From a81e6996193e0e0afa537736bdfc3d4e912f865d Mon Sep 17 00:00:00 2001
From: Valentin Haudiquet <valentin.haudiquet@canonical.com>
Date: Tue, 16 Jun 2026 23:38:09 +0200
Subject: [PATCH] fix: enable job control for shell with --kernel

---
 SPEC.md        |  3 ++-
 src/qemu_vm.rs | 55 +++++++++++++++++++++++++++++++++++++++++---------
 2 files changed, 48 insertions(+), 10 deletions(-)

diff --git a/SPEC.md b/SPEC.md
index 4d9d067..5009c2c 100644
--- a/SPEC.md
+++ b/SPEC.md
@@ -205,7 +205,8 @@ ecr --kernel /boot/vmlinuz debian -- /bin/sh -c "echo hello"
 4. Launch QEMU with:
    - `-kernel <path>` - provided kernel
    - `-initrd initramfs.cpio.gz` - rootfs as initramfs
-   - `-append "console=ttyS0 quiet rdinit=/bin/sh"` - kernel command line
+   - `-append "console=ttyS0 quiet rdinit=/bin/sh -- -c \"setsid sh -c 'exec sh </dev/ttyS0 >/dev/ttyS0 2>&1'\""` - kernel command line
+7. Essential device nodes (/dev/ttyS0, /dev/null, /dev/tty) are added to initramfs for proper console support
    - `-m <memory>` - memory size (default 2G)
    - `-display none -serial mon:stdio` - console on stdio
    - `-netdev user,id=net0 -device virtio-net-pci,netdev=net0` - network
diff --git a/src/qemu_vm.rs b/src/qemu_vm.rs
index f384ee9..8c9ac7b 100644
--- a/src/qemu_vm.rs
+++ b/src/qemu_vm.rs
@@ -57,15 +57,17 @@ pub fn launch_qemu(config: QemuConfig) -> Result<()> {
     // For initramfs boot, use rdinit= instead of init=
     // No root= needed as initramfs becomes the rootfs
     // 'quiet' suppresses kernel log messages for a cleaner console
+    // Use setsid with redirected stdio to get proper job control
+    // /dev/ttyS0 is created in the initramfs for serial console
     let kernel_append = if let Some(ref cmd) = config.command {
         let cmd_str = cmd.join(" ");
         format!(
-            "console=ttyS0 quiet rdinit=/bin/sh -- -c \"{}\"",
+            "console=ttyS0 quiet rdinit=/bin/sh -- -c \"setsid sh -c 'exec sh </dev/ttyS0 >/dev/ttyS0 2>&1 -c {}'\"",
             cmd_str
         )
     } else {
-        // Default to interactive shell
-        "console=ttyS0 quiet rdinit=/bin/sh".to_string()
+        // Default to interactive shell with proper job control
+        "console=ttyS0 quiet rdinit=/bin/sh -- -c \"setsid sh -c 'exec sh </dev/ttyS0 >/dev/ttyS0 2>&1'\"".to_string()
     };
 
     veprintln!("Launching QEMU: {}", qemu_bin);
@@ -175,22 +177,25 @@ fn create_cpio_archive(rootfs: &Path) -> Result<Vec<u8>> {
     // Collect all entries with their data
     let entries = collect_entries(rootfs, rootfs)?;
     
+    // Collect entry names for checking existence later
+    let entry_names: Vec<&str> = entries.iter().map(|(n, _, _, _, _)| n.as_str()).collect();
+    
     // Write each entry using the cpio crate
-    for (name, mode, mtime, nlink, data) in entries {
+    for (name, mode, mtime, nlink, data) in &entries {
         let file_size = data.len() as u32;
         
-        let builder = NewcBuilder::new(&name)
-            .mode(mode)
+        let builder = NewcBuilder::new(name)
+            .mode(*mode)
             .uid(0)
             .gid(0)
-            .nlink(nlink)
-            .mtime(mtime);
+            .nlink(*nlink)
+            .mtime(*mtime);
         
         // Write header and get a writer
         let mut writer = builder.write(&mut archive, file_size);
         
         // Write the file content
-        writer.write_all(&data)
+        writer.write_all(data)
             .context("Failed to write file content to cpio archive")?;
         
         // Finish this entry (returns the underlying writer)
@@ -198,6 +203,38 @@ fn create_cpio_archive(rootfs: &Path) -> Result<Vec<u8>> {
             .context("Failed to finish cpio entry")?;
     }
     
+    // Add essential device nodes for serial console
+    // These are character devices (mode 0o020xxx)
+    let device_nodes = [
+        // /dev/ttyS0 - serial console (major 4, minor 64)
+        ("dev/ttyS0", 0o020644, 4, 64),
+        // /dev/null (major 1, minor 3)
+        ("dev/null", 0o020644, 1, 3),
+        // /dev/tty - controlling terminal (major 5, minor 0)
+        ("dev/tty", 0o020666, 5, 0),
+    ];
+    
+    for (name, mode, major, minor) in device_nodes {
+        // Check if this device node already exists in the archive
+        if entry_names.contains(&name) {
+            continue;
+        }
+        
+        let builder = NewcBuilder::new(name)
+            .mode(mode)
+            .uid(0)
+            .gid(0)
+            .nlink(1)
+            .mtime(0)
+            .rdev_major(major)
+            .rdev_minor(minor);
+        
+        // Device nodes have zero size
+        let writer = builder.write(&mut archive, 0);
+        writer.finish()
+            .context("Failed to finish device node entry")?;
+    }
+    
     // Write the trailer (takes ownership and returns the writer)
     archive = newc::trailer(archive)
         .context("Failed to write cpio trailer")?;