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SubjectRe: [PATCH v4 26/42] vhost/net: force len for TX to host endian
On Tue, 25 Nov 2014 18:43:14 +0200
"Michael S. Tsirkin" <mst@redhat.com> wrote:

> We use native endian-ness internally but never
> expose it to guest.
>
> Signed-off-by: Michael S. Tsirkin <mst@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)

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?

>
> enum {
> VHOST_NET_FEATURES = VHOST_FEATURES |



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