Alloc and free clusters for file data.

README.md

@@ -6,16 +6,20 @@ Rust FAT
 Introduction
 ------------
 
-FAT filesystem read-only library implemented in Rust.
+FAT filesystem library implemented in Rust.
 
 Features:
-* FAT12, FAT16, FAT32 filesystem versions,
+* FAT12, FAT16, FAT32 supported,
-* read directory,
+* read directory entries,
-* read file,
+* read file contents,
-* LFN (Long File Names).
+* LFN (Long File Names),
+* basic write support (write and truncate existing file).
 
-Planned features:
+Missing features (yet):
-* write support,
+* create new file/directory,
+* remove file/directory,
+
+Other planned features (Nice to Have):
 * no_std environment support.
 
 License

src/dir.rs

@@ -83,6 +83,12 @@ impl DirFileEntryData {
         if n == 0 { None } else { Some(n) }
     }
     
+    pub(crate) fn set_first_cluster(&mut self, cluster: Option<u32>) {
+        let n = cluster.unwrap_or(0);
+        self.first_cluster_hi = (n >> 16) as u16;
+        self.first_cluster_lo = (n & 0xFFFF) as u16;
+    }
+    
     pub(crate) fn size(&self) -> u32 {
         self.size
     }
@@ -372,10 +378,8 @@ pub struct DirIter<'a, 'b: 'a> {
 
 impl <'a, 'b> DirIter<'a, 'b> {
     fn read_dir_entry_data(&mut self) -> io::Result<DirEntryData> {
-        println!("read_dir_entry_data");
         let mut name = [0; 11];
         self.rdr.read_exact(&mut name)?;
-        println!("read_dir_entry_data {:?}", &name);
         let attrs = FileAttributes::from_bits_truncate(self.rdr.read_u8()?);
         if attrs == FileAttributes::LFN {
             let mut data = DirLfnEntryData {
@@ -389,7 +393,6 @@ impl <'a, 'b> DirIter<'a, 'b> {
             self.rdr.read_u16_into::<LittleEndian>(&mut data.name_1)?;
             data.reserved_0 = self.rdr.read_u16::<LittleEndian>()?;
             self.rdr.read_u16_into::<LittleEndian>(&mut data.name_2)?;
-            println!("read_dir_entry_data end");
             Ok(DirEntryData::Lfn(data))
         } else {
             let data = DirFileEntryData {
@@ -406,12 +409,13 @@ impl <'a, 'b> DirIter<'a, 'b> {
                 first_cluster_lo: self.rdr.read_u16::<LittleEndian>()?,
                 size:             self.rdr.read_u32::<LittleEndian>()?,
             };
-            println!("read_dir_entry_data end");
             Ok(DirEntryData::File(data))
         }
     }
 }
 
+const DIR_ENTRY_SIZE: u64 = 32;
+
 impl <'a, 'b> Iterator for DirIter<'a, 'b> {
     type Item = io::Result<DirEntry<'a, 'b>>;
 
@@ -421,8 +425,8 @@ impl <'a, 'b> Iterator for DirIter<'a, 'b> {
         }
         let mut lfn_buf = Vec::<u16>::new();
         loop {
-            let entry_pos = self.rdr.global_pos();
             let res = self.read_dir_entry_data();
+            let entry_pos = self.rdr.global_pos().map(|p| p - DIR_ENTRY_SIZE);
             let data = match res {
                 Ok(data) => data,
                 Err(err) => {

src/file.rs

@@ -9,6 +9,7 @@ use dir::{FileEntryInfo, DateTime};
 #[derive(Clone)]
 pub struct File<'a, 'b: 'a> {
     first_cluster: Option<u32>,
+    // Note: if offset points between clusters current_cluster is the previous cluster
     current_cluster: Option<u32>,
     offset: u32,
     entry: Option<FileEntryInfo>,
@@ -20,7 +21,7 @@ impl <'a, 'b> File<'a, 'b> {
     pub(crate) fn new(first_cluster: Option<u32>, entry: Option<FileEntryInfo>, fs: FileSystemRef<'a, 'b>) -> Self {
         File {
             first_cluster, entry, fs,
-            current_cluster: first_cluster,
+            current_cluster: None, // cluster before first one
             offset: 0,
             entry_dirty: false,
         }
@@ -38,20 +39,32 @@ impl <'a, 'b> File<'a, 'b> {
         }
     }
     
