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

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

On Fri, Apr 14, 2017 at 06:56:01AM +0000, Tan, Jianfeng wrote:
> 
> 
> > -----Original Message-----
> > From: Yuanhan Liu [mailto:yuanhan.liu@linux.intel.com]
> > Sent: Friday, April 14, 2017 2:20 PM
> > To: Tan, Jianfeng
> > Cc: dev@dpdk.org; olivier.matz@6wind.com; stable@dpdk.org
> > Subject: Re: [PATCH] net/virtio-user: fix not working on 32-bit system
> > 
> > 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.
> 
> Another fold, if you refer to the definition of struct rte_mbuf, the first field is defined as void * instead of uintptr_t. I think that why I prefer to use ((void *)*) in the beginning.

But the type is hidden here: isn't this the purpose you were introducing
the "offset" here? Besides, it could be type "phys_addr_t".

	--yliu