From 7a3e6caca4599390e318894ef7e4a13ced8189a8 Mon Sep 17 00:00:00 2001
From: Sebastien Boeuf <sebastien.boeuf@intel.com>
Date: Wed, 8 Jan 2020 11:55:30 +0100
Subject: [PATCH] vm-virtio: Simplify virtio-console input processing

The existing code was a bit too complex and it was introducing a bug
when trying to paste long lines directly to the console. By simplifying
the code, and by doing proper usage of the drain() function, the bug is
fixed by this commit.

Here is the similar output one could have gotten from time to time, when
pasting important amounts of bytes:

ERROR:vm-virtio/src/console.rs:104 -- Failed to write slice:
InvalidGuestAddress(GuestAddress(1040617472))

Signed-off-by: Sebastien Boeuf <sebastien.boeuf@intel.com>
---
 vm-virtio/src/console.rs | 31 +++++++++++--------------------
 1 file changed, 11 insertions(+), 20 deletions(-)

diff --git a/vm-virtio/src/console.rs b/vm-virtio/src/console.rs
index 994357044..b27e73e5e 100755
--- a/vm-virtio/src/console.rs
+++ b/vm-virtio/src/console.rs
@@ -79,37 +79,27 @@ impl ConsoleEpollHandler {
      */
     fn process_input_queue(&mut self) -> bool {
         let mut in_buffer = self.in_buffer.lock().unwrap();
-        let count = in_buffer.len();
         let recv_queue = &mut self.queues[0]; //receiveq
         let mut used_desc_heads = [(0, 0); QUEUE_SIZE as usize];
         let mut used_count = 0;
-        let mut write_count = 0;
+
+        if in_buffer.is_empty() {
+            return false;
+        }
 
         let mem = self.mem.load();
         for avail_desc in recv_queue.iter(&mem) {
-            let len;
-
-            let limit = cmp::min(write_count + avail_desc.len as u32, count as u32);
-            let source_slice = in_buffer
-                .drain(write_count as usize..limit as usize)
-                .collect::<Vec<u8>>();
-            let write_result = mem.write_slice(&source_slice[..], avail_desc.addr);
-
-            match write_result {
-                Ok(_) => {
-                    len = limit - write_count; //avail_desc.len;
-                    write_count = limit;
-                }
-                Err(e) => {
-                    error!("Failed to write slice: {:?}", e);
-                    break;
-                }
+            let len = cmp::min(avail_desc.len as u32, in_buffer.len() as u32);
+            let source_slice = in_buffer.drain(..len as usize).collect::<Vec<u8>>();
+            if let Err(e) = mem.write_slice(&source_slice[..], avail_desc.addr) {
+                error!("Failed to write slice: {:?}", e);
+                break;
             }
 
             used_desc_heads[used_count] = (avail_desc.index, len);
             used_count += 1;
 
-            if write_count >= count as u32 {
+            if in_buffer.is_empty() {
                 break;
             }
         }
@@ -117,6 +107,7 @@ impl ConsoleEpollHandler {
         for &(desc_index, len) in &used_desc_heads[..used_count] {
             recv_queue.add_used(&mem, desc_index, len);
         }
+
         used_count > 0
     }