cloud-hypervisor: Add devices crate

Based on the Firecracker devices crate from commit 9cdb5b2. It is a trimmed down version compared to the Firecracker one, to remove a bunch of pulled dependencies (logger, metrics, rate limiter, etc...). Signed-off-by: Samuel Ortiz <sameo@linux.intel.com>
2024-12-22 05:35:20 +00:00 · 2019-03-07 14:56:43 +01:00 · 2019-03-07 14:56:43 +01:00 · 1853b350ee
commit 1853b350ee
parent 7e2d1aca2d
10 changed files with 840 additions and 24 deletions
--- a/Cargo.lock
+++ b/Cargo.lock
@ -34,6 +34,11 @@ name = "bitflags"
 version = "0.9.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"

+[[package]]
+name = "bitflags"
+version = "1.0.4"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+
 [[package]]
 name = "byteorder"
 version = "1.2.1"
@ -61,6 +66,26 @@ dependencies = [
 "vmm 0.1.0",
 ]

+[[package]]
+name = "devices"
+version = "0.1.0"
+dependencies = [
+ "byteorder 1.2.1 (registry+https://github.com/rust-lang/crates.io-index)",
+ "epoll 4.0.1 (registry+https://github.com/rust-lang/crates.io-index)",
+ "libc 0.2.48 (registry+https://github.com/rust-lang/crates.io-index)",
+ "vm-memory 0.1.0 (git+https://github.com/rust-vmm/vm-memory)",
+ "vmm-sys-util 0.1.0 (git+https://github.com/sameo/vmm-sys-util)",
+]
+
+[[package]]
+name = "epoll"
+version = "4.0.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+dependencies = [
+ "bitflags 1.0.4 (registry+https://github.com/rust-lang/crates.io-index)",
+ "libc 0.2.48 (registry+https://github.com/rust-lang/crates.io-index)",
+]
+
 [[package]]
 name = "kvm-bindings"
 version = "0.1.1"
@ -147,6 +172,7 @@ name = "vmm"
 version = "0.1.0"
 dependencies = [
 "arch 0.1.0",
+ "devices 0.1.0",
 "kvm-bindings 0.1.1 (registry+https://github.com/rust-lang/crates.io-index)",
 "kvm-ioctls 0.1.0 (git+https://github.com/rust-vmm/kvm-ioctls)",
 "libc 0.2.48 (registry+https://github.com/rust-lang/crates.io-index)",
@ -186,8 +212,10 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 "checksum ansi_term 0.9.0 (registry+https://github.com/rust-lang/crates.io-index)" = "23ac7c30002a5accbf7e8987d0632fa6de155b7c3d39d0067317a391e00a2ef6"
 "checksum atty 0.2.11 (registry+https://github.com/rust-lang/crates.io-index)" = "9a7d5b8723950951411ee34d271d99dddcc2035a16ab25310ea2c8cfd4369652"
 "checksum bitflags 0.9.1 (registry+https://github.com/rust-lang/crates.io-index)" = "4efd02e230a02e18f92fc2735f44597385ed02ad8f831e7c1c1156ee5e1ab3a5"
+"checksum bitflags 1.0.4 (registry+https://github.com/rust-lang/crates.io-index)" = "228047a76f468627ca71776ecdebd732a3423081fcf5125585bcd7c49886ce12"
 "checksum byteorder 1.2.1 (registry+https://github.com/rust-lang/crates.io-index)" = "652805b7e73fada9d85e9a6682a4abd490cb52d96aeecc12e33a0de34dfd0d23"
 "checksum clap 2.27.1 (registry+https://github.com/rust-lang/crates.io-index)" = "1b8c532887f1a292d17de05ae858a8fe50a301e196f9ef0ddb7ccd0d1d00f180"
+"checksum epoll 4.0.1 (registry+https://github.com/rust-lang/crates.io-index)" = "f3f0680f2a6f2a17fa7a8668a27c54e45e1ad1cf8a632f56a7c19b9e4e3bbe8a"
 "checksum kvm-bindings 0.1.1 (registry+https://github.com/rust-lang/crates.io-index)" = "c223e8703d2eb76d990c5f58e29c85b0f6f50e24b823babde927948e7c71fc03"
 "checksum kvm-ioctls 0.1.0 (git+https://github.com/rust-vmm/kvm-ioctls)" = "<none>"
 "checksum libc 0.2.48 (registry+https://github.com/rust-lang/crates.io-index)" = "e962c7641008ac010fa60a7dfdc1712449f29c44ef2d4702394aea943ee75047"
--- a/devices/Cargo.toml
+++ b/devices/Cargo.toml
@ -0,0 +1,14 @@
+[package]
+name = "devices"
+version = "0.1.0"
+authors = ["The Chromium OS Authors"]
+
+[dependencies]
+byteorder = ">=1.2.1"
+epoll = "=4.0.1"
+libc = ">=0.2.39"
+vm-memory = { git = "https://github.com/rust-vmm/vm-memory" }
+vmm-sys-util = { git = "https://github.com/sameo/vmm-sys-util" }
+
+[dev-dependencies]
+tempfile = ">=3.0.2"
--- a/devices/src/bus.rs
+++ b/devices/src/bus.rs
@ -0,0 +1,256 @@
+// Copyright 2018 Amazon.com, Inc. or its affiliates. All Rights Reserved.
+// SPDX-License-Identifier: Apache-2.0
+//
+// Portions 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 THIRD-PARTY file.
+
+//! Handles routing to devices in an address space.
+
+use std::cmp::{Ord, Ordering, PartialEq, PartialOrd};
+use std::collections::btree_map::BTreeMap;
+use std::result;
+use std::sync::{Arc, Mutex};
+
+/// Trait for devices that respond to reads or writes in an arbitrary address space.
+///
+/// The device does not care where it exists in address space as each method is only given an offset
