crosvm: Add flag to use legacy console

Some downstreams currently still use the legacy console. Some e2e_tests
(snapshot/restore) also will require using the legacy console, as the
AsyncConsole does not currently have an implementation for these
functions.

BUG=N/A
TEST=presubmit
TEST=run VM with legacy console flag

Change-Id: I97f94d79c6b0c2c23115283e1539f7cda580f5b8
Reviewed-on: https://chromium-review.googlesource.com/c/crosvm/crosvm/+/4618965
Reviewed-by: Noah Gold <nkgold@google.com>
Reviewed-by: Frederick Mayle <fmayle@google.com>
Commit-Queue: Elie Kheirallah <khei@google.com>

arch/src/serial.rs

@@ -187,7 +187,8 @@ pub fn get_serial_cmdline(
                 .insert("console", &format!("ttyS{}", num - 1))
                 .map_err(GetSerialCmdlineError::KernelCmdline)?;
         }
-        Some((SerialHardware::VirtioConsole, num)) => {
+        Some((SerialHardware::VirtioConsole, num))
+        | Some((SerialHardware::LegacyVirtioConsole, num)) => {
             cmdline
                 .insert("console", &format!("hvc{}", num - 1))
                 .map_err(GetSerialCmdlineError::KernelCmdline)?;

devices/src/serial_device.rs

@@ -103,9 +103,10 @@ impl Display for SerialType {
 #[derive(Copy, Clone, Debug, PartialEq, Eq, PartialOrd, Ord, Serialize, Deserialize)]
 #[serde(rename_all = "kebab-case")]
 pub enum SerialHardware {
-    Serial,        // Standard PC-style (8250/16550 compatible) UART
-    VirtioConsole, // virtio-console device
-    Debugcon,      // Bochs style debug port
+    Serial,              // Standard PC-style (8250/16550 compatible) UART
+    VirtioConsole,       // virtio-console device (AsyncConsole)
+    Debugcon,            // Bochs style debug port
+    LegacyVirtioConsole, // legacy virtio-console device (Console)
 }
 
 impl Default for SerialHardware {
@@ -120,6 +121,7 @@ impl Display for SerialHardware {
             SerialHardware::Serial => "serial".to_string(),
             SerialHardware::VirtioConsole => "virtio-console".to_string(),
             SerialHardware::Debugcon => "debugcon".to_string(),
+            SerialHardware::LegacyVirtioConsole => "legacy-virtio-console".to_string(),
         };
 
         write!(f, "{}", s)

src/crosvm/cmdline.rs

@@ -1864,7 +1864,7 @@ pub struct RunCommand {
     /// Possible key values:
     ///     type=(stdout,syslog,sink,file) - Where to route the
     ///        serial device
-    ///     hardware=(serial,virtio-console,debugcon) - Which type
+    ///     hardware=(serial,virtio-console,debugcon,legacy-virtio-console) - Which type
     ///        of serial hardware to emulate. Defaults to 8250 UART
     ///        (serial).
     ///     num=(1,2,3,4) - Serial Device Number. If not provided,

src/crosvm/sys/unix.rs

@@ -352,11 +352,10 @@ fn create_virtio_devices(
         }
     }
 
-    for (_, param) in cfg
-        .serial_parameters
-        .iter()
-        .filter(|(_k, v)| v.hardware == SerialHardware::VirtioConsole)
-    {
+    for (_, param) in cfg.serial_parameters.iter().filter(|(_k, v)| {
+        v.hardware == SerialHardware::VirtioConsole
+            || v.hardware == SerialHardware::LegacyVirtioConsole
+    }) {
         let dev = param.create_virtio_device_and_jail(cfg.protection_type, &cfg.jail_config)?;
         devs.push(dev);
     }

src/crosvm/sys/unix/device_helpers.rs

@@ -20,6 +20,7 @@ use anyhow::Result;
 use arch::VirtioDeviceStub;
 use base::ReadNotifier;
 use base::*;
+use devices::serial_device::SerialHardware;
 use devices::serial_device::SerialParameters;
 use devices::serial_device::SerialType;
 use devices::vfio::VfioCommonSetup;
@@ -45,6 +46,7 @@ use devices::virtio::vhost::user::VhostUserVsockDevice;
 use devices::virtio::vsock::VsockConfig;
 #[cfg(feature = "balloon")]
 use devices::virtio::BalloonMode;
+use devices::virtio::Console;
 use devices::virtio::NetError;
 use devices::virtio::NetParameters;
 use devices::virtio::NetParametersMode;
@@ -1346,10 +1348,17 @@ impl VirtioDeviceBuilder for &SerialParameters {
         let mut keep_rds = Vec::new();
         let evt = Event::new().context("failed to create event")?;
 
-        Ok(Box::new(
-            self.create_serial_device::<AsyncConsole>(protection_type, &evt, &mut keep_rds)
-                .context("failed to create console device")?,
-        ))
+        if self.hardware == SerialHardware::LegacyVirtioConsole {
+            Ok(Box::new(
+                self.create_serial_device::<Console>(protection_type, &evt, &mut keep_rds)
+                    .context("failed to create console device")?,
+            ))
+        } else {
+            Ok(Box::new(
+                self.create_serial_device::<AsyncConsole>(protection_type, &evt, &mut keep_rds)
+                    .context("failed to create console device")?,
+            ))
+        }
     }
 
     fn create_vhost_user_device(