-    pub fn truncate(&mut self) {
+    pub fn truncate(&mut self) -> io::Result<()> {
-        // FIXME: free clusters?
         match self.entry {
             Some(ref mut e) => {
-                if e.data.size != self.offset {
+                if e.data.size == self.offset {
-                    e.data.size = self.offset;
+                    return Ok(());
-                    self.entry_dirty = true;
                 }
+                
+                e.data.size = self.offset;
+                if self.offset == 0 {
+                    e.data.set_first_cluster(None);
+                }
+                self.entry_dirty = true;
             },
             _ => {},
         }
+        if self.offset > 0 {
+            self.fs.cluster_iter(self.current_cluster.unwrap()).truncate()
+        } else {
+            self.fs.cluster_iter(self.first_cluster.unwrap()).free()?;
+            self.first_cluster = None;
+            Ok(())
+        }
     }
     
     pub(crate) fn global_pos(&self) -> Option<u64> {
+        // Note: when between clusters it returns position after previous cluster
         match self.current_cluster {
             Some(n) => {
                 let cluster_size = self.fs.get_cluster_size();
@@ -93,6 +106,17 @@ impl <'a, 'b> File<'a, 'b> {
             None => None,
         }
     }
+    
+    fn set_first_cluster(&mut self, cluster: u32) {
+        self.first_cluster = Some(cluster);
+        match self.entry {
+            Some(ref mut e) => {
+                e.data.set_first_cluster(self.first_cluster);
+            },
+            None => {},
+        }
+        self.entry_dirty = true;
+    }
 }
 