+/// into its allocated portion of address space.
+#[allow(unused_variables)]
+pub trait BusDevice: Send {
+    /// Reads at `offset` from this device
+    fn read(&mut self, offset: u64, data: &mut [u8]) {}
+    /// Writes at `offset` into this device
+    fn write(&mut self, offset: u64, data: &[u8]) {}
+    /// Triggers the `irq_mask` interrupt on this device
+    fn interrupt(&self, irq_mask: u32) {}
+}
+
+#[derive(Debug)]
+pub enum Error {
+    /// The insertion failed because the new device overlapped with an old device.
+    Overlap,
+}
+
+pub type Result<T> = result::Result<T, Error>;
+
+#[derive(Debug, Copy, Clone)]
+struct BusRange(u64, u64);
+
+impl Eq for BusRange {}
+
+impl PartialEq for BusRange {
+    fn eq(&self, other: &BusRange) -> bool {
+        self.0 == other.0
+    }
+}
+
+impl Ord for BusRange {
+    fn cmp(&self, other: &BusRange) -> Ordering {
+        self.0.cmp(&other.0)
+    }
+}
+
+impl PartialOrd for BusRange {
+    fn partial_cmp(&self, other: &BusRange) -> Option<Ordering> {
+        self.0.partial_cmp(&other.0)
+    }
+}
+
+/// A device container for routing reads and writes over some address space.
+///
+/// This doesn't have any restrictions on what kind of device or address space this applies to. The
+/// only restriction is that no two devices can overlap in this address space.
+#[derive(Clone, Default)]
+pub struct Bus {
+    devices: BTreeMap<BusRange, Arc<Mutex<BusDevice>>>,
+}
+
+impl Bus {
+    /// Constructs an a bus with an empty address space.
+    pub fn new() -> Bus {
+        Bus {
+            devices: BTreeMap::new(),
+        }
+    }
+
+    fn first_before(&self, addr: u64) -> Option<(BusRange, &Mutex<BusDevice>)> {
+        // for when we switch to rustc 1.17: self.devices.range(..addr).iter().rev().next()
+        for (range, dev) in self.devices.iter().rev() {
+            if range.0 <= addr {
+                return Some((*range, dev));
+            }
+        }
+        None
+    }
+
+    pub fn get_device(&self, addr: u64) -> Option<(u64, &Mutex<BusDevice>)> {
+        if let Some((BusRange(start, len), dev)) = self.first_before(addr) {
+            let offset = addr - start;
+            if offset < len {
+                return Some((offset, dev));
+            }
+        }
+        None
+    }
+
+    /// Puts the given device at the given address space.
+    pub fn insert(&mut self, device: Arc<Mutex<BusDevice>>, base: u64, len: u64) -> Result<()> {
+        if len == 0 {
+            return Err(Error::Overlap);
+        }
+
+        // Reject all cases where the new device's base is within an old device's range.
+        if self.get_device(base).is_some() {
+            return Err(Error::Overlap);
+        }
+
+        // The above check will miss an overlap in which the new device's base address is before the
+        // range of another device. To catch that case, we search for a device with a range before
+        // the new device's range's end. If there is no existing device in that range that starts
+        // after the new device, then there will be no overlap.
+        if let Some((BusRange(start, _), _)) = self.first_before(base + len - 1) {
+            // Such a device only conflicts with the new device if it also starts after the new
+            // device because of our initial `get_device` check above.
+            if start >= base {
+                return Err(Error::Overlap);
+            }
+        }
+
+        if self.devices.insert(BusRange(base, len), device).is_some() {
+            return Err(Error::Overlap);
+        }
+
+        Ok(())
+    }
+
+    /// Reads data from the device that owns the range containing `addr` and puts it into `data`.
+    ///
+    /// Returns true on success, otherwise `data` is untouched.
+    pub fn read(&self, addr: u64, data: &mut [u8]) -> bool {
+        if let Some((offset, dev)) = self.get_device(addr) {
+            // OK to unwrap as lock() failing is a serious error condition and should panic.
+            dev.lock()
+                .expect("Failed to acquire device lock")
+                .read(offset, data);
+            true
+        } else {
+            false
+        }
+    }
+
+    /// Writes `data` to the device that owns the range containing `addr`.
+    ///
+    /// Returns true on success, otherwise `data` is untouched.
+    pub fn write(&self, addr: u64, data: &[u8]) -> bool {
+        if let Some((offset, dev)) = self.get_device(addr) {
+            // OK to unwrap as lock() failing is a serious error condition and should panic.
