virtio_vring_index里的guest_index和host_index分析

 

virtio_vring_index. 获取 vring queue里的guest_index和host_index，初步看是不清楚 什么是 guest_index和host_index。

void virtio_vring_index(VirtQueue *vq, NetVringIndex *index)

{

    index->guest_index = vring_get_used_event(vq);

    index->host_index = vring_used_idx(vq);

}

 

gues_index 通过 vring_get_used_event 获取，通过以下代码可以看出，其实就是取的 avail_index的值

/* Called within rcu_read_lock().  */
static inline uint16_t vring_avail_ring(VirtQueue *vq, int i)
{
    VRingMemoryRegionCaches *caches = vring_get_region_caches(vq);
    hwaddr pa = offsetof(VRingAvail, ring[i]);
    return virtio_lduw_phys_cached(vq->vdev, &caches->avail, pa);
}

/* Called within rcu_read_lock().  */
static inline uint16_t vring_get_used_event(VirtQueue *vq)
{
    return vring_avail_ring(vq, vq->vring.num);
}

host_index 通过vring_used_idx 获取，通过以下代码可以看出，其实就是取的 used_index的值

/* Called within rcu_read_lock().  */
static uint16_t vring_used_idx(VirtQueue *vq)
{
    VRingMemoryRegionCaches *caches = vring_get_region_caches(vq);
    hwaddr pa = offsetof(VRingUsed, idx);
    return virtio_lduw_phys_cached(vq->vdev, &caches->used, pa);
}