feat: use cpio crate for initramfs creation

Add the `cpio` crate as dependency, removing e2fsprogs external dependency.

Cargo.lock

@@ -243,6 +243,12 @@ version = "0.8.7"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "773648b94d0e5d620f64f280777445740e61fe701025087ec8b57f45c791888b"
 
+[[package]]
+name = "cpio"
+version = "0.4.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "938e716cb1ade5d6c8f959c13a7248b889c07491fc7e41167c3afe20f8f0de1e"
+
 [[package]]
 name = "crc32fast"
 version = "1.5.0"
@@ -296,6 +302,7 @@ version = "0.1.0"
 dependencies = [
  "anyhow",
  "clap",
+ "cpio",
  "dirs",
  "flate2",
  "futures-util",

Cargo.toml

@@ -36,6 +36,7 @@ anyhow = "1"
 # Utilities
 dirs = "6"
 which = "7"
+cpio = "0.4"
 tokio = { version = "1", features = ["rt-multi-thread", "macros", "io-util"] }
 futures-util = "0.3"
 indicatif = "0.18"

README.md

@@ -59,7 +59,7 @@ ecr --arch arm64 alpine -- uname -m
 # Always pull a fresh image
 ecr --no-cache fedora
 
-# Boot with QEMU system emulation (requires qemu-system-<arch> and e2fsprogs)
+# Boot with QEMU system emulation (requires qemu-system-<arch>)
 ecr --kernel /boot/vmlinuz ubuntu
 