+            dev.lock()
+                .expect("Failed to acquire device lock")
+                .write(offset, data);
+            true
+        } else {
+            false
+        }
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    struct DummyDevice;
+    impl BusDevice for DummyDevice {}
+
+    struct ConstantDevice;
+    impl BusDevice for ConstantDevice {
+        fn read(&mut self, offset: u64, data: &mut [u8]) {
+            for (i, v) in data.iter_mut().enumerate() {
+                *v = (offset as u8) + (i as u8);
+            }
+        }
+
+        fn write(&mut self, offset: u64, data: &[u8]) {
+            for (i, v) in data.iter().enumerate() {
+                assert_eq!(*v, (offset as u8) + (i as u8))
+            }
+        }
+    }
+
+    #[test]
+    fn bus_insert() {
+        let mut bus = Bus::new();
+        let dummy = Arc::new(Mutex::new(DummyDevice));
+        assert!(bus.insert(dummy.clone(), 0x10, 0).is_err());
+        assert!(bus.insert(dummy.clone(), 0x10, 0x10).is_ok());
+
+        let result = bus.insert(dummy.clone(), 0x0f, 0x10);
+        assert!(result.is_err());
+        assert_eq!(format!("{:?}", result), "Err(Overlap)");
+
+        assert!(bus.insert(dummy.clone(), 0x10, 0x10).is_err());
+        assert!(bus.insert(dummy.clone(), 0x10, 0x15).is_err());
+        assert!(bus.insert(dummy.clone(), 0x12, 0x15).is_err());
+        assert!(bus.insert(dummy.clone(), 0x12, 0x01).is_err());
+        assert!(bus.insert(dummy.clone(), 0x0, 0x20).is_err());
+        assert!(bus.insert(dummy.clone(), 0x20, 0x05).is_ok());
+        assert!(bus.insert(dummy.clone(), 0x25, 0x05).is_ok());
+        assert!(bus.insert(dummy.clone(), 0x0, 0x10).is_ok());
+    }
+
+    #[test]
+    fn bus_read_write() {
+        let mut bus = Bus::new();
+        let dummy = Arc::new(Mutex::new(DummyDevice));
+        assert!(bus.insert(dummy.clone(), 0x10, 0x10).is_ok());
+        assert!(bus.read(0x10, &mut [0, 0, 0, 0]));
+        assert!(bus.write(0x10, &[0, 0, 0, 0]));
+        assert!(bus.read(0x11, &mut [0, 0, 0, 0]));
+        assert!(bus.write(0x11, &[0, 0, 0, 0]));
+        assert!(bus.read(0x16, &mut [0, 0, 0, 0]));
+        assert!(bus.write(0x16, &[0, 0, 0, 0]));
+        assert!(!bus.read(0x20, &mut [0, 0, 0, 0]));
+        assert!(!bus.write(0x20, &mut [0, 0, 0, 0]));
+        assert!(!bus.read(0x06, &mut [0, 0, 0, 0]));
+        assert!(!bus.write(0x06, &mut [0, 0, 0, 0]));
+    }
+
+    #[test]
+    fn bus_read_write_values() {
+        let mut bus = Bus::new();
+        let dummy = Arc::new(Mutex::new(ConstantDevice));
+        assert!(bus.insert(dummy.clone(), 0x10, 0x10).is_ok());
+
+        let mut values = [0, 1, 2, 3];
+        assert!(bus.read(0x10, &mut values));
+        assert_eq!(values, [0, 1, 2, 3]);
+        assert!(bus.write(0x10, &values));
+        assert!(bus.read(0x15, &mut values));
+        assert_eq!(values, [5, 6, 7, 8]);
+        assert!(bus.write(0x15, &values));
+    }
+
+    #[test]
+    fn busrange_cmp_and_clone() {
+        assert_eq!(BusRange(0x10, 2), BusRange(0x10, 3));
+        assert_eq!(BusRange(0x10, 2), BusRange(0x10, 2));
+
+        assert!(BusRange(0x10, 2) < BusRange(0x12, 1));
+        assert!(BusRange(0x10, 2) < BusRange(0x12, 3));
+
+        let bus_range = BusRange(0x10, 2);
+        assert_eq!(bus_range, bus_range.clone());
+
+        let mut bus = Bus::new();
+        let mut data = [1, 2, 3, 4];
+        assert!(bus
+            .insert(Arc::new(Mutex::new(DummyDevice)), 0x10, 0x10)
+            .is_ok());
+        assert!(bus.write(0x10, &mut data));
+        let bus_clone = bus.clone();
+        assert!(bus.read(0x10, &mut data));
+        assert_eq!(data, [1, 2, 3, 4]);
+        assert!(bus_clone.read(0x10, &mut data));
+        assert_eq!(data, [1, 2, 3, 4]);
+    }
+}
--- a/devices/src/legacy/mod.rs
+++ b/devices/src/legacy/mod.rs
@ -0,0 +1,10 @@
+// Copyright 2018 Amazon.com, Inc. or its affiliates. All Rights Reserved.
+// SPDX-License-Identifier: Apache-2.0
+//
+// Portions 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 THIRD-PARTY file.
+
+mod serial;
+
+pub use self::serial::Serial;
--- a/devices/src/legacy/serial.rs
+++ b/devices/src/legacy/serial.rs
@ -0,0 +1,384 @@
+// Copyright 2018 Amazon.com, Inc. or its affiliates. All Rights Reserved.
+// SPDX-License-Identifier: Apache-2.0
+//
+// Portions 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 THIRD-PARTY file.
+
+use std::collections::VecDeque;
