factorize mounting read-only filesystems (squashfs, erofs)

src/cmd/init.rs

@@ -4,7 +4,7 @@ use std::collections::BTreeSet as Set;
 use std::convert::Infallible;
 use std::os::unix::fs::symlink;
 use tokio::sync::Mutex;
-use tokio::{fs, process::Command};
+use tokio::{fs, io::AsyncReadExt, process::Command};
 
 use crate::{cmd::version::version_string, dklog, input, utils};
 use dkl::bootstrap::Config;
@@ -154,7 +154,8 @@ use std::path::Path;
 
 async fn mount_modules(modules: &str, kernel_version: &str) -> Result<()> {
     info!("mounting modules");
-    mount(Some(modules), "/modules", "squashfs", None).await;
+
+    mount_ro_fs(modules, "/modules").await?;
 
     fs::create_dir_all("/lib/modules").await?;
     let modules_path = &format!("/modules/lib/modules/{kernel_version}");
@@ -243,6 +244,35 @@ async fn mount<S: AsRef<Path>>(
     .await
 }
 
+async fn mount_ro_fs(src: impl AsRef<Path>, dst: impl AsRef<Path>) -> Result<()> {
+    let src = src.as_ref();
+    let dst = dst.as_ref();
+
+    // identify RO fs type
+    let mut buf = [0u8; 1028];
+
+    fs::File::open(src)
+        .await
+        .map_err(|e| format_err!("open {}: {e}", src.display()))?
+        .read_exact(&mut buf)
+        .await
+        .map_err(|e| format_err!("read {}: {e}", src.display()))?;
+
+    let fstype = if buf[1024..1028] == 0xE0F5E1E2u32.to_le_bytes() {
+        "erofs"
+    } else {
+        "squashfs"
+    };
+
+    if let Err(e) = fs::create_dir_all(dst).await {
+        error!("failed to create dir {dst}: {e}", dst = dst.display());
+    }
+
+    let mut cmd = Command::new("mount");
+    cmd.args(["-t", fstype]).arg(src).arg(dst);
+    try_exec_cmd(cmd).await
+}
+
 async fn start_daemon(prog: &str, args: &[&str]) {
     let (cmd_str, mut cmd) = cmd_str(prog, args);
     retry_or_ignore(async || {
@@ -253,7 +283,7 @@ async fn start_daemon(prog: &str, args: &[&str]) {
     .await;
 }
 
-async fn try_exec_cmd(mut cmd: tokio::process::Command) -> Result<()> {
+async fn try_exec_cmd(mut cmd: Command) -> Result<()> {
     info!(
         "# {} {}",
         cmd.as_std().get_program().to_string_lossy(),