Re: [PATCH] net/virtio-user: fix not working on 32-bit system

[Yuanhan Liu <yuanhan.liu@linux.intel.com>]

On Fri, Apr 14, 2017 at 05:53:55AM +0000, Tan, Jianfeng wrote:
> > > diff --git a/drivers/net/virtio/virtqueue.h b/drivers/net/virtio/virtqueue.h
> > > index f9e3736..f43ea70 100644
> > > --- a/drivers/net/virtio/virtqueue.h
> > > +++ b/drivers/net/virtio/virtqueue.h
> > > @@ -72,7 +72,8 @@ struct rte_mbuf;
> > >   * Return the physical address (or virtual address in case of
> > >   * virtio-user) of mbuf data buffer.
> > >   */
> > > -#define VIRTIO_MBUF_ADDR(mb, vq) (*(uint64_t *)((uintptr_t)(mb) +
> > (vq)->offset))
> > > +#define VIRTIO_MBUF_ADDR(mb, vq) \
> > > +	((uint64_t)((uintptr_t)(*(void **)((uintptr_t)(mb) + (vq)->offset))))
> > 
> > The "void **" cast makes it a bit complex (thus hard to read). I think
> > following should work?
> 
> Yes, uintptr_t can work. I thought void ** is easier to understand, meaning a convert to a pointer which pointing to a pointer.

It's twisted, isn't it? :)

> I usually use uintptr_t only for converter from pointer to integer, not the opposite way.

Yes, that's a typical usage. But the fact of the matter is uintptr_t
represents the word size, which is exactly what needed in this case.

	--yliu
> 
> > 
> >     (uint64_t(*(uintptr_t *)((uintptr_t)(mb) + (vq)->offset)))
> > 
> > Besides, it deserves a comment.
> 
> Will add comment in next version.
> 
> Thanks,
> Jianfeng
> 
> > 
> > 	--yliu
> > 
> > >  #else
> > >  #define VIRTIO_MBUF_ADDR(mb, vq) ((mb)->buf_physaddr)
> > >  #endif
> > > --
> > > 2.7.4