+use std::{io, result};
+
+use vmm_sys_util::{EventFd, Result};
+
+use BusDevice;
+
+const LOOP_SIZE: usize = 0x40;
+
+const DATA: u8 = 0;
+const IER: u8 = 1;
+const IIR: u8 = 2;
+const LCR: u8 = 3;
+const MCR: u8 = 4;
+const LSR: u8 = 5;
+const MSR: u8 = 6;
+const SCR: u8 = 7;
+
+const DLAB_LOW: u8 = 0;
+const DLAB_HIGH: u8 = 1;
+
+const IER_RECV_BIT: u8 = 0x1;
+const IER_THR_BIT: u8 = 0x2;
+const IER_FIFO_BITS: u8 = 0x0f;
+
+const IIR_FIFO_BITS: u8 = 0xc0;
+const IIR_NONE_BIT: u8 = 0x1;
+const IIR_THR_BIT: u8 = 0x2;
+const IIR_RECV_BIT: u8 = 0x4;
+
+const LCR_DLAB_BIT: u8 = 0x80;
+
+const LSR_DATA_BIT: u8 = 0x1;
+const LSR_EMPTY_BIT: u8 = 0x20;
+const LSR_IDLE_BIT: u8 = 0x40;
+
+const MCR_LOOP_BIT: u8 = 0x10;
+
+const DEFAULT_INTERRUPT_IDENTIFICATION: u8 = IIR_NONE_BIT; // no pending interrupt
+const DEFAULT_LINE_STATUS: u8 = LSR_EMPTY_BIT | LSR_IDLE_BIT; // THR empty and line is idle
+const DEFAULT_LINE_CONTROL: u8 = 0x3; // 8-bits per character
+const DEFAULT_MODEM_CONTROL: u8 = 0x8; // Auxiliary output 2
+const DEFAULT_MODEM_STATUS: u8 = 0x20 | 0x10 | 0x80; // data ready, clear to send, carrier detect
+const DEFAULT_BAUD_DIVISOR: u16 = 12; // 9600 bps
+
+/// Emulates serial COM ports commonly seen on x86 I/O ports 0x3f8/0x2f8/0x3e8/0x2e8.
+///
+/// This can optionally write the guest's output to a Write trait object. To send input to the
+/// guest, use `queue_input_bytes`.
+pub struct Serial {
+    interrupt_enable: u8,
+    interrupt_identification: u8,
+    interrupt_evt: EventFd,
+    line_control: u8,
+    line_status: u8,
+    modem_control: u8,
+    modem_status: u8,
+    scratch: u8,
+    baud_divisor: u16,
+    in_buffer: VecDeque<u8>,
+    out: Option<Box<io::Write + Send>>,
+}
+
+impl Serial {
+    fn new(interrupt_evt: EventFd, out: Option<Box<io::Write + Send>>) -> Serial {
+        Serial {
+            interrupt_enable: 0,
+            interrupt_identification: DEFAULT_INTERRUPT_IDENTIFICATION,
+            interrupt_evt,
+            line_control: DEFAULT_LINE_CONTROL,
+            line_status: DEFAULT_LINE_STATUS,
+            modem_control: DEFAULT_MODEM_CONTROL,
+            modem_status: DEFAULT_MODEM_STATUS,
+            scratch: 0,
+            baud_divisor: DEFAULT_BAUD_DIVISOR,
+            in_buffer: VecDeque::new(),
+            out,
+        }
+    }
+
+    /// Constructs a Serial port ready for output.
+    pub fn new_out(interrupt_evt: EventFd, out: Box<io::Write + Send>) -> Serial {
+        Self::new(interrupt_evt, Some(out))
+    }
+
+    /// Constructs a Serial port with no connected output.
+    pub fn new_sink(interrupt_evt: EventFd) -> Serial {
+        Self::new(interrupt_evt, None)
+    }
+
+    /// Queues raw bytes for the guest to read and signals the interrupt if the line status would
+    /// change.
+    pub fn queue_input_bytes(&mut self, c: &[u8]) -> Result<()> {
+        if !self.is_loop() {
+            self.in_buffer.extend(c);
+            self.recv_data()?;
+        }
+        Ok(())
+    }
+
+    fn is_dlab_set(&self) -> bool {
+        (self.line_control & LCR_DLAB_BIT) != 0
+    }
+
+    fn is_recv_intr_enabled(&self) -> bool {
+        (self.interrupt_enable & IER_RECV_BIT) != 0
+    }
+
+    fn is_thr_intr_enabled(&self) -> bool {
+        (self.interrupt_enable & IER_THR_BIT) != 0
+    }
+
+    fn is_loop(&self) -> bool {
+        (self.modem_control & MCR_LOOP_BIT) != 0
+    }
+
+    fn add_intr_bit(&mut self, bit: u8) {
+        self.interrupt_identification &= !IIR_NONE_BIT;
+        self.interrupt_identification |= bit;
+    }
+
+    fn del_intr_bit(&mut self, bit: u8) {
+        self.interrupt_identification &= !bit;
+        if self.interrupt_identification == 0x0 {
+            self.interrupt_identification = IIR_NONE_BIT;
+        }
+    }
+
+    fn thr_empty(&mut self) -> Result<()> {
+        if self.is_thr_intr_enabled() {
+            self.add_intr_bit(IIR_THR_BIT);
+            self.trigger_interrupt()?
+        }
+        Ok(())
+    }
+
+    fn recv_data(&mut self) -> Result<()> {
+        if self.is_recv_intr_enabled() {
+            self.add_intr_bit(IIR_RECV_BIT);
+            self.trigger_interrupt()?
+        }
+        self.line_status |= LSR_DATA_BIT;
+        Ok(())
+    }
+
+    fn trigger_interrupt(&mut self) -> result::Result<(), io::Error> {
+        self.interrupt_evt.write(1)
+    }
+
+    fn iir_reset(&mut self) {
+        self.interrupt_identification = DEFAULT_INTERRUPT_IDENTIFICATION;
+    }
+
+    fn handle_write(&mut self, offset: u8, v: u8) -> Result<()> {