 # Boot with custom memory
@@ -75,15 +75,14 @@ ecr --kernel /boot/vmlinuz alpine
 ```
 
 This mode:
-- Creates an ext4 disk image from the rootfs
+- Creates a gzipped CPIO initramfs from the rootfs
 - Boots QEMU with your kernel
 - Provides full VM isolation
 - Works for any architecture (no binfmt_misc needed)
 
 Requirements:
 - `qemu-system-<arch>` installed
-- `e2fsprogs` for disk image creation
+- Kernel with serial console support
-- Kernel with virtio support
 
 ## Supported distributions
 

SPEC.md

@@ -187,7 +187,7 @@ No action required. Modern qemu-user-static packages register binfmt_misc with t
 
 ## QEMU System Emulation Mode
 
-When `--kernel` is specified, ecr switches from namespace/chroot mode to QEMU system emulation. The extracted rootfs is converted to a disk image and booted with the provided kernel.
+When `--kernel` is specified, ecr switches from namespace/chroot mode to QEMU system emulation. The extracted rootfs is converted to a gzipped CPIO initramfs and booted with the provided kernel.
 
 ### Usage
 
@@ -201,24 +201,20 @@ ecr --kernel /boot/vmlinuz debian -- /bin/sh -c "echo hello"
 
 1. Download/cache rootfs tarball (same as namespace mode)
 2. Extract tarball to temporary directory
-3. Create ext4 disk image from rootfs using `mke2fs -d` (requires `e2fsprogs`)
+3. Create gzipped CPIO initramfs from rootfs
 4. Launch QEMU with:
    - `-kernel <path>` - provided kernel
-   - `-append "root=/dev/vda rw console=ttyS0"` - kernel command line
+   - `-initrd initramfs.cpio.gz` - rootfs as initramfs
+   - `-append "console=ttyS0 rdinit=/bin/sh"` - kernel command line
    - `-m <memory>` - memory size (default 2G)
-   - `-nographic` - console on stdio
+   - `-display none -serial mon:stdio` - console on stdio
-   - `-drive file=rootfs.img,format=raw,if=virtio` - rootfs disk
    - `-netdev user,id=net0 -device virtio-net-pci,netdev=net0` - network
 5. Wait for QEMU to exit
 6. Cleanup temporary files
 
-### Disk Image Creation
+### Initramfs Creation
 
-The rootfs directory is converted to an ext4 disk image using `mke2fs -t ext4 -d <rootfs>`. This requires the `e2fsprogs` package:
+The rootfs directory is converted to a gzipped CPIO archive (newc format) using  the `cpio` crate.
-
-- Ubuntu/Debian: `sudo apt install e2fsprogs`
-- Arch: `sudo pacman -S e2fsprogs`
-- Alpine: `sudo apk add e2fsprogs`
 
 ### Architecture Support
 
@@ -234,8 +230,7 @@ The rootfs directory is converted to an ext4 disk image using `mke2fs -t ext4 -d
 ### Requirements
 
 - QEMU system emulator installed (`qemu-system-<arch>`)
-- `e2fsprogs` for disk image creation
+- Kernel with required drivers (serial console, virtio-net for network)
-- Kernel with virtio support (for disk and network drivers)
 
 ### Differences from Namespace Mode
 

src/qemu_vm.rs

@@ -1,8 +1,10 @@
 use crate::veprintln;
 use anyhow::{anyhow, Context, Result};
+use cpio::{newc, NewcBuilder};
 use std::io::Write;
-use std::path::PathBuf;
+use std::os::unix::fs::MetadataExt;
-use std::process::{Command, Stdio};
+use std::path::{Path, PathBuf};
+use std::process::Command;
 
 /// QEMU system emulation configuration
 pub struct QemuConfig {
@@ -36,8 +38,8 @@ pub fn launch_qemu(config: QemuConfig) -> Result<()> {
         ));
     }
 
-    // Create a disk image from the rootfs
+    // Create a gzipped cpio initramfs from the rootfs
-    let disk_image = create_disk_image(&config.rootfs_path)?;
+    let initramfs = create_initramfs(&config.rootfs_path)?;
 
     // Get QEMU binary for architecture
     let qemu_bin = qemu_binary_for_arch(&config.arch);
@@ -52,22 +54,22 @@ pub fn launch_qemu(config: QemuConfig) -> Result<()> {
     ))?;
 
     // Build kernel command line
-    // Container rootfs images don't have /sbin/init - they expect a command as PID 1
+    // For initramfs boot, use rdinit= instead of init=
-    // We use init=/bin/sh as default, and if a command is specified, we pass it to sh
+    // No root= needed as initramfs becomes the rootfs
     let kernel_append = if let Some(ref cmd) = config.command {
         let cmd_str = cmd.join(" ");
         format!(
-            "root=/dev/vda rw console=ttyS0 init=/bin/sh -- -c \"{}\"",
+            "console=ttyS0 rdinit=/bin/sh -- -c \"{}\"",
             cmd_str
         )
     } else {
         // Default to interactive shell
-        "root=/dev/vda rw console=ttyS0 init=/bin/sh".to_string()
+        "console=ttyS0 rdinit=/bin/sh".to_string()
     };
 
