diff --git a/src/block_manager.rs b/src/block_manager.rs
index 5abef18..7aebbaf 100644
--- a/src/block_manager.rs
+++ b/src/block_manager.rs
@@ -141,7 +141,8 @@ impl Clone for AsyncIoEngine {
     fn clone(&self) -> AsyncIoEngine {
         let inner = self.inner.lock().unwrap();
         eprintln!("in clone, queue_len = {}", inner.queue_len);
-        AsyncIoEngine {inner: Mutex::new(AsyncIoEngine_ {
+        AsyncIoEngine {
+            inner: Mutex::new(AsyncIoEngine_ {
                 queue_len: inner.queue_len,
                 ring: IoUring::new(inner.queue_len).expect("couldn't create uring"),
                 nr_blocks: inner.nr_blocks,
diff --git a/src/pdata/btree.rs b/src/pdata/btree.rs
index 3b07c63..00c8620 100644
--- a/src/pdata/btree.rs
+++ b/src/pdata/btree.rs
@@ -10,7 +10,7 @@ use crate::checksum;
 
 //------------------------------------------
 
-pub trait ValueType {
+pub trait Unpack {
     // The size of the value when on disk.
     fn disk_size() -> u32;
     fn unpack(data: &[u8]) -> IResult<&[u8], Self>
@@ -53,7 +53,7 @@ pub fn unpack_node_header(data: &[u8]) -> IResult<&[u8], NodeHeader> {
     ))
 }
 
-pub enum Node<V: ValueType> {
+pub enum Node<V: Unpack> {
     Internal {
         header: NodeHeader,
         keys: Vec<u64>,
@@ -79,7 +79,7 @@ pub fn to_any<'a, V>(r: IResult<&'a [u8], V>) -> Result<(&'a [u8], V)> {
     }
 }
 
-pub fn unpack_node<V: ValueType>(
+pub fn unpack_node<V: Unpack>(
     data: &[u8],
     ignore_non_fatal: bool,
     is_root: bool,
@@ -154,7 +154,7 @@ pub fn unpack_node<V: ValueType>(
 
 //------------------------------------------
 
-impl ValueType for u64 {
+impl Unpack for u64 {
     fn disk_size() -> u32 {
         8
     }
@@ -166,7 +166,7 @@ impl ValueType for u64 {
 
 //------------------------------------------
 
-pub trait NodeVisitor<V: ValueType> {
+pub trait NodeVisitor<V: Unpack> {
     fn visit<'a>(&mut self, w: &BTreeWalker, b: &Block, node: &Node<V>) -> Result<()>;
 }
 
@@ -208,7 +208,7 @@ impl BTreeWalker {
     fn walk_nodes<NV, V>(&mut self, visitor: &mut NV, bs: &Vec<u64>) -> Result<()>
     where
         NV: NodeVisitor<V>,
-        V: ValueType,
+        V: Unpack,
     {
         let mut blocks = Vec::new();
         let seen = self.seen.lock().unwrap();
@@ -231,7 +231,7 @@ impl BTreeWalker {
     fn walk_node<NV, V>(&mut self, visitor: &mut NV, b: &Block, is_root: bool) -> Result<()>
     where
         NV: NodeVisitor<V>,
-        V: ValueType,
+        V: Unpack,
     {
         let mut seen = self.seen.lock().unwrap();
         seen.insert(b.loc as usize);
@@ -260,7 +260,7 @@ impl BTreeWalker {
     pub fn walk_b<NV, V>(&mut self, visitor: &mut NV, root: &Block) -> Result<()>
     where
         NV: NodeVisitor<V>,
-        V: ValueType,
+        V: Unpack,
     {
         self.walk_node(visitor, &root, true)
     }
@@ -268,7 +268,7 @@ impl BTreeWalker {
     pub fn walk<NV, V>(&mut self, visitor: &mut NV, root: u64) -> Result<()>
     where
         NV: NodeVisitor<V>,
-        V: ValueType,
+        V: Unpack,
     {
         let mut root = Block::new(root);
         self.engine.read(&mut root)?;
diff --git a/src/thin/check.rs b/src/thin/check.rs
index 207b69f..3611248 100644
--- a/src/thin/check.rs
+++ b/src/thin/check.rs
@@ -8,7 +8,7 @@ use std::time::Instant;
 use threadpool::ThreadPool;
 
 use crate::block_manager::{AsyncIoEngine, Block, IoEngine};
-use crate::pdata::btree::{BTreeWalker, Node, NodeVisitor, ValueType};
+use crate::pdata::btree::{BTreeWalker, Node, NodeVisitor, Unpack};
 use crate::thin::superblock::*;
 
 //------------------------------------------
@@ -18,7 +18,7 @@ struct TopLevelVisitor<'a> {
 }
 
 impl<'a> NodeVisitor<u64> for TopLevelVisitor<'a> {
-    fn visit(&mut self, w: &BTreeWalker, _b: &Block, node: &Node<u64>) -> Result<()> {
+    fn visit(&mut self, _w: &BTreeWalker, _b: &Block, node: &Node<u64>) -> Result<()> {
         if let Node::Leaf {
             header: _h,
             keys,
@@ -44,7 +44,7 @@ struct BlockTime {
     time: u32,
 }
 
-impl ValueType for BlockTime {
+impl Unpack for BlockTime {
     fn disk_size() -> u32 {
         8
     }
@@ -82,7 +82,7 @@ struct DeviceDetail {
     snapshotted_time: u32,
 }
 
-impl ValueType for DeviceDetail {
+impl Unpack for DeviceDetail {
     fn disk_size() -> u32 {
         24
     }
@@ -139,8 +139,7 @@ impl NodeVisitor<DeviceDetail> for DeviceVisitor {
 //------------------------------------------
 
 pub fn check(dev: &Path) -> Result<()> {
-    //let mut engine = SyncIoEngine::new(dev)?;
-    let mut engine = Arc::new(AsyncIoEngine::new(dev, 256)?);
+    let engine = Arc::new(AsyncIoEngine::new(dev, 256)?);
 
     let now = Instant::now();
     let sb = read_superblock(engine.as_ref(), SUPERBLOCK_LOCATION)?;
@@ -165,7 +164,7 @@ pub fn check(dev: &Path) -> Result<()> {
     {
         let nr_workers = 4;
         let pool = ThreadPool::new(nr_workers);
-        let mut seen = Arc::new(Mutex::new(FixedBitSet::with_capacity(
+        let seen = Arc::new(Mutex::new(FixedBitSet::with_capacity(
             engine.get_nr_blocks() as usize,
         )));