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

["Tan, Jianfeng" <jianfeng.tan@intel.com>]

> -----Original Message-----
> From: Yuanhan Liu [mailto:yuanhan.liu@linux.intel.com]
> Sent: Friday, April 14, 2017 1:32 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 Thu, Apr 13, 2017 at 02:12:56PM +0000, Jianfeng Tan wrote:
> > virtio-user cannot work on 32-bit system as higher 32-bit of the
> > addr field (64-bit) in the desc is filled with non-zero value
> > which should not happen for a 32-bit system.
> >
> > This is a regression bug. For 32-bit system, the first 4 bytes
> > is the virtual address, with following 8 bytes pointing to
> > physical addr.
> 
> It took me a while to understand that you were trying to say "the first
> 4 bytes __of mbuf__ is ...".

Oops, yes, missed that.

> 
> > With below wrong definition, both virtual address
> > and lower 4 bytes of physical addr are obtained.
> 
> Again, it's not complete. Something like "in the case of virtio-user,
> buf_addr will be used for filling the desc addr, ...". will make it much
> easier to understand.

Yes.

> 
> 
> >   #define VIRTIO_MBUF_ADDR(mb, vq) \
> > 	(*(uint64_t *)((uintptr_t)(mb) + (vq)->offset))
> >
> > Fixes: 25f80d108780 ("net/virtio: fix packet corruption")
> > Cc: stable@dpdk.org
> >
> > Signed-off-by: Jianfeng Tan <jianfeng.tan@intel.com>
> > ---
> >  drivers/net/virtio/virtqueue.h | 3 ++-
> >  1 file changed, 2 insertions(+), 1 deletion(-)
> >
> > 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. I usually use uintptr_t only for converter from pointer to integer, not the opposite way.

> 
>     (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