factorize mounting read-only filesystems (squashfs, erofs)

src/cmd/init/bootstrap.rs

@@ -3,7 +3,7 @@ use log::{debug, info, warn};
 use std::path::{Path, PathBuf};
 use tokio::{
     fs,
-    io::{AsyncBufReadExt, AsyncReadExt, AsyncWrite, AsyncWriteExt, BufReader},
+    io::{AsyncBufReadExt, AsyncWrite, AsyncWriteExt, BufReader},
 };
 
 use dkl::{
@@ -13,7 +13,7 @@ use dkl::{
     bootstrap::Config,
 };
 
-use super::{exec, mount, retry, retry_or_ignore, try_exec, try_exec_cmd};
+use super::{exec, mount, mount_ro_fs, retry, retry_or_ignore, try_exec, try_exec_cmd};
 use crate::{fs::walk_dir, utils};
 
 pub async fn bootstrap(cfg: Config) {
@@ -340,25 +340,7 @@ impl LayerMounter<'_> {
             .await
         };
 
-        retry(async || {
-            let mut buf = [0u8; 1028];
-            fs::File::open(&mount_src)
-                .await
-                .map_err(|e| format_err!("open {}: {e}", mount_src.display()))?
-                .read_exact(&mut buf)
-                .await
-                .map_err(|e| format_err!("read {}: {e}", mount_src.display()))?;
-
-            let fstype = if buf[1024..1028] == 0xE0F5E1E2u32.to_le_bytes() {
-                "erofs"
-            } else {
-                "squashfs"
-            };
-
-            mount(Some(&mount_src), &tgt_dir, fstype, None).await;
-            Ok(())
-        })
-        .await;
+        retry(async || mount_ro_fs(&mount_src, &tgt_dir).await).await;
 
         if !self.lower_dir.is_empty() {
             self.lower_dir.push(':');