clippy: Address the issue 'needless-borrow'

Issue from beta verion of clippy:

Error:    --> vm-virtio/src/queue.rs:700:59
    |
700 |             if let Some(used_event) = self.get_used_event(&mem) {
    |                                                           ^^^^ help: change this to: `mem`
    |
    = note: `-D clippy::needless-borrow` implied by `-D warnings`
    = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#needless_borrow

Signed-off-by: Bo Chen <chen.bo@intel.com>

net_util/src/ctrl_queue.rs

@@ -47,7 +47,7 @@ impl CtrlQueue {
 
     pub fn process(&mut self, mem: &GuestMemoryMmap, queue: &mut Queue) -> Result<bool> {
         let mut used_desc_heads = Vec::new();
-        for avail_desc in queue.iter(&mem) {
+        for avail_desc in queue.iter(mem) {
             let ctrl_hdr: ControlHeader =
                 mem.read_obj(avail_desc.addr).map_err(Error::GuestMemory)?;
             let data_desc = avail_desc
@@ -111,8 +111,8 @@ impl CtrlQueue {
         }
 
         for (desc_index, len) in used_desc_heads.iter() {
-            queue.add_used(&mem, *desc_index, *len);
-            queue.update_avail_event(&mem);
+            queue.add_used(mem, *desc_index, *len);
+            queue.update_avail_event(mem);
         }
 
         Ok(!used_desc_heads.is_empty())

net_util/src/mac.rs

@@ -57,7 +57,7 @@ impl MacAddr {
         // TODO: using something like std::mem::uninitialized could avoid the extra initialization,
         // if this ever becomes a performance bottleneck.
         let mut bytes = [0u8; MAC_ADDR_LEN];
-        bytes[..].copy_from_slice(&src);
+        bytes[..].copy_from_slice(src);
 
         MacAddr { bytes }
     }

net_util/src/queue_pair.rs

@@ -40,7 +40,7 @@ impl TxVirtio {
         queue: &mut Queue,
         rate_limiter: &mut Option<RateLimiter>,
     ) -> Result<(), NetQueuePairError> {
-        while let Some(avail_desc) = queue.iter(&mem).next() {
+        while let Some(avail_desc) = queue.iter(mem).next() {
             let head_index = avail_desc.index;
             let mut next_desc = Some(avail_desc);
 
@@ -108,8 +108,8 @@ impl TxVirtio {
                 self.counter_frames += Wrapping(1);
             }
 
-            queue.add_used(&mem, head_index, 0);
-            queue.update_avail_event(&mem);
+            queue.add_used(mem, head_index, 0);
+            queue.update_avail_event(mem);
         }
 
         Ok(())
@@ -146,7 +146,7 @@ impl RxVirtio {
         let mut exhausted_descs = true;
         let mut rate_limit_reached = false;
 
-        while let Some(avail_desc) = queue.iter(&mem).next() {
+        while let Some(avail_desc) = queue.iter(mem).next() {
             if rate_limit_reached {
                 exhausted_descs = false;
                 queue.go_to_previous_position();
@@ -208,8 +208,8 @@ impl RxVirtio {
                 0
             };
 
-            queue.add_used(&mem, head_index, len);
-            queue.update_avail_event(&mem);
+            queue.add_used(mem, head_index, len);
+            queue.update_avail_event(mem);
 
             // For the sake of simplicity (keeping the handling of RX_QUEUE_EVENT and
             // RX_TAP_EVENT totally asynchronous), we always let the 'last' descriptor

net_util/src/tap.rs

@@ -384,7 +384,7 @@ impl Read for Tap {
 
 impl Write for Tap {
     fn write(&mut self, buf: &[u8]) -> IoResult<usize> {
-        self.tap_file.write(&buf)
+        self.tap_file.write(buf)
     }
 
     fn flush(&mut self) -> IoResult<()> {