virtio-devices: Improve queue handling with pop_descriptor_chain()

Using pop_descriptor_chain() is much more appropriate than iter() since
it recreates the iterator every time, avoiding the queue to be borrowed
and allowing the virtio-net implementation to match all the other ones.

Signed-off-by: Sebastien Boeuf <sebastien.boeuf@intel.com>

virtio-devices/src/rng.rs

@@ -22,7 +22,7 @@ use std::sync::atomic::AtomicBool;
 use std::sync::{Arc, Barrier};
 use versionize::{VersionMap, Versionize, VersionizeResult};
 use versionize_derive::Versionize;
-use virtio_queue::{Queue, QueueOwnedT, QueueT};
+use virtio_queue::{Queue, QueueT};
 use vm_memory::{Bytes, GuestAddressSpace, GuestMemoryAtomic};
 use vm_migration::VersionMapped;
 use vm_migration::{Migratable, MigratableError, Pausable, Snapshot, Snapshottable, Transportable};
@@ -52,7 +52,7 @@ impl RngEpollHandler {
 
         let mut used_desc_heads = [(0, 0); QUEUE_SIZE as usize];
         let mut used_count = 0;
-        for mut desc_chain in queue.iter(self.mem.memory()).unwrap() {
+        while let Some(mut desc_chain) = queue.pop_descriptor_chain(self.mem.memory()) {
             let desc = desc_chain.next().unwrap();
             let mut len = 0;