vm-virtio: Add virtio-rng implementation

Most of the code is taken from crosvm(bbd24c5) but is modified to
be adapted to the current VirtioDevice definition and epoll
implementation.

A new command option '--rng' is provided and it gives one the option
to override the entropy source which is /dev/urandom by default.

Signed-off-by: Chao Peng <chao.p.peng@linux.intel.com>

src/main.rs

@@ -55,6 +55,12 @@ fn main() {
                 .help("Amount of RAM (in MB)")
                 .takes_value(true),
         )
+        .arg(
+            Arg::with_name("rng")
+                .long("rng")
+                .help("Path to entropy source")
+                .default_value("/dev/urandom"),
+        )
         .get_matches();
 
     let kernel_arg = cmd_arguments
@@ -79,6 +85,11 @@ fn main() {
         net_params = Some(net.to_string());
     }
 
+    let rng_path = match cmd_arguments.occurrences_of("rng") {
+        0 => None,
+        _ => Some(cmd_arguments.value_of("rng").unwrap().to_string()),
+    };
+
     let mut vcpus = DEFAULT_VCPUS;
     if let Some(cpus) = cmd_arguments.value_of("cpus") {
         vcpus = cpus.parse::<u8>().unwrap();
@@ -92,8 +103,16 @@ fn main() {
     println!("VM [{} vCPUS {} MB of memory]", vcpus, memory);
     println!("Booting {:?}...", kernel_path);
 
-    let vm_config =
-        VmConfig::new(kernel_path, disk_path, cmdline, net_params, vcpus, memory).unwrap();
+    let vm_config = VmConfig::new(
+        kernel_path,
+        disk_path,
+        rng_path,
+        cmdline,
+        net_params,
+        vcpus,
+        memory,
+    )
+    .unwrap();
 
     vmm::boot_kernel(vm_config).unwrap();
 }

vm-virtio/src/lib.rs

@@ -24,6 +24,7 @@ mod block;
 mod device;
 pub mod net;
 mod queue;
+mod rng;
 
 pub mod transport;
 
@@ -31,6 +32,7 @@ pub use self::block::*;
 pub use self::device::*;
 pub use self::net::*;
 pub use self::queue::*;
+pub use self::rng::*;
 
 const DEVICE_INIT: u32 = 0x00;
 const DEVICE_ACKNOWLEDGE: u32 = 0x01;

