Re: [PATCH v7 30/46] vhost/net: force len for TX to host endian

Michael S. Tsirkin
2014-12-01T12:33:54Z

On Mon, Dec 01, 2014 at 01:20:51PM +0100, Cornelia Huck wrote:
> On Sun, 30 Nov 2014 17:11:44 +0200
> "Michael S. Tsirkin" <mst@redhat.com> wrote:
>
> > vhost/net keeps a copy of some used ring but (ab)uses length
> > field for internal house-keeping. This works because
> > for tx used length is always 0.
> > Suppress sparse errors: we use native endian-ness internally but never
> > expose it to guest.
>
> I admit that I find this patch description hard to read :)
>
>
> "vhost/net keeps a copy of the used ring in host memory but (ab)uses
> the length field for internal house-keeping. This works because the
> length in the used ring for tx is always 0. In order to suppress sparse
> errors, we need to force native endianness."
>
> ?

Yes. Add to this "These values are never exposed to guest."

> >
> > Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
> > Reviewed-by: Jason Wang <jasowang@redhat.com>
> > ---
> > drivers/vhost/net.c | 10 +++++-----
> > 1 file changed, 5 insertions(+), 5 deletions(-)
> >
> > diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c
> > index 8dae2f7..dce5c58 100644
> > --- a/drivers/vhost/net.c
> > +++ b/drivers/vhost/net.c
> > @@ -48,15 +48,15 @@ MODULE_PARM_DESC(experimental_zcopytx, "Enable Zero Copy TX;"
> > * status internally; used for zerocopy tx only.
> > */
> > /* Lower device DMA failed */
> > -#define VHOST_DMA_FAILED_LEN 3
> > +#define VHOST_DMA_FAILED_LEN ((__force __virtio32)3)
> > /* Lower device DMA done */
> > -#define VHOST_DMA_DONE_LEN 2
> > +#define VHOST_DMA_DONE_LEN ((__force __virtio32)2)
> > /* Lower device DMA in progress */
> > -#define VHOST_DMA_IN_PROGRESS 1
> > +#define VHOST_DMA_IN_PROGRESS ((__force __virtio32)1)
> > /* Buffer unused */
> > -#define VHOST_DMA_CLEAR_LEN 0
> > +#define VHOST_DMA_CLEAR_LEN ((__force __virtio32)0)
> >
> > -#define VHOST_DMA_IS_DONE(len) ((len) >= VHOST_DMA_DONE_LEN)
> > +#define VHOST_DMA_IS_DONE(len) ((__force u32)(len) >= (__force u32)VHOST_DMA_DONE_LEN)
> >
> > enum {
> > VHOST_NET_FEATURES = VHOST_FEATURES |