virtme-ng-init: overlayfs: fall back to mounting without xino option

Older kernels don't support the 'xino' overlayfs mount option so we end
up with no overlay mounts. Fall back to mounting without that option to
work around that. It's not pretty as we end up with errors like:

[ 0.380206] overlayfs: unrecognized mount option "xino=off" or missing value
[ 0.383246] overlayfs: unrecognized mount option "xino=off" or missing value

Apply to virtme-ng-init the same change applied by Juerg in virtme-init.

Link: arighi/virtme-ng#124
Reported-by: Juerg Haefliger <juergh@proton.me>
Signed-off-by: Andrea Righi <andrea.righi@canonical.com>

src/main.rs

@@ -452,7 +452,15 @@ fn mount_virtme_overlays() {
             utils::do_mkdir(dir);
             utils::do_mkdir(upperdir);
             utils::do_mkdir(workdir);
-            utils::do_mount(&key, &path, "overlay", 0, mnt_opts);
+            let result = utils::do_mount_check(&key, &path, "overlay", 0, mnt_opts);
+            if let Err(_) = result {
+                // Old kernels don't support xino=on|off, re-try without this option.
+                let mnt_opts = &format!(
+                    "lowerdir={},upperdir={},workdir={}",
+                    path, upperdir, workdir
+                );
+                utils::do_mount(&key, &path, "overlay", 0, mnt_opts);
+            }
         }
     }
 }

src/utils.rs

@@ -112,7 +112,13 @@ pub fn do_symlink(src: &str, dst: &str) {
     }
 }
 
-pub fn do_mount(source: &str, target: &str, fstype: &str, flags: usize, fsdata: &str) {
+pub fn do_mount_check(
+    source: &str,
+    target: &str,
+    fstype: &str,
+    flags: usize,
+    fsdata: &str,
+) -> Result<(), nix::Error> {
     let source_cstr = CString::new(source).expect("CString::new failed");
     let fstype_cstr = CString::new(fstype).expect("CString::new failed");
     let fsdata_cstr = CString::new(fsdata).expect("CString::new failed");
@@ -124,6 +130,12 @@ pub fn do_mount(source: &str, target: &str, fstype: &str, flags: usize, fsdata:
         MsFlags::from_bits_truncate(flags.try_into().unwrap()),
         Some(fsdata_cstr.as_ref()),
     );
+
+    result
+}
+
+pub fn do_mount(source: &str, target: &str, fstype: &str, flags: usize, fsdata: &str) {
+    let result = do_mount_check(source, target, fstype, flags, fsdata);
     if let Err(err) = result {
         if err != nix::errno::Errno::ENOENT {
             log!("mount {} -> {}: {}", source, target, err);