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SubjectRe: [PATCH RFC 2/2] vhost: packed ring support
On Wed, Feb 14, 2018 at 10:37:09AM +0800, Jason Wang wrote:
[...]
> +static void set_desc_used(struct vhost_virtqueue *vq,
> + struct vring_desc_packed *desc, bool wrap_counter)
> +{
> + __virtio16 flags = desc->flags;
> +
> + if (wrap_counter) {
> + desc->flags |= cpu_to_vhost16(vq, DESC_AVAIL);
> + desc->flags |= cpu_to_vhost16(vq, DESC_USED);
> + } else {
> + desc->flags &= ~cpu_to_vhost16(vq, DESC_AVAIL);
> + desc->flags &= ~cpu_to_vhost16(vq, DESC_USED);
> + }
> +
> + desc->flags = flags;

The `desc->flags` is restored after the change.

> +}
> +
> +static int vhost_get_vq_desc_packed(struct vhost_virtqueue *vq,
> + struct iovec iov[], unsigned int iov_size,
> + unsigned int *out_num, unsigned int *in_num,
> + struct vhost_log *log,
> + unsigned int *log_num)
> +{
> + struct vring_desc_packed desc;
> + int ret, access, i;
> + u16 avail_idx = vq->last_avail_idx;
> +
> + /* When we start there are none of either input nor output. */
> + *out_num = *in_num = 0;
> + if (unlikely(log))
> + *log_num = 0;
> +
> + do {
> + unsigned int iov_count = *in_num + *out_num;
> +
> + i = vq->last_avail_idx & (vq->num - 1);

The queue size may not be a power of 2 in packed ring.

Best regards,
Tiwei Bie

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