vm-virtio/src/rng.rs

@@ -0,0 +1,279 @@
+// 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 epoll;
+use libc::EFD_NONBLOCK;
+use std;
+use std::fs::File;
+use std::io;
+use std::os::unix::io::AsRawFd;
+use std::result;
+use std::sync::atomic::{AtomicUsize, Ordering};
+use std::sync::Arc;
+use std::thread;
+
+use super::Error as DeviceError;
+use super::{
+    ActivateError, ActivateResult, DeviceEventT, Queue, VirtioDevice, VirtioDeviceType,
+    INTERRUPT_STATUS_USED_RING, VIRTIO_F_VERSION_1,
+};
+
+use vm_memory::{Bytes, GuestMemoryMmap};
+use vmm_sys_util::EventFd;
+
+const QUEUE_SIZE: u16 = 256;
+const NUM_QUEUES: usize = 1;
+const QUEUE_SIZES: &[u16] = &[QUEUE_SIZE];
+
+// New descriptors are pending on the virtio queue.
+const QUEUE_AVAIL_EVENT: DeviceEventT = 0;
+// The device has been dropped.
+const KILL_EVENT: DeviceEventT = 1;
+
+struct RngEpollHandler {
+    queues: Vec<Queue>,
+    mem: GuestMemoryMmap,
+    random_file: File,
+    interrupt_status: Arc<AtomicUsize>,
+    interrupt_evt: EventFd,
+    queue_evt: EventFd,
+    kill_evt: EventFd,
+}
+
+impl RngEpollHandler {
+    fn process_queue(&mut self) -> bool {
+        let queue = &mut self.queues[0];
+
+        let mut used_desc_heads = [(0, 0); QUEUE_SIZE as usize];
+        let mut used_count = 0;
+        for avail_desc in queue.iter(&self.mem) {
+            let mut len = 0;
+
+            // Drivers can only read from the random device.
+            if avail_desc.is_write_only() {
+                // Fill the read with data from the random device on the host.
+                if self
+                    .mem
+                    .read_from(
+                        avail_desc.addr,
+                        &mut self.random_file,
+                        avail_desc.len as usize,
+                    )
+                    .is_ok()
+                {
+                    len = avail_desc.len;
+                }
+            }
+
+            used_desc_heads[used_count] = (avail_desc.index, len);
+            used_count += 1;
+        }
+
+        for &(desc_index, len) in &used_desc_heads[..used_count] {
+            queue.add_used(&self.mem, desc_index, len);
+        }
+        used_count > 0
+    }
+
+    fn signal_used_queue(&self) -> result::Result<(), DeviceError> {
+        self.interrupt_status
+            .fetch_or(INTERRUPT_STATUS_USED_RING as usize, Ordering::SeqCst);
+        self.interrupt_evt.write(1).map_err(|e| {
+            error!("Failed to signal used queue: {:?}", e);
+            DeviceError::FailedSignalingUsedQueue(e)
+        })
+    }
+
+    fn run(&mut self) -> result::Result<(), DeviceError> {
+        // Create the epoll file descriptor
+        let epoll_fd = epoll::create(true).map_err(DeviceError::EpollCreateFd)?;
+
+        // Add events
+        epoll::ctl(
+            epoll_fd,
+            epoll::ControlOptions::EPOLL_CTL_ADD,
+            self.queue_evt.as_raw_fd(),
+            epoll::Event::new(epoll::Events::EPOLLIN, u64::from(QUEUE_AVAIL_EVENT)),
+        )
+        .map_err(DeviceError::EpollCtl)?;
+        epoll::ctl(
+            epoll_fd,
+            epoll::ControlOptions::EPOLL_CTL_ADD,
+            self.kill_evt.as_raw_fd(),
+            epoll::Event::new(epoll::Events::EPOLLIN, u64::from(KILL_EVENT)),
+        )
+        .map_err(DeviceError::EpollCtl)?;
+
+        const EPOLL_EVENTS_LEN: usize = 100;
+        let mut events = vec![epoll::Event::new(epoll::Events::empty(), 0); EPOLL_EVENTS_LEN];
+
+        'epoll: loop {
+            let num_events =
+                epoll::wait(epoll_fd, -1, &mut events[..]).map_err(DeviceError::EpollWait)?;
+
+            for event in events.iter().take(num_events) {
+                let ev_type = event.data as u16;
+
+                match ev_type {
+                    QUEUE_AVAIL_EVENT => {
+                        if let Err(e) = self.queue_evt.read() {
+                            error!("Failed to get queue event: {:?}", e);
+                            break 'epoll;
+                        } else if self.process_queue() {
+                            if let Err(e) = self.signal_used_queue() {
+                                error!("Failed to signal used queue: {:?}", e);
+                                break 'epoll;
+                            }
+                        }
+                    }
+                    KILL_EVENT => {
+                        debug!("KILL_EVENT received, stopping epoll loop");
+                        break 'epoll;
+                    }
+                    _ => {
+                        error!("Unknown event for virtio-block");
+                    }
+                }
+            }
+        }
+
+        Ok(())
+    }
+}
+
+/// Virtio device for exposing entropy to the guest OS through virtio.
+pub struct Rng {
+    kill_evt: Option<EventFd>,
+    random_file: Option<File>,
+    avail_features: u64,
+    acked_features: u64,
+}
+
+impl Rng {
+    /// Create a new virtio rng device that gets random data from /dev/urandom.
+    pub fn new(path: &str) -> io::Result<Rng> {
+        let random_file = File::open(path)?;
+        let avail_features = 1u64 << VIRTIO_F_VERSION_1;
+
+        Ok(Rng {
+            kill_evt: None,
+            random_file: Some(random_file),
+            avail_features,
+            acked_features: 0u64,
+        })
+    }
+}
+
+impl Drop for Rng {
+    fn drop(&mut self) {
+        if let Some(kill_evt) = self.kill_evt.take() {
+            // Ignore the result because there is nothing we can do about it.
+            let _ = kill_evt.write(1);
+        }
+    }
+}
+
+impl VirtioDevice for Rng {
+    fn device_type(&self) -> u32 {
+        VirtioDeviceType::TYPE_RNG as u32
+    }
+
+    fn queue_max_sizes(&self) -> &[u16] {
+        QUEUE_SIZES
+    }
+
+    fn features(&self, page: u32) -> u32 {
+        match page {
+            // Get the lower 32-bits of the features bitfield.
+            0 => self.avail_features as u32,
+            // Get the upper 32-bits of the features bitfield.
+            1 => (self.avail_features >> 32) as u32,
+            _ => {
+                warn!("Received request for unknown features page.");
+                0u32
+            }
+        }
+    }
+
+    fn ack_features(&mut self, page: u32, value: u32) {
+        let mut v = match page {
+            0 => u64::from(value),
+            1 => u64::from(value) << 32,
+            _ => {
+                warn!("Cannot acknowledge unknown features page.");
+                0u64
+            }
+        };
+
+        // Check if the guest is ACK'ing a feature that we didn't claim to have.
+        let unrequested_features = v & !self.avail_features;
+        if unrequested_features != 0 {
+            warn!("Received acknowledge request for unknown feature.");
+
+            // Don't count these features as acked.
+            v &= !unrequested_features;
+        }
+        self.acked_features |= v;
+    }
+
+    fn read_config(&self, _offset: u64, _data: &mut [u8]) {
+        warn!("No currently device specific configration defined");
+    }
+
+    fn write_config(&mut self, _offset: u64, _data: &[u8]) {
+        warn!("No currently device specific configration defined");
+    }
+
+    fn activate(
+        &mut self,
+        mem: GuestMemoryMmap,
+        interrupt_evt: EventFd,
+        status: Arc<AtomicUsize>,
+        queues: Vec<Queue>,
+        mut queue_evts: Vec<EventFd>,
+    ) -> ActivateResult {
+        if queues.len() != NUM_QUEUES || queue_evts.len() != NUM_QUEUES {
+            error!(
+                "Cannot perform activate. Expected {} queue(s), got {}",
+                NUM_QUEUES,
+                queues.len()
+            );
+            return Err(ActivateError::BadActivate);
+        }
+
+        let (self_kill_evt, kill_evt) =
+            match EventFd::new(EFD_NONBLOCK).and_then(|e| Ok((e.try_clone()?, e))) {
+                Ok(v) => v,
+                Err(e) => {
+                    error!("failed creating kill EventFd pair: {}", e);
+                    return Err(ActivateError::BadActivate);
+                }
+            };
+        self.kill_evt = Some(self_kill_evt);
+
+        if let Some(random_file) = self.random_file.take() {
+            let mut handler = RngEpollHandler {
+                queues,
+                mem,
+                random_file,
+                interrupt_status: status,
+                interrupt_evt,
+                queue_evt: queue_evts.remove(0),
+                kill_evt,
+            };
+
+            let worker_result = thread::Builder::new()
+                .name("virtio_rng".to_string())
+                .spawn(move || handler.run());
+
+            if let Err(e) = worker_result {
+                error!("failed to spawn virtio_rng worker: {}", e);
+                return Err(ActivateError::BadActivate);;
+            }
+
+            return Ok(());
+        }
+        Err(ActivateError::BadActivate)
+    }
+}

