virtio: avoid redundant invocation of Queue::is_valid()

The lifecycle of VirtIO queue object is as below:
1) MMIO transport driver creates queues
2) MMIO transport validates all queues are valid by calling Queue::is_valid()
3) Passing queues to VirtDevice by calling VirtDevice::activate()
4) VirtDevice device driver creates iterator to access available descritpors
5) MMIO transport reset the VirtDevice by calling VirtDevice::reset()
6) MMIO transport changes/destroys queues

The MMIO transport driver won't touch those queues between stage 3 and stage 5,
so Queue::is_valid will always return true during stage 4. Get rid of the
redundant invocation of Queue::is_valid() in Queue::iter().

Signed-off-by: Liu Jiang <[email protected]>

Author: jiangliu

devices/src/virtio/queue.rs

@@ -322,9 +322,6 @@ impl Queue {
 
     /// A consuming iterator over all available descriptor chain heads offered by the driver.
     pub fn iter<'a, 'b>(&'b mut self, mem: &'a GuestMemory) -> AvailIter<'a, 'b> {
-        if !self.is_valid(mem) {
-            return AvailIter::new(mem, &mut self.next_avail);
-        }
         let queue_size = self.actual_size();
         let avail_ring = self.avail_ring;