diff --git a/src/iter.rs b/src/iter.rs
index 0e0922e..2e34765 100644
--- a/src/iter.rs
+++ b/src/iter.rs
@@ -1,6 +1,5 @@
 use std::io::Read;
 
-use crate::fat::Fatty;
 use crate::subslice::SubSlice;
 use crate::utils::replace;
 use crate::{FatFs, SliceLike};
@@ -12,7 +11,7 @@ pub struct ClusterChainReader<'a, S: SliceLike> {
 }
 
 impl<'a, S: SliceLike> ClusterChainReader<'a, S> {
-    pub fn new(fat_fs: &'a mut FatFs<S>, first_cluster: u32) -> ClusterChainReader<'a, S> {
+    pub fn new(fat_fs: &'a FatFs<S>, first_cluster: u32) -> ClusterChainReader<'a, S> {
         let next_cluster = fat_fs.next_cluster(first_cluster).unwrap_or(None);
 
         let sub_slice = fat_fs.cluster_as_subslice(first_cluster);
diff --git a/src/lib.rs b/src/lib.rs
index e948f4b..a0f086c 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -1,4 +1,6 @@
-use std::io::{Read as _, Seek as _, SeekFrom, Write as _};
+use std::cell::RefCell;
+use std::io::{Read, Seek, SeekFrom, Write};
+use std::rc::Rc;
 
 use crate::dir::{DirIter, RegularDirEntry};
 use crate::fat::{FatError, Fatty};
@@ -94,7 +96,7 @@ impl SliceLike for std::fs::File {
 
 #[allow(dead_code)]
 pub struct FatFs<S: SliceLike> {
-    data: S,
+    inner: Rc<RefCell<S>>,
 
     fat_offset: u64,
     fat_size: usize,
@@ -150,8 +152,10 @@ impl<S: SliceLike> FatFs<S> {
 
         let bytes_per_cluster = bpb.bytes_per_cluster();
 
+        let data = Rc::new(RefCell::new(data));
+
         Ok(FatFs {
-            data,
+            inner: data,
             fat_offset,
             fat_size,
             root_dir_offset,
@@ -194,7 +198,7 @@ impl<S: SliceLike> FatFs<S> {
         SubSliceMut::new(self, offset, self.bytes_per_cluster)
     }
 
-    pub fn cluster_as_subslice(&mut self, cluster: u32) -> SubSlice<'_, S> {
+    pub fn cluster_as_subslice(&self, cluster: u32) -> SubSlice<'_, S> {
         let offset = self.data_cluster_to_offset(cluster);
 
         SubSlice::new(self, offset, self.bytes_per_cluster)
@@ -215,20 +219,20 @@ impl<S: SliceLike> FatFs<S> {
 
         let mut data = vec![0; self.bytes_per_cluster];
 
-        self.data
-            .read_at_offset(self.data_cluster_to_offset(cluster), &mut data)?;
+        let mut inner = self.inner.borrow_mut();
+
+        inner.read_at_offset(self.data_cluster_to_offset(cluster), &mut data)?;
 
         while let Ok(Some(next_cluster)) = self.next_cluster(cluster) {
             cluster = next_cluster;
 
-            self.data
-                .read_at_offset(self.data_cluster_to_offset(cluster), &mut data)?;
+            inner.read_at_offset(self.data_cluster_to_offset(cluster), &mut data)?;
         }
 
         Ok(data)
     }
 
-    pub fn root_dir_iter(&mut self) -> Box<dyn Iterator<Item = RegularDirEntry> + '_> {
+    pub fn root_dir_iter(&self) -> Box<dyn Iterator<Item = RegularDirEntry> + '_> {
         // TODO: maybe wrap this in another RootDirIter enum, so we don't have to Box<dyn>
 
         if let Some(root_dir_offset) = self.root_dir_offset {
@@ -248,4 +252,8 @@ impl<S: SliceLike> FatFs<S> {
 
         Box::new(DirIter::new(cluster_iter))
     }
+
+    pub fn chain_reader(&self, first_cluster: u32) -> impl Read {
+        iter::ClusterChainReader::new(self, first_cluster)
+    }
 }
diff --git a/src/subslice.rs b/src/subslice.rs
index 4dbb43c..821081c 100644
--- a/src/subslice.rs
+++ b/src/subslice.rs
@@ -44,7 +44,8 @@ impl<S: SliceLike> Read for SubSliceMut<'_, S> {
         let bytes_to_read = self.len.min(buf.len());
 
         self.fat_fs
-            .data
+            .inner
+            .borrow_mut()
             .read_at_offset(self.offset, &mut buf[..bytes_to_read])?;
 
         self.offset += bytes_to_read as u64;
@@ -59,7 +60,8 @@ impl<S: SliceLike> Write for SubSliceMut<'_, S> {
         let bytes_to_write = self.len.min(buf.len());
 
         self.fat_fs
-            .data
+            .inner
+            .borrow_mut()
             .write_at_offset(self.offset, &buf[..bytes_to_write])?;
 
         self.offset += bytes_to_write as u64;
@@ -74,7 +76,7 @@ impl<S: SliceLike> Write for SubSliceMut<'_, S> {
 }
 
 pub struct SubSlice<'a, S: SliceLike> {
-    fat_fs: &'a mut FatFs<S>,
+    fat_fs: &'a FatFs<S>,
 
     offset: u64,
     len: usize,
@@ -90,7 +92,7 @@ impl<S: SliceLike> Debug for SubSlice<'_, S> {
 }
 
 impl<S: SliceLike> SubSlice<'_, S> {
-    pub fn new(fat_fs: &mut FatFs<S>, offset: u64, len: usize) -> SubSlice<'_, S> {
+    pub fn new(fat_fs: &FatFs<S>, offset: u64, len: usize) -> SubSlice<'_, S> {
         SubSlice {
             fat_fs,
             offset,
@@ -115,7 +117,7 @@ impl<S: SliceLike> SubSlice<'_, S> {
 }
 
 impl<'a, S: SliceLike> SubSlice<'a, S> {
-    pub fn release(self) -> &'a mut FatFs<S> {
+    pub fn release(self) -> &'a FatFs<S> {
         self.fat_fs
     }
 }
@@ -125,7 +127,8 @@ impl<S: SliceLike> Read for SubSlice<'_, S> {
         let bytes_to_read = self.len.min(buf.len());
 
         self.fat_fs
-            .data
+            .inner
+            .borrow_mut()
             .read_at_offset(self.offset, &mut buf[..bytes_to_read])?;
 
         self.offset += bytes_to_read as u64;