 impl<'a, 'b> Drop for File<'a, 'b> {
@@ -106,7 +130,23 @@ impl<'a, 'b> Read for File<'a, 'b> {
         let mut buf_offset: usize = 0;
         let cluster_size = self.fs.get_cluster_size();
         loop {
-            let current_cluster = match self.current_cluster {
+            let current_cluster_opt = if self.offset % cluster_size == 0 {
+                // next cluster
+                match self.current_cluster {
+                    None => self.first_cluster,
+                    Some(n) => {
+                        let r = self.fs.cluster_iter(n).next();
+                        match r {
+                            Some(Err(err)) => return Err(err),
+                            Some(Ok(n)) => Some(n),
+                            None => None,
+                        }
+                    },
+                }
+            } else {
+                self.current_cluster
+            };
+            let current_cluster = match current_cluster_opt {
                 Some(n) => n,
                 None => break,
             };
@@ -118,6 +158,7 @@ impl<'a, 'b> Read for File<'a, 'b> {
             if read_size == 0 {
                 break;
             }
+            //println!("read c {} n {}", current_cluster, read_size);
             let offset_in_fs = self.fs.offset_from_cluster(current_cluster) + (offset_in_cluster as u64);
             let read_bytes = {
                 let mut disk = self.fs.disk.borrow_mut();
@@ -128,15 +169,8 @@ impl<'a, 'b> Read for File<'a, 'b> {
                 break;
             }
             self.offset += read_bytes as u32;
+            self.current_cluster = Some(current_cluster);
             buf_offset += read_bytes;
-            if self.offset % cluster_size == 0 {
-                let r = self.fs.cluster_iter(current_cluster).skip(1).next();
-                self.current_cluster = match r {
-                    Some(Err(err)) => return Err(err),
-                    Some(Ok(n)) => Some(n),
-                    None => None,
-                };
-            }
         }
         Ok(buf_offset)
     }
@@ -147,17 +181,45 @@ impl<'a, 'b> Write for File<'a, 'b> {
         let mut buf_offset: usize = 0;
         let cluster_size = self.fs.get_cluster_size();
         loop {
-            let current_cluster = match self.current_cluster {
-                Some(n) => n,
-                None => unimplemented!(), // FIXME: allocate cluster
-            };
             let offset_in_cluster = self.offset % cluster_size;
             let bytes_left_in_cluster = (cluster_size - offset_in_cluster) as usize;
             let bytes_left_in_buf = buf.len() - buf_offset;
             let write_size = cmp::min(bytes_left_in_buf, bytes_left_in_cluster);
+            //println!("write {:?}", write_size);
             if write_size == 0 {
                 break;
             }
+            
+            let current_cluster_opt = if self.offset % cluster_size == 0 {
+                // next cluster
+                let next_cluster = match self.current_cluster {
+                    None => self.first_cluster,
+                    Some(n) => {
+                        let r = self.fs.cluster_iter(n).next();
+                        match r {
+                            Some(Err(err)) => return Err(err),
+                            Some(Ok(n)) => Some(n),
+                            None => None,
+                        }
+                    },
+                };
+                match next_cluster {
+                    Some(_) => next_cluster,
+                    None => {
+                        let new_cluster = self.fs.alloc_cluster(self.current_cluster)?;
+                        if self.first_cluster.is_none() {
+                            self.set_first_cluster(new_cluster);
+                        }
+                        Some(new_cluster)
+                    },
+                }
+            } else {
+                self.current_cluster
+            };
+            let current_cluster = match current_cluster_opt {
+                Some(n) => n,
+                None => panic!("Offset inside cluster but no cluster allocated"), // FIXME
+            };
             let offset_in_fs = self.fs.offset_from_cluster(current_cluster) + (offset_in_cluster as u64);
             let written_bytes = {
                 let mut disk = self.fs.disk.borrow_mut();
@@ -168,15 +230,8 @@ impl<'a, 'b> Write for File<'a, 'b> {
                 break;
             }
             self.offset += written_bytes as u32;
+            self.current_cluster = Some(current_cluster);
             buf_offset += written_bytes;
-            if self.offset % cluster_size == 0 {
-                let r = self.fs.cluster_iter(current_cluster).skip(1).next();
-                self.current_cluster = match r {
-                    Some(Err(err)) => return Err(err),
-                    Some(Ok(n)) => Some(n),
-                    None => None,
-                };
-            }
         }
         self.update_size();
         Ok(buf_offset)
@@ -200,11 +255,15 @@ impl<'a, 'b> Seek for File<'a, 'b> {
             return Err(io::Error::new(ErrorKind::InvalidInput, "invalid seek"));
         }
         let cluster_size = self.fs.get_cluster_size();
-        let cluster_count = (new_offset / cluster_size as i64) as usize;
+        let cluster_count = ((new_offset + cluster_size as i64 - 1) / cluster_size as i64 - 1) as isize;
-        let new_cluster = if cluster_count > 0 {
+        let new_cluster = if cluster_count == -1 {
+            None
+        } else if cluster_count == 0 {
+            self.first_cluster
+        } else {
             match self.first_cluster {
                 Some(n) => {
-                    match self.fs.cluster_iter(n).skip(cluster_count).next() {
+                    match self.fs.cluster_iter(n).skip(cluster_count as usize - 1).next() {
                         Some(Err(err)) => return Err(err),
                         Some(Ok(n)) => Some(n),
                         None => None,
@@ -212,8 +271,6 @@ impl<'a, 'b> Seek for File<'a, 'b> {
                 },
                 None => None,
             }
-        } else {
-            self.first_cluster
         };
         self.offset = new_offset as u32;
         self.current_cluster = new_cluster;

src/fs.rs

@@ -1,6 +1,5 @@
 use core::cell::RefCell;
 use core::cmp;
-use core::iter;
 use std::io::prelude::*;
 use std::io::{Error, ErrorKind, SeekFrom};
 use std::io;
@@ -8,7 +7,7 @@ use byteorder::{LittleEndian, ReadBytesExt};
 
 use file::File;
 use dir::{DirRawStream, Dir};
-use table::ClusterIterator;
+use table::{ClusterIterator, alloc_cluster};
 