     veprintln!("Launching QEMU: {}", qemu_bin);
     veprintln!("  Kernel: {}", config.kernel_path.display());
-    veprintln!("  Disk image: {}", disk_image.display());
+    veprintln!("  Initramfs: {}", initramfs.display());
     veprintln!("  Memory: {}", config.memory);
     veprintln!("  Kernel append: {}", kernel_append);
 
@@ -77,6 +79,8 @@ pub fn launch_qemu(config: QemuConfig) -> Result<()> {
     let args = vec![
         "-kernel".to_string(),
         config.kernel_path.to_string_lossy().to_string(),
+        "-initrd".to_string(),
+        initramfs.to_string_lossy().to_string(),
         "-append".to_string(),
         kernel_append,
         "-m".to_string(),
@@ -85,11 +89,6 @@ pub fn launch_qemu(config: QemuConfig) -> Result<()> {
         "none".to_string(),
         "-serial".to_string(),
         "mon:stdio".to_string(),
-        "-drive".to_string(),
-        format!(
-            "file={},format=raw,if=virtio",
-            disk_image.to_string_lossy()
-        ),
         "-netdev".to_string(),
         "user,id=net0".to_string(),
         "-device".to_string(),
@@ -102,9 +101,9 @@ pub fn launch_qemu(config: QemuConfig) -> Result<()> {
         .status()
         .context("Failed to execute QEMU")?;
 
-    // Cleanup disk image
+    // Cleanup initramfs
-    if let Err(e) = std::fs::remove_file(&disk_image) {
+    if let Err(e) = std::fs::remove_file(&initramfs) {
-        veprintln!("Warning: failed to cleanup disk image: {}", e);
+        veprintln!("Warning: failed to cleanup initramfs: {}", e);
     }
 
     if !status.success() {
@@ -143,203 +142,144 @@ fn get_arch_package_suffix(arch: &str) -> &str {
     }
 }
 
-/// Create a raw disk image from a directory
+/// Create a gzipped cpio initramfs from a directory
-fn create_disk_image(rootfs: &PathBuf) -> Result<PathBuf> {
+fn create_initramfs(rootfs: &PathBuf) -> Result<PathBuf> {
-    veprintln!("Creating disk image from rootfs...");
+    veprintln!("Creating initramfs from rootfs...");
 
-    // Create a temporary file for the disk image
+    // Create a temporary file for the initramfs
-    let disk_image = rootfs.parent().unwrap().join("rootfs.img");
+    let initramfs_path = rootfs.parent().unwrap().join("initramfs.cpio.gz");
 
-    // Use mke2fs to create an ext4 filesystem image
+    // Create the cpio archive
-    // First, calculate size needed (du -sb)
+    let cpio_data = create_cpio_archive(rootfs)?;
-    let du_output = Command::new("du")
-        .arg("-sb")
-        .arg(rootfs)
-        .output()
-        .context("Failed to calculate rootfs size")?;
 
-    let size_str = String::from_utf8_lossy(&du_output.stdout);
+    // Compress with gzip
-    let size: u64 = size_str
+    let mut output_file = std::fs::File::create(&initramfs_path)
-        .split_whitespace()
+        .context("Failed to create initramfs file")?;
-        .next()
-        .context("Failed to parse du output")?
-        .parse()
-        .context("Failed to parse size")?;
     
-    // Add 50% overhead for filesystem metadata, journal, and some free space
+    let mut encoder = flate2::write::GzEncoder::new(&mut output_file, flate2::Compression::default());
-    // ext4 with journal can have significant overhead
+    encoder.write_all(&cpio_data)
-    let image_size = size + (size / 2);
+        .context("Failed to write compressed initramfs")?;
-    // Minimum 64MB for small rootfs to ensure enough space for metadata
+    encoder.finish()
-    let image_size = image_size.max(64 * 1024 * 1024);
+        .context("Failed to finalize gzip compression")?;
 
-    veprintln!("Rootfs size: {} bytes, image size: {} bytes", size, image_size);
+    veprintln!("Initramfs created: {} bytes (uncompressed)", cpio_data.len());
 
-    // Create the image file
+    Ok(initramfs_path)
-    let image_file = std::fs::File::create(&disk_image)
-        .context("Failed to create disk image file")?;
-    
-    // Pre-allocate the file
-    image_file
-        .set_len(image_size)
-        .context("Failed to allocate disk image")?;
-    drop(image_file);
-
-    // Try to use mke2fs to create an ext4 image with the directory contents
-    // This is the most efficient way on Linux
-    veprintln!("Running: mke2fs -t ext4 -d {} {}", rootfs.display(), disk_image.display());
-    let mke2fs_result = Command::new("mke2fs")
-        .arg("-t")
-        .arg("ext4")
-        .arg("-d")
-        .arg(rootfs)
-        .arg(&disk_image)
-        .output();
-
