vmm: reset to the original termios

Previously, we used two different functions for configuring ttys.
vmm_sys_util::terminal::Terminal::set_raw_mode() was used to configure
stdio ttys, and cfmakeraw() was used to configure ptys created by
cloud-hypervisor.  When I centralized the stdio tty cleanup, I also
switched to using cfmakeraw() everywhere, to avoid duplication.

cfmakeraw sets the OPOST flag, but when we later reset the ttys, we
used vmm_sys_util::terminal::Terminal::set_canon_mode(), which does
not unset this flag.  This meant that the terminal was getting mostly,
but not fully, reset.

To fix this without depending on the implementation of cfmakeraw(),
let's just store the original termios for stdio terminals, and restore
them to exactly the state we found them in when cloud-hypervisor exits.

Fixes: b6feae0a ("vmm: only touch the tty flags if it's being used")
Signed-off-by: Alyssa Ross <hi@alyssa.is>

vmm/src/vm.rs

@@ -55,7 +55,7 @@ use gdbstub_arch::aarch64::reg::AArch64CoreRegs as CoreRegs;
 #[cfg(all(target_arch = "x86_64", feature = "guest_debug"))]
 use gdbstub_arch::x86::reg::X86_64CoreRegs as CoreRegs;
 use hypervisor::{HypervisorVmError, VmOps};
-use libc::SIGWINCH;
+use libc::{termios, SIGWINCH};
 use linux_loader::cmdline::Cmdline;
 #[cfg(all(target_arch = "x86_64", feature = "guest_debug"))]
 use linux_loader::elf;
@@ -79,7 +79,6 @@ use std::mem::size_of;
 use std::num::Wrapping;
 use std::ops::Deref;
 use std::os::unix::net::UnixStream;
-use std::sync::atomic::AtomicBool;
 use std::sync::{Arc, Mutex, RwLock};
 use std::time::Instant;
 use std::{result, str, thread};
@@ -464,7 +463,7 @@ impl Vm {
         serial_pty: Option<PtyPair>,
         console_pty: Option<PtyPair>,
         console_resize_pipe: Option<File>,
-        on_tty: Arc<AtomicBool>,
+        original_termios: Arc<Mutex<Option<termios>>>,
         snapshot: Option<Snapshot>,
     ) -> Result<Self> {
         trace_scoped!("Vm::new_from_memory_manager");
@@ -586,7 +585,12 @@ impl Vm {
         device_manager
             .lock()
             .unwrap()
-            .create_devices(serial_pty, console_pty, console_resize_pipe, on_tty)
+            .create_devices(
+                serial_pty,
+                console_pty,
+                console_resize_pipe,
+                original_termios,
+            )
             .map_err(Error::DeviceManager)?;
 
         #[cfg(feature = "tdx")]
@@ -736,7 +740,7 @@ impl Vm {
         serial_pty: Option<PtyPair>,
         console_pty: Option<PtyPair>,
         console_resize_pipe: Option<File>,
-        on_tty: Arc<AtomicBool>,
+        original_termios: Arc<Mutex<Option<termios>>>,
         snapshot: Option<Snapshot>,
         source_url: Option<&str>,
         prefault: Option<bool>,
@@ -806,7 +810,7 @@ impl Vm {
             serial_pty,
             console_pty,
             console_resize_pipe,
-            on_tty,
+            original_termios,
             snapshot,
         )
     }