 // FAT implementation based on:
 //   http://wiki.osdev.org/FAT
@@ -92,7 +91,6 @@ impl <'a> FileSystem<'a> {
     
     pub fn new<T: ReadWriteSeek>(disk: &'a mut T) -> io::Result<FileSystem<'a>> {
         let boot = Self::read_boot_record(disk)?;
-        println!("sig {:?}", boot.boot_sig);
         if boot.boot_sig != [0x55, 0xAA] {
             return Err(Error::new(ErrorKind::Other, "invalid signature"));
         }
@@ -218,16 +216,25 @@ impl <'a> FileSystem<'a> {
         self.offset_from_sector(self.sector_from_cluster(cluser))
     }
     
-    pub(crate) fn cluster_iter<'b>(&'b self, cluster: u32) -> iter::Chain<iter::Once<io::Result<u32>>, ClusterIterator<'b, 'a>> {
+    fn fat_slice<'b>(&'b self) -> DiskSlice<'b, 'a> {
         let bytes_per_sector = self.boot.bpb.bytes_per_sector as u64;
         let fat_offset = self.boot.bpb.reserved_sectors as u64 * bytes_per_sector;
         let sectors_per_fat =
             if self.boot.bpb.sectors_per_fat_16 == 0 { self.boot.bpb.sectors_per_fat_32 }
             else { self.boot.bpb.sectors_per_fat_16 as u32 };
         let fat_size = sectors_per_fat as u64 * bytes_per_sector;
-        let disk_slice = DiskSlice::new(fat_offset, fat_size, self);
+        DiskSlice::new(fat_offset, fat_size, self)
+    }
+    
+    pub(crate) fn cluster_iter<'b>(&'b self, cluster: u32) -> ClusterIterator<'b, 'a> {
+        let disk_slice = self.fat_slice();
         ClusterIterator::new(disk_slice, self.fat_type, cluster)
     }
+    
+    pub(crate) fn alloc_cluster(&self, prev_cluster: Option<u32>) -> io::Result<u32> {
+        let mut disk_slice = self.fat_slice();
+        alloc_cluster(&mut disk_slice, self.fat_type, prev_cluster)
+    }
 }
 
 #[derive(Clone)]

src/table.rs

@@ -1,72 +1,248 @@
 use std::io;
-use byteorder::{LittleEndian, ReadBytesExt};
+use std::io::prelude::*;
+use byteorder::{LittleEndian, ReadBytesExt, WriteBytesExt};
 use fs::{FatType, DiskSlice, ReadSeek};
-use core::iter;
 
-fn get_next_cluster(rdr: &mut ReadSeek, fat_type: FatType, cluster: u32) -> io::Result<Option<u32>> {
+struct Fat<T> {
+    #[allow(dead_code)]
+    dummy: [T; 0],
+}
+
+type Fat12 = Fat<u8>;
+type Fat16 = Fat<u16>;
+type Fat32 = Fat<u32>;
+
+#[derive(Debug, Clone, Copy)]
+enum FatValue {
+    Free,
+    Data(u32),
+    Bad,
+    EndOfChain,
+}
+
+trait FatTrait {
+    fn get(fat: &mut ReadSeek, cluster: u32) -> io::Result<FatValue>;
+    fn set(fat: &mut DiskSlice, cluster: u32, value: FatValue) -> io::Result<()>;
+    fn find_free(fat: &mut ReadSeek, hint_cluster: u32) -> io::Result<u32>;
+}
+
+fn read_fat(fat: &mut ReadSeek, fat_type: FatType, cluster: u32) -> io::Result<FatValue> {
     match fat_type {
-        FatType::Fat12 => get_next_cluster_12(rdr, cluster),
+        FatType::Fat12 => Fat12::get(fat, cluster),
-        FatType::Fat16 => get_next_cluster_16(rdr, cluster),
+        FatType::Fat16 => Fat16::get(fat, cluster),
-        FatType::Fat32 => get_next_cluster_32(rdr, cluster),
+        FatType::Fat32 => Fat32::get(fat, cluster),
     }
 }
 