vmm/src/vm.rs

@@ -158,6 +158,9 @@ pub enum Error {
     /// Cannot create virtio-net device
     CreateVirtioNet(vm_virtio::net::Error),
 
+    /// Cannot create virtio-rng device
+    CreateVirtioRng(io::Error),
+
     /// Cannot create the system allocator
     CreateSystemAllocator,
 
@@ -225,6 +228,7 @@ impl Vcpu {
 pub struct VmConfig<'a> {
     kernel_path: &'a Path,
     disk_path: &'a Path,
+    rng_path: Option<String>,
     cmdline: cmdline::Cmdline,
     cmdline_addr: GuestAddress,
     net_params: Option<String>,
@@ -236,6 +240,7 @@ impl<'a> VmConfig<'a> {
     pub fn new(
         kernel_path: &'a Path,
         disk_path: &'a Path,
+        rng_path: Option<String>,
         cmdline_str: String,
         net_params: Option<String>,
         vcpus: u8,
@@ -247,6 +252,7 @@ impl<'a> VmConfig<'a> {
         Ok(VmConfig {
             kernel_path,
             disk_path,
+            rng_path,
             cmdline,
             cmdline_addr: CMDLINE_OFFSET,
             net_params,
@@ -357,6 +363,21 @@ impl DeviceManager {
             }
         }
 
+        // Add virtio-rng if required
+        if let Some(rng_path) = &vm_cfg.rng_path {
+            let virtio_rng_device =
+                vm_virtio::Rng::new(rng_path).map_err(Error::CreateVirtioRng)?;
+
+            DeviceManager::add_virtio_pci_device(
+                Box::new(virtio_rng_device),
+                memory.clone(),
+                allocator,
+                vm_fd,
+                &mut pci_root,
+                &mut mmio_bus,
+            )?;
+        }
+
         let pci = Arc::new(Mutex::new(PciConfigIo::new(pci_root)));
 
         Ok(DeviceManager {