On Wed, Nov 26, 2014 at 03:31:02PM +0100, Cornelia Huck wrote:
> On Tue, 25 Nov 2014 18:43:14 +0200
> "Michael S. Tsirkin" <mst@xxxxxxxxxx> wrote:
>
> > We use native endian-ness internally but never
> > expose it to guest.
> >
> > Signed-off-by: Michael S. Tsirkin <mst@xxxxxxxxxx>
> > ---
> > 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)
>
> I find these constants a bit confusing: What does __virtio32 mean
> without the context of a vq or device?
>
> >
> > -#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)
>
> And here you cast it to a plain u32 again.
>
> I looked at the final code, and you seem either to use the above
> constants for .len or do a cpu_to_vhost32(). Wouldn't you need to
> convert the constants as well?
I tried to explain it in the commit message.
It's a hack in vhost: it keeps virtio used structure in host
memory, but abuses length field for internal housekeeping.
This works because length in used ring for tx is always 0.
> >
> > enum {
> > VHOST_NET_FEATURES = VHOST_FEATURES |
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