+        match offset as u8 {
+            DLAB_LOW if self.is_dlab_set() => {
+                self.baud_divisor = (self.baud_divisor & 0xff00) | u16::from(v)
+            }
+            DLAB_HIGH if self.is_dlab_set() => {
+                self.baud_divisor = (self.baud_divisor & 0x00ff) | ((u16::from(v)) << 8)
+            }
+            DATA => {
+                if self.is_loop() {
+                    if self.in_buffer.len() < LOOP_SIZE {
+                        self.in_buffer.push_back(v);
+                        self.recv_data()?;
+                    }
+                } else {
+                    if let Some(out) = self.out.as_mut() {
+                        out.write_all(&[v])?;
+                        out.flush()?;
+                    }
+                    self.thr_empty()?;
+                }
+            }
+            IER => self.interrupt_enable = v & IER_FIFO_BITS,
+            LCR => self.line_control = v,
+            MCR => self.modem_control = v,
+            SCR => self.scratch = v,
+            _ => {}
+        }
+        Ok(())
+    }
+}
+
+impl BusDevice for Serial {
+    fn read(&mut self, offset: u64, data: &mut [u8]) {
+        if data.len() != 1 {
+            return;
+        }
+
+        data[0] = match offset as u8 {
+            DLAB_LOW if self.is_dlab_set() => self.baud_divisor as u8,
+            DLAB_HIGH if self.is_dlab_set() => (self.baud_divisor >> 8) as u8,
+            DATA => {
+                self.del_intr_bit(IIR_RECV_BIT);
+                if self.in_buffer.len() <= 1 {
+                    self.line_status &= !LSR_DATA_BIT;
+                }
+                self.in_buffer.pop_front().unwrap_or_default()
+            }
+            IER => self.interrupt_enable,
+            IIR => {
+                let v = self.interrupt_identification | IIR_FIFO_BITS;
+                self.iir_reset();
+                v
+            }
+            LCR => self.line_control,
+            MCR => self.modem_control,
+            LSR => self.line_status,
+            MSR => self.modem_status,
+            SCR => self.scratch,
+            _ => 0,
+        };
+    }
+
+    fn write(&mut self, offset: u64, data: &[u8]) {
+        if data.len() != 1 {
+            return;
+        }
+
+        if let Err(_e) = self.handle_write(offset as u8, data[0]) {}
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use std::io;
+    use std::sync::{Arc, Mutex};
+
+    #[derive(Clone)]
+    struct SharedBuffer {
+        buf: Arc<Mutex<Vec<u8>>>,
+    }
+
+    impl SharedBuffer {
+        fn new() -> SharedBuffer {
+            SharedBuffer {
+                buf: Arc::new(Mutex::new(Vec::new())),
+            }
+        }
+    }
+
+    impl io::Write for SharedBuffer {
+        fn write(&mut self, buf: &[u8]) -> io::Result<usize> {
+            self.buf.lock().unwrap().write(buf)
+        }
+        fn flush(&mut self) -> io::Result<()> {
+            self.buf.lock().unwrap().flush()
+        }
+    }
+
+    #[test]
+    fn serial_output() {
+        let intr_evt = EventFd::new().unwrap();
+        let serial_out = SharedBuffer::new();
+
+        let mut serial = Serial::new_out(intr_evt, Box::new(serial_out.clone()));
+
+        serial.write(DATA as u64, &['x' as u8, 'y' as u8]);
+        serial.write(DATA as u64, &['a' as u8]);
+        serial.write(DATA as u64, &['b' as u8]);
+        serial.write(DATA as u64, &['c' as u8]);
+        assert_eq!(
+            serial_out.buf.lock().unwrap().as_slice(),
+            &['a' as u8, 'b' as u8, 'c' as u8]
+        );
+    }
+
+    #[test]
+    fn serial_input() {
+        let intr_evt = EventFd::new().unwrap();
+        let serial_out = SharedBuffer::new();
+
+        let mut serial =
+            Serial::new_out(intr_evt.try_clone().unwrap(), Box::new(serial_out.clone()));
+
+        // write 1 to the interrupt event fd, so that read doesn't block in case the event fd
+        // counter doesn't change (for 0 it blocks)
+        assert!(intr_evt.write(1).is_ok());
+        serial.write(IER as u64, &[IER_RECV_BIT]);
+        serial
+            .queue_input_bytes(&['a' as u8, 'b' as u8, 'c' as u8])
+            .unwrap();
+
+        assert_eq!(intr_evt.read().unwrap(), 2);
+
+        // check if reading in a 2-length array doesn't have side effects
+        let mut data = [0u8, 0u8];
+        serial.read(DATA as u64, &mut data[..]);
+        assert_eq!(data, [0u8, 0u8]);
+
+        let mut data = [0u8];
+        serial.read(LSR as u64, &mut data[..]);