-fn get_next_cluster_12(rdr: &mut ReadSeek, cluster: u32) -> io::Result<Option<u32>> {
+fn write_fat(fat: &mut DiskSlice, fat_type: FatType, cluster: u32, value: FatValue) -> io::Result<()> {
+    //println!("write_fat {} {:?}", cluster, value);
+    match fat_type {
+        FatType::Fat12 => Fat12::set(fat, cluster, value),
+        FatType::Fat16 => Fat16::set(fat, cluster, value),
+        FatType::Fat32 => Fat32::set(fat, cluster, value),
+    }
+}
+
+fn get_next_cluster(fat: &mut ReadSeek, fat_type: FatType, cluster: u32) -> io::Result<Option<u32>> {
+    let val = read_fat(fat, fat_type, cluster)?;
+    match val {
+        FatValue::Data(n) => Ok(Some(n)),
+        _ => Ok(None),
+    }
+}
+
+fn find_free_cluster(fat: &mut ReadSeek, fat_type: FatType, cluster: u32) -> io::Result<u32> {
+    match fat_type {
+        FatType::Fat12 => Fat12::find_free(fat, cluster),
+        FatType::Fat16 => Fat16::find_free(fat, cluster),
+        FatType::Fat32 => Fat32::find_free(fat, cluster),
+    }
+}
+
+pub(crate) fn alloc_cluster(fat: &mut DiskSlice, fat_type: FatType, prev_cluster: Option<u32>) -> io::Result<u32> {
+    let new_cluster = find_free_cluster(fat, fat_type, 2)?;
+    write_fat(fat, fat_type, new_cluster, FatValue::EndOfChain)?;
+    if prev_cluster.is_some() {
+        write_fat(fat, fat_type, prev_cluster.unwrap(), FatValue::Data(new_cluster))?; // safe
+    }
+    //println!("alloc_cluster {}", new_cluster);
+    Ok(new_cluster)
+}
+
+impl FatTrait for Fat12 {
+    fn get(fat: &mut ReadSeek, cluster: u32) -> io::Result<FatValue> {
         let fat_offset = cluster + (cluster / 2);
-    let mut bytes = [0;2];
+        fat.seek(io::SeekFrom::Start(fat_offset as u64))?;
-    rdr.seek(io::SeekFrom::Start(fat_offset as u64))?;
+        let packed_val = fat.read_u16::<LittleEndian>()?;
-    rdr.read(&mut bytes)?;
+        let val = match cluster & 1 {
-    let (val1, val2) = (bytes[0] as u16, bytes[1] as u16);
+            0 => packed_val & 0x0FFF,
-    
+            _ => packed_val >> 4,
-    let val = if cluster & 1 == 1 {
-        (val1 >> 4) | (val2 << 4)
-    } else {
-        val1 | (val2 & 0x0F)
         };
-    if val <= 1 || val >= 0xFF7 {
+        Ok(match val {
-        Ok(None)
+            0 => FatValue::Free,
-    } else {
+            0xFF7 => FatValue::Bad,
-        Ok(Some(val as u32))
+            0xFF8...0xFFF => FatValue::EndOfChain,
+            n => FatValue::Data(n as u32),
+        })
+    }
+    
+    fn set(fat: &mut DiskSlice, cluster: u32, value: FatValue) -> io::Result<()> {
+        let raw_val = match value {
+            FatValue::Free => 0,
+            FatValue::Bad => 0xFF7,
+            FatValue::EndOfChain => 0xFFF,
+            FatValue::Data(n) => n as u16,
+        };
+        let fat_offset = cluster + (cluster / 2);
+        fat.seek(io::SeekFrom::Start(fat_offset as u64))?;
+        let old_packed = fat.read_u16::<LittleEndian>()?;
+        fat.seek(io::SeekFrom::Start(fat_offset as u64))?;
+        let new_packed = match cluster & 1 {
+            0 => (old_packed & 0xF000) | raw_val,
+            _ => (old_packed & 0x000F) | (raw_val << 4),
+        };
+        fat.write_u16::<LittleEndian>(new_packed)?;
+        Ok(())
+    }
+
+    fn find_free(fat: &mut ReadSeek, hint_cluster: u32) -> io::Result<u32> {
+        let mut cluster = hint_cluster;
+        let fat_offset = cluster + (cluster / 2);
+        fat.seek(io::SeekFrom::Start(fat_offset as u64))?;
+        let mut packed_val = fat.read_u16::<LittleEndian>()?;
+        loop {
+            let val = match cluster & 1 {
+                0 => packed_val & 0x0FFF,
+                _ => packed_val >> 4,
+            };
+            if val == 0 {
+                return Ok(cluster);
+            }
+            cluster += 1;
+            packed_val = match cluster & 1 {
+                0 => fat.read_u16::<LittleEndian>()?,
+                _ => {
+                    let next_byte = fat.read_u8()? as u16;
+                    (packed_val >> 8) | (next_byte << 8)
+                },
+            };
+        }
     }
 }
 
