[space_map (rust)] Fix uninitialized bytes in index block

src/pdata/space_map_checker.rs

@@ -190,14 +190,6 @@ fn gather_metadata_index_entries(
 ) -> Result<Vec<IndexEntry>> {
     let b = engine.read(bitmap_root)?;
     let entries = unpack::<MetadataIndex>(b.get_data())?.indexes;
-
-    // Filter out unused entries with block 0
-    let entries: Vec<IndexEntry> = entries
-        .iter()
-        .take_while(|e| e.blocknr != 0)
-        .cloned()
-        .collect();
-
     metadata_sm.lock().unwrap().inc(bitmap_root, 1)?;
     inc_entries(&metadata_sm, &entries[0..])?;
 

src/pdata/space_map_metadata.rs

@@ -34,6 +34,13 @@ impl Unpack for MetadataIndex {
         let (i, blocknr) = le_u64(i)?;
         let (i, indexes) = nom::multi::count(IndexEntry::unpack, MAX_METADATA_BITMAPS)(i)?;
 
+        // Filter out unused entries
+        let indexes: Vec<IndexEntry> = indexes
+            .iter()
+            .take_while(|e| e.blocknr != 0)
+            .cloned()
+            .collect();
+
         Ok((i, MetadataIndex { blocknr, indexes }))
     }
 }
@@ -100,7 +107,7 @@ pub fn write_metadata_sm(w: &mut WriteBatcher, sm: &dyn SpaceMap) -> Result<SMRo
     w.clear_allocations();
     let (mut indexes, ref_count_root) = write_common(w, sm)?;
 
-    let bitmap_root = w.alloc()?;
+    let bitmap_root = w.alloc_zeroed()?;
 
     // Now we need to patch up the counts for the metadata that was used for storing
     // the space map itself.  These ref counts all went from 0 to 1.

src/write_batcher.rs

@@ -47,6 +47,18 @@ impl WriteBatcher {
         Ok(Block::new(b.unwrap()))
     }
 
+    pub fn alloc_zeroed(&mut self) -> Result<Block> {
+        let mut sm = self.sm.lock().unwrap();
+        let b = sm.alloc()?;
+
+        if b.is_none() {
+            return Err(anyhow!("out of metadata space"));
+        }
+
+        self.allocations.insert(b.unwrap());
+        Ok(Block::zeroed(b.unwrap()))
+    }
+
     pub fn clear_allocations(&mut self) -> BTreeSet<u64> {
         let mut tmp = BTreeSet::new();
         std::mem::swap(&mut tmp, &mut self.allocations);