+        assert_ne!(data[0] & LSR_DATA_BIT, 0);
+        serial.read(DATA as u64, &mut data[..]);
+        assert_eq!(data[0], 'a' as u8);
+        serial.read(DATA as u64, &mut data[..]);
+        assert_eq!(data[0], 'b' as u8);
+        serial.read(DATA as u64, &mut data[..]);
+        assert_eq!(data[0], 'c' as u8);
+
+        // check if reading from the largest u8 offset returns 0
+        serial.read(0xff, &mut data[..]);
+        assert_eq!(data[0], 0);
+    }
+
+    #[test]
+    fn serial_thr() {
+        let intr_evt = EventFd::new().unwrap();
+        let mut serial = Serial::new_sink(intr_evt.try_clone().unwrap());
+
+        // write 1 to the interrupt event fd, so that read doesn't block in case the event fd
+        // counter doesn't change (for 0 it blocks)
+        assert!(intr_evt.write(1).is_ok());
+        serial.write(IER as u64, &[IER_THR_BIT]);
+        serial.write(DATA as u64, &['a' as u8]);
+
+        assert_eq!(intr_evt.read().unwrap(), 2);
+        let mut data = [0u8];
+        serial.read(IER as u64, &mut data[..]);
+        assert_eq!(data[0] & IER_FIFO_BITS, IER_THR_BIT);
+        serial.read(IIR as u64, &mut data[..]);
+        assert_ne!(data[0] & IIR_THR_BIT, 0);
+    }
+
+    #[test]
+    fn serial_dlab() {
+        let mut serial = Serial::new_sink(EventFd::new().unwrap());
+
+        serial.write(LCR as u64, &[LCR_DLAB_BIT as u8]);
+        serial.write(DLAB_LOW as u64, &[0x12 as u8]);
+        serial.write(DLAB_HIGH as u64, &[0x34 as u8]);
+
+        let mut data = [0u8];
+        serial.read(LCR as u64, &mut data[..]);
+        assert_eq!(data[0], LCR_DLAB_BIT as u8);
+        serial.read(DLAB_LOW as u64, &mut data[..]);
+        assert_eq!(data[0], 0x12);
+        serial.read(DLAB_HIGH as u64, &mut data[..]);
+        assert_eq!(data[0], 0x34);
+    }
+
+    #[test]
+    fn serial_modem() {
+        let mut serial = Serial::new_sink(EventFd::new().unwrap());
+
+        serial.write(MCR as u64, &[MCR_LOOP_BIT as u8]);
+        serial.write(DATA as u64, &['a' as u8]);
+        serial.write(DATA as u64, &['b' as u8]);
+        serial.write(DATA as u64, &['c' as u8]);
+
+        let mut data = [0u8];
+        serial.read(MSR as u64, &mut data[..]);
+        assert_eq!(data[0], DEFAULT_MODEM_STATUS as u8);
+        serial.read(MCR as u64, &mut data[..]);
+        assert_eq!(data[0], MCR_LOOP_BIT as u8);
+        serial.read(DATA as u64, &mut data[..]);
+        assert_eq!(data[0], 'a' as u8);
+        serial.read(DATA as u64, &mut data[..]);
+        assert_eq!(data[0], 'b' as u8);
+        serial.read(DATA as u64, &mut data[..]);
+        assert_eq!(data[0], 'c' as u8);
+    }
+
+    #[test]
+    fn serial_scratch() {
+        let mut serial = Serial::new_sink(EventFd::new().unwrap());
+
+        serial.write(SCR as u64, &[0x12 as u8]);
+
+        let mut data = [0u8];
+        serial.read(SCR as u64, &mut data[..]);
+        assert_eq!(data[0], 0x12 as u8);
+    }
+}
--- a/devices/src/lib.rs
+++ b/devices/src/lib.rs
@ -0,0 +1,60 @@
+// Copyright 2018 Amazon.com, Inc. or its affiliates. All Rights Reserved.
+// SPDX-License-Identifier: Apache-2.0
+//
+// Portions 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 THIRD-PARTY file.
+
+//! Emulates virtual and hardware devices.
+extern crate byteorder;
+extern crate epoll;
+extern crate libc;
+
+extern crate vm_memory;
+extern crate vmm_sys_util;
+
+use std::fs::File;
+use std::io;
+
+mod bus;
+pub mod legacy;
+
+pub use self::bus::{Bus, BusDevice, Error as BusError};
+
+pub type DeviceEventT = u16;
+
+/// The payload is used to handle events where the internal state of the VirtIO device
+/// needs to be changed.
+pub enum EpollHandlerPayload {
+    /// DrivePayload(disk_image)
+    DrivePayload(File),
+    /// Events that do not need a payload.
+    Empty,
+}
+
+type Result<T> = std::result::Result<T, Error>;
+
+pub trait EpollHandler: Send {
+    fn handle_event(
+        &mut self,
+        device_event: DeviceEventT,
+        event_flags: u32,
+        payload: EpollHandlerPayload,
+    ) -> Result<()>;
+}
+
+#[derive(Debug)]
+pub enum Error {
+    FailedReadingQueue {
+        event_type: &'static str,
+        underlying: io::Error,
+    },
+    FailedReadTap,
+    FailedSignalingUsedQueue(io::Error),
+    PayloadExpected,
+    UnknownEvent {
+        device: &'static str,
+        event: DeviceEventT,
+    },
+    IoError(io::Error),
+}
--- a/src/main.rs
+++ b/src/main.rs
@ -12,6 +12,8 @@ use clap::{App, Arg};