-fn get_next_cluster_16(rdr: &mut ReadSeek, cluster: u32) -> io::Result<Option<u32>> {
+impl FatTrait for Fat16 {
-    rdr.seek(io::SeekFrom::Start((cluster*2) as u64))?;
+    fn get(fat: &mut ReadSeek, cluster: u32) -> io::Result<FatValue> {
-    let val = rdr.read_u16::<LittleEndian>()?;
+        fat.seek(io::SeekFrom::Start((cluster*2) as u64))?;
-    if val <= 1 || val >= 0xFFF7 {
+        let val = fat.read_u16::<LittleEndian>()?;
-        Ok(None)
+        Ok(match val {
-    } else {
+            0 => FatValue::Free,
-        Ok(Some(val as u32))
+            0xFFF7 => FatValue::Bad,
+            0xFFF8...0xFFFF => FatValue::EndOfChain,
+            n => FatValue::Data(n as u32),
+        })
+    }
+    
+    fn set(fat: &mut DiskSlice, cluster: u32, value: FatValue) -> io::Result<()> {
+        fat.seek(io::SeekFrom::Start((cluster*2) as u64))?;
+        let raw_val = match value {
+            FatValue::Free => 0,
+            FatValue::Bad => 0xFFF7,
+            FatValue::EndOfChain => 0xFFFF,
+            FatValue::Data(n) => n as u16,
+        };
+        fat.write_u16::<LittleEndian>(raw_val)?;
+        Ok(())
+    }
+    
+    fn find_free(fat: &mut ReadSeek, hint_cluster: u32) -> io::Result<u32> {
+        let mut cluster = hint_cluster;
+        fat.seek(io::SeekFrom::Start((cluster*2) as u64))?;
+        loop {
+            let val = fat.read_u16::<LittleEndian>()?;
+            if val == 0 {
+                return Ok(cluster);
+            }
+            cluster += 1;
+        }
     }
 }
 
