Update FSInfo sector on unmount/drop

TODO.md

@@ -1,6 +1,5 @@
 TODO
 ====
-* FsInfo sector handling
 * move file API
 * format volume API
 * better no_std support

src/fs.rs

@@ -273,12 +273,14 @@ impl FsInfoSector {
 #[derive(Debug, Clone, Copy)]
 pub struct FsOptions {
     pub(crate) update_accessed_date: bool,
+    pub(crate) update_fs_info: bool,
 }
 
 impl FsOptions {
     pub fn new() -> Self {
         FsOptions {
             update_accessed_date: false,
+            update_fs_info: false,
         }
     }
 
@@ -287,6 +289,12 @@ impl FsOptions {
         self.update_accessed_date = enabled;
         self
     }
+
+    /// If enabled library updates FSInfo sector when unmounting
+    pub fn update_fs_info(mut self, enabled: bool) -> Self {
+        self.update_fs_info = enabled;
+        self
+    }
 }
 
 /// FAT filesystem statistics
@@ -493,6 +501,35 @@ impl <'a> FileSystem<'a> {
             free_clusters,
         })
     }
+
+    /// Unmounts filesystem. Updates FSInfo sector if required in options.
+    pub fn unmount(self) -> io::Result<()> {
+        self.unmount_internal()
+    }
+
+    fn unmount_internal(&self) -> io::Result<()> {
+        if self.options.update_fs_info {
+            self.flush_fs_info()?;
+        }
+        Ok(())
+    }
+
+    fn flush_fs_info(&self) -> io::Result<()> {
+        if self.fat_type == FatType::Fat32 {
+            let mut disk = self.disk.borrow_mut();
+            disk.seek(SeekFrom::Start(self.bpb.fs_info_sector as u64 * 512))?;
+            self.fs_info.borrow().serialize(&mut *disk)?;
+        }
+        Ok(())
+    }
+}
+
+impl<'a> Drop for FileSystem<'a> {
+    fn drop(&mut self) {
+        if let Err(err) = self.unmount_internal() {
+            error!("unmount failed {}", err);
+        }
+    }
 }
 
 #[derive(Clone)]

tests/write.rs

@@ -24,7 +24,7 @@ fn call_with_fs(f: &Fn(FileSystem) -> (), filename: &str, test_seq: u32) {
     {
         let file = fs::OpenOptions::new().read(true).write(true).open(&tmp_path).unwrap();
         let mut buf_file = BufStream::new(file);
-        let options = FsOptions::new().update_accessed_date(true);
+        let options = FsOptions::new().update_accessed_date(true).update_fs_info(true);
         let fs = FileSystem::new(&mut buf_file, options).unwrap();
         f(fs);
     }