a fix.
> >
> >  Maybe keeping the opaque wasn't such a good idea.
>
> Yes, we typically can get from the mmio to the device state
> using container_of.
>
>

But in some cases, we can't, and the it's a pain having to wrap 
MemoryRegion in another structure containing an opaque.

Maybe a good compromise is to:

   - keep MemoryRegion::opaque
   - pass a MemoryRegion *mr to callbacks instead of opaque
   - use container_of() when possible
   - use mr->opaque otherwise

-- 
error compiling committee.c: too many arguments to function