-fn get_next_cluster_32(rdr: &mut ReadSeek, cluster: u32) -> io::Result<Option<u32>> {
+impl FatTrait for Fat32 {
-    rdr.seek(io::SeekFrom::Start((cluster*4) as u64))?;
+    fn get(fat: &mut ReadSeek, cluster: u32) -> io::Result<FatValue> {
-    let val = rdr.read_u32::<LittleEndian>()? & 0x0FFFFFFF;
+        fat.seek(io::SeekFrom::Start((cluster*4) as u64))?;
-    if val <= 1 || val >= 0x0FFFFFF7 {
+        let val = fat.read_u32::<LittleEndian>()? & 0x0FFFFFFF;
-        Ok(None)
+        Ok(match val {
-    } else {
+            0 => FatValue::Free,
-        Ok(Some(val))
+            0x0FFFFFF7 => FatValue::Bad,
+            0x0FFFFFF8...0x0FFFFFFF => FatValue::EndOfChain,
+            n => FatValue::Data(n as u32),
+        })
+    }
+    
+    fn set(fat: &mut DiskSlice, cluster: u32, value: FatValue) -> io::Result<()> {
+        fat.seek(io::SeekFrom::Start((cluster*4) as u64))?;
+        let raw_val = match value {
+            FatValue::Free => 0,
+            FatValue::Bad => 0x0FFFFFF7,
+            FatValue::EndOfChain => 0x0FFFFFFF,
+            FatValue::Data(n) => n,
+        };
+        fat.write_u32::<LittleEndian>(raw_val)?;
+        Ok(())
+    }
+    
+    fn find_free(fat: &mut ReadSeek, hint_cluster: u32) -> io::Result<u32> {
+        let mut cluster = hint_cluster;
+        fat.seek(io::SeekFrom::Start((cluster*4) as u64))?;
+        loop {
+            let val = fat.read_u32::<LittleEndian>()? & 0x0FFFFFFF;
+            if val == 0 {
+                return Ok(cluster);
+            }
+            cluster += 1;
+        }
     }
 }
 
 pub(crate) struct ClusterIterator<'a, 'b: 'a> {
-    rdr: DiskSlice<'a, 'b>,
+    fat: DiskSlice<'a, 'b>,
     fat_type: FatType,
     cluster: Option<u32>,
     err: bool,
 }
 
 impl <'a, 'b> ClusterIterator<'a, 'b> {
-    pub(crate) fn new(rdr: DiskSlice<'a, 'b>, fat_type: FatType, cluster: u32)
+    pub(crate) fn new(fat: DiskSlice<'a, 'b>, fat_type: FatType, cluster: u32)
-    -> iter::Chain<iter::Once<io::Result<u32>>, ClusterIterator<'a, 'b>> {
+    -> ClusterIterator<'a, 'b> {
-        let iter = ClusterIterator {
+        ClusterIterator {
-            rdr: rdr,
+            fat: fat,
             fat_type: fat_type,
             cluster: Some(cluster),
             err: false,
+        }
+    }
+    
+    pub(crate) fn truncate(&mut self) -> io::Result<()> {
+        match self.cluster {
+            Some(n) => {
+                write_fat(&mut self.fat, self.fat_type, n, FatValue::EndOfChain)?;
+                self.next();
+                self.free()
+            },
+            None => Ok(()),
+        }
+    }
+    
+    pub(crate) fn free(&mut self) -> io::Result<()> {
+        loop {
+            let prev = self.cluster;
+            self.next();
+            match prev {
+                Some(n) => write_fat(&mut self.fat, self.fat_type, n, FatValue::Free)?,
+                None => break,
             };
-        iter::once(Ok(cluster)).chain(iter)
+        }
+        Ok(())
     }
 }
 
@@ -79,7 +255,7 @@ impl <'a, 'b> Iterator for ClusterIterator<'a, 'b> {
         }
         match self.cluster {
             Some(current_cluster) => {
-                self.cluster = match get_next_cluster(&mut self.rdr, self.fat_type, current_cluster) {
+                self.cluster = match get_next_cluster(&mut self.fat, self.fat_type, current_cluster) {
                     Ok(next_cluster) => next_cluster,
                     Err(err) => {
                         self.err = true;

tests/write.rs

@@ -15,11 +15,13 @@ const IMG_DIR: &str = "resources";
 const TMP_DIR: &str = "tmp";
 const TEST_STR: &str = "Hi there Rust programmer!\n";
 
