tape restore: avoid multiple stat calls for same chunk

src/backup/datastore.rs

@@ -154,10 +154,18 @@ impl DataStore {
     }
 
     /// Fast index verification - only check if chunks exists
-    pub fn fast_index_verification(&self, index: &dyn IndexFile) -> Result<(), Error> {
+    pub fn fast_index_verification(
+        &self,
+        index: &dyn IndexFile,
+        checked: &mut HashSet<[u8;32]>,
+    ) -> Result<(), Error> {
 
         for pos in 0..index.index_count() {
             let info = index.chunk_info(pos).unwrap();
+            if checked.contains(&info.digest) {
+                continue;
+            }
+
             self.stat_chunk(&info.digest).
                 map_err(|err| {
                     format_err!(
@@ -166,6 +174,8 @@ impl DataStore {
                         err,
                     )
                 })?;
+
+            checked.insert(info.digest);
         }
 
         Ok(())