libkrun: enable legacy UART

enable-legacy-uart.diff

diff --git a/src/vmm/src/builder.rs b/src/vmm/src/builder.rs
index e67af76..b56ed94 100644
--- a/src/vmm/src/builder.rs
+++ b/src/vmm/src/builder.rs
@@ -10,7 +10,7 @@ use std::fmt::{Display, Formatter};
 use std::fs::File;
 use std::io::{self, Read};
 #[cfg(target_os = "linux")]
-use std::os::fd::AsRawFd;
+use std::os::fd::{RawFd, AsRawFd};
 use std::path::PathBuf;
 use std::sync::{Arc, Mutex};

@@ -65,6 +65,7 @@ use linux_loader::loader::{self, KernelLoader};
 use nix::unistd::isatty;
 use polly::event_manager::{Error as EventManagerError, EventManager};
 use utils::eventfd::EventFd;
+use utils::terminal::Terminal;
 #[cfg(all(target_arch = "x86_64", not(feature = "efi"), not(feature = "tee")))]
 use vm_memory::mmap::MmapRegion;
 #[cfg(not(feature = "tee"))]
@@ -436,6 +437,36 @@ impl Display for StartMicrovmError {
     }
 }

+// Wrapper over io::Stdin that implements `Serial::ReadableFd` and `vmm::VmmEventsObserver`.
+pub struct SerialStdin(io::Stdin);
+impl SerialStdin {
+    /// Returns a `SerialStdin` wrapper over `io::stdin`.
+    pub fn get() -> Self {
+        let stdin = io::stdin();
+        stdin.lock().set_raw_mode().unwrap();
+        SerialStdin(stdin)
+    }
+
+    pub fn restore() {
+        let stdin = io::stdin();
+        stdin.lock().set_canon_mode().unwrap();
+    }
+}
+
+impl io::Read for SerialStdin {
+    fn read(&mut self, buf: &mut [u8]) -> io::Result<usize> {
+        self.0.read(buf)
+    }
+}
+
+impl AsRawFd for SerialStdin {
+    fn as_raw_fd(&self) -> RawFd {
+        self.0.as_raw_fd()
+    }
+}
+
+impl devices::legacy::ReadableFd for SerialStdin {}
+
 enum Payload {
     #[cfg(all(target_arch = "x86_64", not(feature = "tee")))]
     KernelMmap,
@@ -588,13 +619,13 @@ pub fn build_microvm(

     // On x86_64 always create a serial device,
     // while on aarch64 only create it if 'console=' is specified in the boot args.
-    let serial_device = if cfg!(feature = "efi") {
+    let serial_device = if !cfg!(feature = "efi") {
         Some(setup_serial_device(
             event_manager,
-            None,
-            None,
+            Some(Box::new(SerialStdin::get())),
+            //None,
             // Uncomment this to get EFI output when debugging EDK2.
-            //Some(Box::new(io::stdout())),
+            Some(Box::new(io::stdout())),
         )?)
     } else {
         None