-fn call_with_fs(f: &Fn(FileSystem) -> (), filename: &str) {
+fn call_with_fs(f: &Fn(FileSystem) -> (), filename: &str, test_seq: u32) {
     let img_path = format!("{}/{}", IMG_DIR, filename);
-    let tmp_path = format!("{}/{}", TMP_DIR, filename);
+    let tmp_path = format!("{}/{}-{}", TMP_DIR, test_seq, filename);
     fs::create_dir(TMP_DIR).ok();
     fs::copy(&img_path, &tmp_path).unwrap();
+    {
+        // TODO: fix BufStream
         // let file = fs::OpenOptions::new().read(true).write(true).open(&tmp_path).unwrap();
         // let mut buf_file = BufStream::new(file);
         // let fs = FileSystem::new(&mut buf_file).unwrap();
@@ -27,11 +29,13 @@ fn call_with_fs(f: &Fn(FileSystem) -> (), filename: &str) {
         let fs = FileSystem::new(&mut file).unwrap();
         f(fs);
     }
+    fs::remove_file(tmp_path).unwrap();
+}
 
-fn test_write_file(fs: FileSystem) {
+fn test_write_short_file(fs: FileSystem) {
     let mut root_dir = fs.root_dir();
     let mut file = root_dir.open_file("short.txt").expect("open file");
-    file.truncate();
+    file.truncate().unwrap();
     assert_eq!(TEST_STR.len(), file.write(&TEST_STR.as_bytes()).unwrap());
     file.seek(io::SeekFrom::Start(0)).unwrap();
     let mut buf = Vec::new();
@@ -41,15 +45,48 @@ fn test_write_file(fs: FileSystem) {
 
 #[test]
 fn test_write_file_fat12() {
-    call_with_fs(&test_write_file, FAT12_IMG)
+    call_with_fs(&test_write_short_file, FAT12_IMG, 1)
 }
 
 #[test]
 fn test_write_file_fat16() {
-    call_with_fs(&test_write_file, FAT16_IMG)
+    call_with_fs(&test_write_short_file, FAT16_IMG, 1)
 }
 
 #[test]
 fn test_write_file_fat32() {
-    call_with_fs(&test_write_file, FAT32_IMG)
+    call_with_fs(&test_write_short_file, FAT32_IMG, 1)
+}
+
+fn test_write_long_file(fs: FileSystem) {
+    let mut root_dir = fs.root_dir();
+    let mut file = root_dir.open_file("long.txt").expect("open file");
+    file.truncate().unwrap();
+    let test_str = TEST_STR.repeat(100);
+    assert_eq!(test_str.len(), file.write(&test_str.as_bytes()).unwrap());
+    file.seek(io::SeekFrom::Start(0)).unwrap();
+    let mut buf = Vec::new();
+    file.read_to_end(&mut buf).unwrap();
+    assert_eq!(test_str, str::from_utf8(&buf).unwrap());
+    file.seek(io::SeekFrom::Start(1234)).unwrap();
+    file.truncate().unwrap();
+    file.seek(io::SeekFrom::Start(0)).unwrap();
+    buf.clear();
+    file.read_to_end(&mut buf).unwrap();
+    assert_eq!(&test_str[..1234], str::from_utf8(&buf).unwrap());
+}
+
+#[test]
+fn test_write_long_file_fat12() {
+    call_with_fs(&test_write_long_file, FAT12_IMG, 2)
+}
+
+#[test]
+fn test_write_long_file_fat16() {
+    call_with_fs(&test_write_long_file, FAT16_IMG, 2)
+}
+
+#[test]
+fn test_write_long_file_fat32() {
+    call_with_fs(&test_write_long_file, FAT32_IMG, 2)
 }