 use std::path::PathBuf;

+use vmm::vm::*;
+
 fn main() {
    let cmd_arguments = App::new("cloud-hypervisor")
        .version(crate_version!())
@ -25,12 +27,16 @@ fn main() {
        )
        .get_matches();

-    let kernel_path = cmd_arguments
+    let kernel_arg = cmd_arguments
        .value_of("kernel")
        .map(PathBuf::from)
        .expect("Missing argument: kernel");

-    println!("Booting {:?}...", kernel_path.as_path());
+    let kernel_path = kernel_arg.as_path();

-    vmm::boot_kernel(kernel_path.as_path()).unwrap();
+    println!("Booting {:?}...", kernel_path);
+
+    let vm_config = VmConfig::new(kernel_path).unwrap();
+
+    vmm::boot_kernel(vm_config).unwrap();
 }
--- a/vmm/Cargo.toml
+++ b/vmm/Cargo.toml
@ -6,6 +6,7 @@ edition = "2018"

 [dependencies]
 arch = { path = "../arch" }
+devices = { path = "../devices" }
 kvm-bindings = "0.1"
 kvm-ioctls = { git = "https://github.com/rust-vmm/kvm-ioctls" }
 libc = ">=0.2.39"
--- a/vmm/src/lib.rs
+++ b/vmm/src/lib.rs
@ -6,10 +6,10 @@
 extern crate kvm_ioctls;

 use kvm_ioctls::*;
-use std::path::Path;
+
 pub mod vm;

-use self::vm::{Result, Vm};
+use self::vm::{Result, Vm, VmConfig};

 struct Vmm {
    kvm: Kvm,
@ -22,9 +22,9 @@ impl Vmm {
    }
 }

-pub fn boot_kernel(kernel: &Path) -> Result<()> {
+pub fn boot_kernel(config: VmConfig) -> Result<()> {
    let vmm = Vmm::new()?;
-    let mut vm = Vm::new(&vmm.kvm, kernel)?;
+    let mut vm = Vm::new(&vmm.kvm, config)?;

    let entry = vm.load_kernel()?;
    vm.start(entry)?;
--- a/vmm/src/vm.rs
+++ b/vmm/src/vm.rs
@ -4,6 +4,7 @@
 //

 extern crate arch;
+extern crate devices;
 extern crate kvm_ioctls;
 extern crate libc;
 extern crate linux_loader;
@ -12,21 +13,24 @@ extern crate vmm_sys_util;

 use kvm_bindings::{kvm_pit_config, kvm_userspace_memory_region, KVM_PIT_SPEAKER_DUMMY};
 use kvm_ioctls::*;
-use libc::{c_void, siginfo_t};
+use libc::{c_void, siginfo_t, EFD_NONBLOCK};
 use linux_loader::cmdline;
 use linux_loader::loader::KernelLoader;
 use std::ffi::CString;
 use std::fs::File;
+use std::io::{self, stdout};
 use std::path::Path;
-use std::sync::{Arc, Barrier};
-use std::{io, result, str, thread};
+use std::sync::{Arc, Barrier, Mutex};
+use std::{result, str, thread};
 use vm_memory::{
    Address, Bytes, GuestAddress, GuestMemory, GuestMemoryMmap, GuestMemoryRegion, GuestUsize,
    MmapError,
 };
 use vmm_sys_util::signal::register_signal_handler;
+use vmm_sys_util::EventFd;

 const VCPU_RTSIG_OFFSET: i32 = 0;
+pub const DEFAULT_VCPUS: u8 = 1;
 const DEFAULT_CMDLINE: &str = "console=ttyS0 reboot=k panic=1 pci=off nomodules \
                               i8042.noaux i8042.nomux i8042.nopnp i8042.dumbkbd";
 const CMDLINE_OFFSET: GuestAddress = GuestAddress(0x20000);
@ -86,6 +90,15 @@ pub enum Error {

    /// The call to KVM_SET_CPUID2 failed.
    SetSupportedCpusFailed(io::Error),
+
+    /// Cannot create EventFd.
+    EventFd(io::Error),
+
+    /// Cannot create a device manager.
+    DeviceManager,
+
+    /// Cannot add legacy device to Bus.
+    BusError(devices::BusError),
 }
 pub type Result<T> = result::Result<T, Error>;

