Support graceful termination via SIGINT (#23)

* Support graceful termination via SIGINT

* $ cargo fmt

* Explain why we need to ignore the SIGINT

Cargo.toml

@@ -14,7 +14,7 @@ debug = true
 [dependencies]
 smoltcp = "0.8.1"
 libc = "0.2.126"
-polling = "2.2.0"
+polling = { git = "https://github.com/smol-rs/polling.git" }
 dhcproto = "0.7.0"
 vmnet = "0.1.1"
 clap = { version = "3.1.18", features = ["derive"] }
@@ -27,3 +27,4 @@ system-configuration = "0.5.0"
 num_enum = "0.5.7"
 sentry = { version = "0.29.1", features = ["debug-images"] }
 sentry-anyhow = { version = "0.29.1", features = ["backtrace"] }
+nix = "0.26.2"

lib/poller.rs

@@ -1,5 +1,7 @@
 use anyhow::Result;
 use num_enum::IntoPrimitive;
+use polling::os::kqueue::PollerKqueueExt;
+use polling::PollMode;
 use std::os::unix::io::RawFd;
 use std::time::Duration;
 
@@ -15,6 +17,7 @@ pub struct Poller {
 enum EventKey {
     VM,
     Host,
+    Interrupt,
 }
 
 impl Poller {
@@ -34,6 +37,15 @@ impl Poller {
         self.poller
             .add(self.host_fd as RawFd, self.host_interest())?;
 
+        let interrupt_signal = polling::os::kqueue::Signal(libc::SIGINT);
+        self.poller
+            .add_filter(
+                interrupt_signal,
+                EventKey::Interrupt.into(),
+                PollMode::Oneshot,
+            )
+            .unwrap();
+
         Ok(())
     }
 
@@ -45,10 +57,17 @@ impl Poller {
         self.poller
             .modify(self.host_fd as RawFd, self.host_interest())?;
 
+        let interrupt_signal = polling::os::kqueue::Signal(libc::SIGINT);
+        self.poller.modify_filter(
+            interrupt_signal,
+            EventKey::Interrupt.into(),
+            PollMode::Oneshot,
+        )?;
+
         Ok(())
     }
 
-    pub fn wait(&mut self) -> Result<(bool, bool)> {
+    pub fn wait(&mut self) -> Result<(bool, bool, bool)> {
         self.poller
             .wait(&mut self.events, Some(Duration::from_millis(100)))?;
 
@@ -60,8 +79,12 @@ impl Poller {
             .events
             .iter()
             .any(|ev| ev.key == Into::<usize>::into(EventKey::Host));
+        let interrupt = self
+            .events
+            .iter()
+            .any(|ev| ev.key == Into::<usize>::into(EventKey::Interrupt));
 
-        Ok((vm_readable, host_readable))
+        Ok((vm_readable, host_readable, interrupt))
     }
 
     fn vm_interest(&self) -> polling::Event {

lib/proxy/mod.rs

@@ -43,7 +43,7 @@ impl Proxy {
         self.poller.arm()?;
 
         loop {
-            let (vm_readable, host_readable) = self.poller.wait()?;
+            let (vm_readable, host_readable, interrupt) = self.poller.wait()?;
 
             if vm_readable {
                 self.read_from_vm(buf.as_mut_slice())?;
@@ -53,6 +53,11 @@ impl Proxy {
                 self.read_from_host(buf.as_mut_slice())?;
             }
 
+            // Graceful termination
+            if interrupt {
+                return Ok(());
+            }
+
             self.poller.rearm()?;
         }
     }

src/main.rs

@@ -1,5 +1,6 @@
 use anyhow::{anyhow, Context};
 use clap::Parser;
+use nix::sys::signal::{signal, SigHandler, Signal};
 use privdrop::PrivDrop;
 use softnet::proxy::Proxy;
 use std::borrow::Cow;
@@ -55,7 +56,7 @@ fn main() -> ExitCode {
 
     // Initialize Sentry
     let _sentry = sentry::init(sentry::ClientOptions {
-        release: option_env!("CIRRUS_TAG").map(|tag| { Cow::from(format!("softnet@{tag}")) }),
+        release: option_env!("CIRRUS_TAG").map(|tag| Cow::from(format!("softnet@{tag}"))),
         ..Default::default()
     });
 
@@ -84,6 +85,14 @@ fn main() -> ExitCode {
 }
 
 fn try_main() -> anyhow::Result<()> {
+    // The default signal(3)[1] action for SIGINT is to interrupt program,
+    // but we want to handle SIGINT ourselves, so we ignore it. The kqueue(2)'s[2]
+    // EVFILT_SIGNAL will receive it anyways, because it has lower precedence.
+    //
+    // [1]: https://developer.apple.com/library/archive/documentation/System/Conceptual/ManPages_iPhoneOS/man3/signal.3.html
+    // [2]: https://developer.apple.com/library/archive/documentation/System/Conceptual/ManPages_iPhoneOS/man2/kqueue.2.html
+    unsafe { signal(Signal::SIGINT, SigHandler::SigIgn) }?;
+
     let args: Args = Args::parse();
 
     // No need to run anything, just return