Allow overriding external binary paths via compile-time env vars

This is particularly useful for Nix, to avoid patching code when building.

Signed-off-by: Val Packett <[email protected]>

Author: valpackett

crates/muvm/src/guest/bin/muvm-guest.rs

@@ -77,7 +77,9 @@ fn main() -> Result<ExitCode> {
     rustix::stdio::dup2_stdout(console.as_fd())?;
     rustix::stdio::dup2_stderr(console.as_fd())?;
 
-    Command::new("/usr/lib/systemd/systemd-udevd").spawn()?;
+    Command::new(std::option_env!("MUVM_UDEVD_PATH").unwrap_or("/usr/lib/systemd/systemd-udevd"))
+        .spawn()
+        .context("Running systemd-udevd")?;
 
     if let Some(emulator) = options.emulator {
         match emulator {

crates/muvm/src/monitor.rs

@@ -49,7 +49,7 @@ fn set_guest_pressure(pressure: GuestPressure) -> Result<()> {
     let wsf: u32 = pressure.into();
     debug!("setting watermark_scale_factor to {wsf}");
 
-    let command = PathBuf::from("/sbin/sysctl");
+    let command = PathBuf::from(std::option_env!("MUVM_SYSCTL_PATH").unwrap_or("/sbin/sysctl"));
     let command_args = vec![format!("vm.watermark_scale_factor={}", wsf)];
     let env = HashMap::new();
     request_launch(command, command_args, env, 0, false, true)