fix: clear directory returned from create_dir method

Previous implementation did not zero allocated cluster so created directory
could have garbage contents.
Bug exists in code since version 0.2 and all code using create_dir is
affected.
This commit also improves tests of volume formatting so a dirty partition
is used allowing to detect bugs like this.

src/dir.rs

@@ -236,7 +236,7 @@ impl<'a, T: ReadWriteSeek + 'a> Dir<'a, T> {
             // directory does not exist - create it
             DirEntryOrShortName::ShortName(short_name) => {
                 // alloc cluster for directory data
-                let cluster = self.fs.alloc_cluster(None)?;
+                let cluster = self.fs.alloc_cluster(None, true)?;
                 // create entry in parent directory
                 let sfn_entry = self.create_sfn_entry(short_name, FileAttributes::DIRECTORY, Some(cluster));
                 let entry = self.write_entry(name, sfn_entry)?;

src/file.rs

@@ -261,22 +261,11 @@ impl<'a, T: ReadWriteSeek> Write for File<'a, T> {
                 Some(n) => n,
                 None => {
                     // end of chain reached - allocate new cluster
-                    let new_cluster = self.fs.alloc_cluster(self.current_cluster)?;
+                    let new_cluster = self.fs.alloc_cluster(self.current_cluster, self.is_dir())?;
                     trace!("allocated cluser {}", new_cluster);
                     if self.first_cluster.is_none() {
                         self.set_first_cluster(new_cluster);
                     }
-                    if self.is_dir() {
-                        // zero new directory cluster
-                        trace!("zeroing directory cluster {}", new_cluster);
-                        let abs_pos = self.fs.offset_from_cluster(new_cluster);
-                        let mut disk = self.fs.disk.borrow_mut();
-                        disk.seek(SeekFrom::Start(abs_pos))?;
-                        for _ in 0..cluster_size / 32 {
-                            let zero = [0u8; 32];
-                            disk.write(&zero)?;
-                        }
-                    }
                     new_cluster
                 },
             }

src/fs.rs

@@ -472,11 +472,18 @@ impl<T: ReadWriteSeek> FileSystem<T> {
         Ok(())
     }
 
-    pub(crate) fn alloc_cluster(&self, prev_cluster: Option<u32>) -> io::Result<u32> {
+    pub(crate) fn alloc_cluster(&self, prev_cluster: Option<u32>, zero: bool) -> io::Result<u32> {
         trace!("alloc_cluster");
         let hint = self.fs_info.borrow().next_free_cluster;
+        let cluster = {
             let mut fat = self.fat_slice();
-        let cluster = alloc_cluster(&mut fat, self.fat_type, prev_cluster, hint, self.total_clusters)?;
+            alloc_cluster(&mut fat, self.fat_type, prev_cluster, hint, self.total_clusters)?
+        };
+        if zero {
+            let mut disk = self.disk.borrow_mut();
+            disk.seek(SeekFrom::Start(self.offset_from_cluster(cluster)))?;
+            write_zeros(&mut *disk, self.cluster_size() as usize)?;
+        }
         let mut fs_info = self.fs_info.borrow_mut();
         fs_info.set_next_free_cluster(cluster + 1);
         fs_info.add_free_clusters(-1);

tests/format.rs

@@ -50,7 +50,8 @@ fn basic_fs_test(fs: &FileSystem) {
 
 fn test_format_fs(opts: fatfs::FormatVolumeOptions, total_bytes: u64) -> FileSystem {
     let _ = env_logger::try_init();
-    let storage_vec: Vec<u8> = Vec::with_capacity(total_bytes as usize);
+    // Init storage to 0xD1 bytes (value has been choosen to be parsed as normal file)
+    let storage_vec: Vec<u8> = vec![0xD1u8; total_bytes as usize];
     let storage_cur = io::Cursor::new(storage_vec);
     let mut buffered_stream = BufStream::new(storage_cur);
     fatfs::format_volume(&mut buffered_stream, opts).expect("format volume");
@@ -86,7 +87,7 @@ fn test_format_50mb() {
 
 
 #[test]
-fn test_format_512mb() {
+fn test_format_512mb_512sec() {
     let total_bytes = 2 * 1024 * MB;
     let opts = fatfs::FormatVolumeOptions::new((total_bytes / 512) as u32, 512);
     let fs = test_format_fs(opts, total_bytes);