-    match mke2fs_result {
-        Ok(output) => {
-            if output.status.success() {
-                veprintln!("Disk image created successfully with mke2fs");
-                // Verify the image has content by checking if we can list files
-                let verify = Command::new("debugfs")
-                    .arg("-R")
-                    .arg("ls -l /")
-                    .arg(&disk_image)
-                    .output();
-                if let Ok(v) = verify {
-                    veprintln!("Root directory contents:\n{}", String::from_utf8_lossy(&v.stdout));
-                }
-                return Ok(disk_image);
-            } else {
-                let stderr = String::from_utf8_lossy(&output.stderr);
-                let stdout = String::from_utf8_lossy(&output.stdout);
-                veprintln!("mke2fs failed!");
-                veprintln!("  stdout: {}", stdout);
-                veprintln!("  stderr: {}", stderr);
-                // Don't continue if mke2fs exists but failed - it's the only reliable method
-                return Err(anyhow!(
-                    "mke2fs -d failed to create disk image.\n\
-                     stdout: {}\n\
-                     stderr: {}",
-                    stdout, stderr
-                ));
-            }
-        }
-        Err(e) => {
-            veprintln!("mke2fs not available: {}", e);
-        }
-    }
-
-    // Fallback: create a simple ext4 image and copy files
-    // Try mkfs.ext4
-    let mkfs_result = Command::new("mkfs.ext4")
-        .arg("-F")
-        .arg(&disk_image)
-        .output();
-
-    match mkfs_result {
-        Ok(output) => {
-            if !output.status.success() {
-                return Err(anyhow!(
-                    "mkfs.ext4 failed: {}",
-                    String::from_utf8_lossy(&output.stderr)
-                ));
-            }
-        }
-        Err(e) => {
-            return Err(anyhow!(
-                "Neither mke2fs nor mkfs.ext4 available. Install e2fsprogs:\n\
-                 Ubuntu/Debian: sudo apt install e2fsprogs\n\
-                 Arch: sudo pacman -S e2fsprogs\n\
-                 Alpine: sudo apk add e2fsprogs\n\
-                 Error: {}",
-                e
-            ));
-        }
-    }
-
-    // Mount the image and copy files
-    veprintln!("Mounting disk image and copying files...");
-
-    // Use debugfs to copy files (doesn't require root/mount)
-    let debugfs_result = copy_with_debugfs(rootfs, &disk_image)?;
-
-    if debugfs_result {
-        veprintln!("Disk image created successfully");
-        return Ok(disk_image);
-    }
-
-    // If debugfs failed, we need to try mounting (requires root or fuse)
-    // This is a last resort
-    Err(anyhow!(
-        "Could not create disk image. Please ensure e2fsprogs is installed with mke2fs support.\n\
-         The mke2fs -d option is required for non-root disk image creation."
-    ))
 }
 
-/// Copy files to the disk image using debugfs
+/// Create a newc-format cpio archive from a directory using the cpio crate
-fn copy_with_debugfs(rootfs: &PathBuf, disk_image: &PathBuf) -> Result<bool> {
+fn create_cpio_archive(rootfs: &Path) -> Result<Vec<u8>> {
-    // Use debugfs to write files - this doesn't require mounting
+    let mut archive = Vec::new();
-    let mut debugfs = match Command::new("debugfs")
+    
-        .arg("-w")
+    // Collect all entries with their data
-        .arg(disk_image)
+    let entries = collect_entries(rootfs, rootfs)?;
-        .stdin(Stdio::piped())
+    
-        .stdout(Stdio::piped())
+    // Write each entry using the cpio crate
-        .stderr(Stdio::piped())
+    for (name, mode, mtime, nlink, data) in entries {
-        .spawn()
+        let file_size = data.len() as u32;
-    {
+        
-        Ok(child) => child,
+        let builder = NewcBuilder::new(&name)
-        Err(_) => return Ok(false),
+            .mode(mode)
+            .uid(0)
+            .gid(0)
+            .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)
+            .context("Failed to write file content to cpio archive")?;
+        
+        // Finish this entry (returns the underlying writer)
+        writer.finish()
+            .context("Failed to finish cpio entry")?;
+    }
+    
+    // Write the trailer (takes ownership and returns the writer)
+    archive = newc::trailer(archive)
+        .context("Failed to write cpio trailer")?;
+
+    Ok(archive)
+}
+
