auto-create inittab entries for serial consoles

src/cmd/init/bootstrap.rs

@@ -79,7 +79,30 @@ pub async fn bootstrap(cfg: Config) {
     })
     .await;
 
-    exec("chroot", &["/system", "update-ca-certificates"]).await
+    exec("chroot", &["/system", "update-ca-certificates"]).await;
+
+    // activate ttyS* consoles as needed
+    retry_or_ignore(async || {
+        const PATH: &str = "/system/etc/inittab";
+        let mut inittab = fs::read_to_string(PATH).await?;
+        let mut changed = false;
+        for opt in utils::cmdline().filter_map(|s| s.strip_prefix("console=ttyS")) {
+            info!("inittab: adding entry for ttyS{opt}");
+            changed = true;
+
+            let mut params = opt.split(',');
+            let num = params.next().unwrap();
+            let speed = params.next().unwrap_or("115200");
+            inittab.push_str(&format!(
+                "S{num}:12345:respawn:/sbin/agetty --noclear {speed} ttyS{num} linux\n"
+            ));
+        }
+        if changed {
+            fs::write(PATH, inittab.as_bytes()).await?;
+        }
+        Ok(())
+    })
+    .await;
 }
 
 struct Verifier {