devices: Add support for i8042 reset device

Introduce emulation of i8042 device to allow the guest to stop the
VM by issuing a reset event.

The device has been copied over from the Crosvm code base, relying on
the commit 0268e26e1ac9e09aa51d733482c5df139cd8d588.

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

devices/src/legacy/i8042.rs

@@ -0,0 +1,42 @@
+// Copyright 2017 The Chromium OS Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+use vmm_sys_util::EventFd;
+
+use BusDevice;
+
+/// A i8042 PS/2 controller that emulates just enough to shutdown the machine.
+pub struct I8042Device {
+    reset_evt: EventFd,
+}
+
+impl I8042Device {
+    /// Constructs a i8042 device that will signal the given event when the guest requests it.
+    pub fn new(reset_evt: EventFd) -> I8042Device {
+        I8042Device { reset_evt }
+    }
+}
+
+// i8042 device is located at I/O port 0x61. We partially implement two 8-bit
+// registers: port 0x61 (I8042_PORT_B_REG, offset 0 from base of 0x61), and
+// port 0x64 (I8042_COMMAND_REG, offset 3 from base of 0x61).
+impl BusDevice for I8042Device {
+    fn read(&mut self, offset: u64, data: &mut [u8]) {
+        if data.len() == 1 && offset == 3 {
+            data[0] = 0x0;
+        } else if data.len() == 1 && offset == 0 {
+            // Like kvmtool, we return bit 5 set in I8042_PORT_B_REG to
+            // avoid hang in pit_calibrate_tsc() in Linux kernel.
+            data[0] = 0x20;
+        }
+    }
+
+    fn write(&mut self, offset: u64, data: &[u8]) {
+        if data.len() == 1 && data[0] == 0xfe && offset == 3 {
+            if let Err(e) = self.reset_evt.write(1) {
+                println!("Error triggering i8042 reset event: {}", e);
+            }
+        }
+    }
+}

devices/src/legacy/mod.rs

@@ -6,5 +6,7 @@
 // found in the THIRD-PARTY file.
 
 mod serial;
+mod i8042;
 
 pub use self::serial::Serial;
+pub use self::i8042::I8042Device;