Add readonly volume open function

Author: Murmele

src/volume_mgr.rs

@@ -102,11 +102,22 @@ where
     pub fn open_volume(
         &mut self,
         volume_idx: VolumeIdx,
-        read_only: bool,
     ) -> Result<Volume<D, T, MAX_DIRS, MAX_FILES, MAX_VOLUMES>, Error<D::Error>> {
         return self._open_volume(volume_idx, false);
     }
 
+    /// Get a read only volume (or partition) based on entries in the Master Boot Record.
+    /// Opening and closing a read only volume is faster than a writable volume.
+    ///
+    /// We do not support GUID Partition Table disks. Nor do we support any
+    /// concept of drive letters - that is for a higher layer to handle.
+    pub fn open_volume_read_only(
+        &mut self,
+        volume_idx: VolumeIdx,
+    ) -> Result<Volume<D, T, MAX_DIRS, MAX_FILES, MAX_VOLUMES>, Error<D::Error>> {
+        return self._open_volume(volume_idx, true);
+    }
+
     /// Get a volume (or partition) based on entries in the Master Boot Record.
     ///
     /// We do not support GUID Partition Table disks. Nor do we support any