@ -145,7 +158,7 @@ impl Vcpu {
    }
 }

-struct VmConfig<'a> {
+pub struct VmConfig<'a> {
    kernel_path: &'a Path,
    cmdline: Option<cmdline::Cmdline>,
    cmdline_addr: GuestAddress,
@ -154,6 +167,15 @@ struct VmConfig<'a> {
    vcpu_count: u8,
 }

+impl<'a> VmConfig<'a> {
+    pub fn new(kernel_path: &'a Path) -> Result<Self> {
+        Ok(VmConfig {
+            kernel_path,
+            ..Default::default()
+        })
+    }
+}
+
 impl<'a> Default for VmConfig<'a> {
    fn default() -> Self {
        let line = String::from(DEFAULT_CMDLINE);
@ -170,27 +192,56 @@ impl<'a> Default for VmConfig<'a> {
    }
 }

+struct DeviceManager {
+    io_bus: devices::Bus,
+
+    // Serial port on 0x3f8
+    serial: Arc<Mutex<devices::legacy::Serial>>,
+    serial_evt: EventFd,
+}
+
+impl DeviceManager {
+    fn new() -> Result<Self> {
+        let io_bus = devices::Bus::new();
+        let serial_evt = EventFd::new(EFD_NONBLOCK).map_err(Error::EventFd)?;
+        let serial = Arc::new(Mutex::new(devices::legacy::Serial::new_out(
+            serial_evt.try_clone().map_err(Error::EventFd)?,
+            Box::new(stdout()),
+        )));
+
+        Ok(DeviceManager {
+            io_bus,
+            serial,
+            serial_evt,
+        })
+    }
+
+    /// Register legacy devices.
+    pub fn register_devices(&mut self) -> Result<()> {
+        self.io_bus
+            .insert(self.serial.clone(), 0x3f8, 0x8)
+            .map_err(Error::BusError)?;
+        Ok(())
+    }
+}
+
 pub struct Vm<'a> {
    fd: VmFd,
    kernel: File,
    memory: GuestMemoryMmap,
    vcpus: Option<Vec<thread::JoinHandle<()>>>,
+    devices: DeviceManager,
    cpuid: CpuId,
    config: VmConfig<'a>,
 }

 impl<'a> Vm<'a> {
-    pub fn new(kvm: &Kvm, kernel_path: &'a Path) -> Result<Self> {
-        let vm_config = VmConfig {
-            kernel_path,
-            ..Default::default()
-        };
-
-        let kernel = File::open(kernel_path).map_err(Error::KernelFile)?;
+    pub fn new(kvm: &Kvm, config: VmConfig<'a>) -> Result<Self> {
+        let kernel = File::open(&config.kernel_path).map_err(Error::KernelFile)?;
        let fd = kvm.create_vm().map_err(Error::VmCreate)?;

        // Init guest memory
-        let arch_mem_regions = arch::arch_memory_regions(vm_config.memory_size << 20);
+        let arch_mem_regions = arch::arch_memory_regions(config.memory_size << 20);
        let guest_memory = GuestMemoryMmap::new(&arch_mem_regions).map_err(Error::GuestMemory)?;

        guest_memory
@ -232,13 +283,16 @@ impl<'a> Vm<'a> {
            .get_supported_cpuid(MAX_KVM_CPUID_ENTRIES)
            .map_err(Error::VmSetup)?;

+        let device_manager = DeviceManager::new().map_err(|_| Error::DeviceManager)?;
+
        Ok(Vm {
            fd,
            kernel,
            memory: guest_memory,
            vcpus: None,
+            devices: device_manager,
            cpuid,
-            config: vm_config,
+            config,
        })
    }

@ -274,6 +328,8 @@ impl<'a> Vm<'a> {
    }

    pub fn start(&mut self, entry_addr: GuestAddress) -> Result<()> {
+        self.devices.register_devices()?;
+
        let vcpu_count = self.config.vcpu_count;

        let mut vcpus: Vec<thread::JoinHandle<()>> = Vec::with_capacity(vcpu_count as usize);
@ -281,6 +337,7 @@ impl<'a> Vm<'a> {

        for cpu_id in 0..vcpu_count {
            println!("Starting VCPU {:?}", cpu_id);
+            let io_bus = self.devices.io_bus.clone();
            let mut vcpu = Vcpu::new(cpu_id, &self)?;
            vcpu.configure(entry_addr, &self)?;

@ -309,11 +366,11 @@ impl<'a> Vm<'a> {
                        loop {
                            match vcpu.run() {
                                Ok(run) => match run {
-                                    VcpuExit::IoIn(_addr, _data) => {}
+                                    VcpuExit::IoIn(addr, data) => {
+                                        io_bus.read(u64::from(addr), data);
+                                    }
                                    VcpuExit::IoOut(addr, data) => {
-                                        if addr == 0x3f8 {
-                                            print!("{}", str::from_utf8(&data).unwrap());
-                                        }
+                                        io_bus.write(u64::from(addr), data);
                                    }
                                    VcpuExit::MmioRead(addr, _data) => {
                                        println!("MMIO R -- addr: {:#x}", addr);