+/// Collect all filesystem entries recursively
+fn collect_entries(base: &Path, current: &Path) -> Result<Vec<(String, u32, u32, u32, Vec<u8>)>> {
+    let mut entries = Vec::new();
+    
+    // Read directory entries
+    let dir_entries: Vec<_> = match std::fs::read_dir(current) {
+        Ok(entries) => entries.collect::<std::result::Result<_, _>>()?,
+        Err(e) => {
+            veprintln!("Warning: cannot read directory {}: {}", current.display(), e);
+            return Ok(entries);
+        }
     };
     
-    let stdin = debugfs.stdin.as_mut().context("Failed to open debugfs stdin")?;
+    for entry in dir_entries {
-
-    // Write files recursively
-    fn write_directory(
-        dir: &PathBuf,
-        prefix: &str,
-        stdin: &mut std::process::ChildStdin,
-    ) -> Result<()> {
-        for entry in std::fs::read_dir(dir)? {
-            let entry = entry?;
         let path = entry.path();
-            let name = entry.file_name().to_string_lossy().into_owned();
+        
-            let target = if prefix.is_empty() {
+        // Get metadata
-                format!("/{}", name)
+        let metadata = match std::fs::symlink_metadata(&path) {
-            } else {
+            Ok(m) => m,
-                format!("{}/{}", prefix, name)
+            Err(e) => {
+                veprintln!("Warning: skipping {} due to metadata error: {}", path.display(), e);
+                continue;
+            }
         };
         
-            if path.is_dir() {
+        let file_type = metadata.file_type();
-                // Create directory
+        
-                writeln!(stdin, "mkdir {}", target)?;
+        // Determine mode (file type + permissions from filesystem)
-                write_directory(&path, &target, stdin)?;
+        let mode = if file_type.is_dir() {
+            // Directory: preserve permissions, ensure at least rwx for owner
+            0o040000 | (metadata.mode() & 0o7777)
+        } else if file_type.is_symlink() {
+            0o120777 // symlink with rwxrwxrwx (permissions don't matter for symlinks)
+        } else if file_type.is_file() {
+            // Regular file: preserve permissions from filesystem
+            0o100000 | (metadata.mode() & 0o7777)
         } else {
-                // Write file
+            continue; // Skip other types (sockets, fifos, etc.)
-                writeln!(stdin, "write {} {}", path.display(), target)?;
+        };
+        
+        // Get file content or symlink target
+        let data: Vec<u8> = if file_type.is_file() {
+            match std::fs::read(&path) {
+                Ok(data) => data,
+                Err(e) => {
+                    veprintln!("Warning: cannot read file {}: {}", path.display(), e);
+                    continue;
                 }
             }
-        Ok(())
+        } else if file_type.is_symlink() {
+            match std::fs::read_link(&path) {
+                Ok(target) => target.to_string_lossy().into_owned().into_bytes(),
+                Err(e) => {
+                    veprintln!("Warning: cannot read symlink {}: {}", path.display(), e);
+                    continue;
+                }
+            }
+        } else {
+            Vec::new()
+        };
+        
+        // Build the entry name (relative path from base)
+        let relative = path.strip_prefix(base).unwrap();
+        let entry_name = relative.to_string_lossy().into_owned();
+        
+        // nlink: directories have 2 (. and ..), files/symlinks have 1
+        let nlink = if file_type.is_dir() { 2 } else { 1 };
+        
+        entries.push((entry_name, mode, metadata.mtime() as u32, nlink, data));
+        
+        // Recurse into directories
+        if file_type.is_dir() {
+            let mut sub_entries = collect_entries(base, &path)?;
+            entries.append(&mut sub_entries);
+        }
     }
     
-    if let Err(e) = write_directory(rootfs, "", stdin) {
+    Ok(entries)
-        veprintln!("debugfs write failed: {}", e);
-        let _ = debugfs.kill();
-        return Ok(false);
-    }
-
-    // stdin is implicitly dropped here when it goes out of scope
-
-    let output = debugfs
-        .wait_with_output()
-        .context("Failed to wait for debugfs")?;
-
-    if !output.status.success() {
-        veprintln!(
-            "debugfs failed: {}",
-            String::from_utf8_lossy(&output.stderr)
-        );
-        return Ok(false);
-    }
-
-    Ok(true)
 }