tape/pool_writer: skip already backed up chunks in iterator

currently, the iterator goes over *all* chunks of the index, even
those already backed up by a previous snapshots in the same tape
backup. this is bad since for each iterator, we stat each chunk to
sort by inode number. so to avoid stat'ing the same chunks over
and over for consecutive snapshots, add a 'skip_fn' to the iterator
and in the pool writer and check the catalog_set if we can skip it

this means we can drop the later check for the catalog_set
(since we don't modify that here)

Signed-off-by: Dominik Csapak <d.csapak@proxmox.com>
Signed-off-by: Dietmar Maurer <dietmar@proxmox.com>

pbs-datastore/src/snapshot_reader.rs

@@ -87,9 +87,9 @@ impl SnapshotReader {
         Ok(file)
     }
 
-    /// Returns an iterator for all used chunks.
-    pub fn chunk_iterator(&self) -> Result<SnapshotChunkIterator, Error> {
-        SnapshotChunkIterator::new(self)
+    /// Returns an iterator for all chunks not skipped by `skip_fn`.
+    pub fn chunk_iterator<F: Fn(&[u8;32]) -> bool>(&self, skip_fn: F) -> Result<SnapshotChunkIterator<F>, Error> {
+        SnapshotChunkIterator::new(self, skip_fn)
     }
 }
 
@@ -98,13 +98,14 @@ impl SnapshotReader {
 /// Note: The iterator returns a `Result`, and the iterator state is
 /// undefined after the first error. So it make no sense to continue
 /// iteration after the first error.
-pub struct SnapshotChunkIterator<'a> {
+pub struct SnapshotChunkIterator<'a, F: Fn(&[u8;32]) -> bool> {
     snapshot_reader: &'a SnapshotReader,
     todo_list: Vec<String>,
+    skip_fn: F,
     current_index: Option<(Arc<Box<dyn IndexFile + Send>>, usize, Vec<(usize, u64)>)>,
 }
 
-impl <'a> Iterator for SnapshotChunkIterator<'a> {
+impl <'a, F: Fn(&[u8;32]) -> bool> Iterator for SnapshotChunkIterator<'a, F> {
     type Item = Result<[u8; 32], Error>;
 
     fn next(&mut self) -> Option<Self::Item> {
@@ -121,7 +122,7 @@ impl <'a> Iterator for SnapshotChunkIterator<'a> {
 
                         let datastore =
                             DataStore::lookup_datastore(self.snapshot_reader.datastore_name())?;
-                        let order = datastore.get_chunks_in_order(&index, |_| false, |_| Ok(()))?;
+                        let order = datastore.get_chunks_in_order(&index, &self.skip_fn, |_| Ok(()))?;
 
                         self.current_index = Some((Arc::new(index), 0, order));
                     } else {
@@ -142,9 +143,9 @@ impl <'a> Iterator for SnapshotChunkIterator<'a> {
     }
 }
 
-impl <'a> SnapshotChunkIterator<'a> {
+impl <'a, F: Fn(&[u8;32]) -> bool> SnapshotChunkIterator<'a, F> {
 
-    pub fn new(snapshot_reader: &'a SnapshotReader) -> Result<Self, Error> {
+    pub fn new(snapshot_reader: &'a SnapshotReader, skip_fn: F) -> Result<Self, Error> {
 
         let mut todo_list = Vec::new();
 
@@ -157,6 +158,6 @@ impl <'a> SnapshotChunkIterator<'a> {
             }
         }
 
-        Ok(Self { snapshot_reader, todo_list, current_index: None })
+        Ok(Self { snapshot_reader, todo_list, current_index: None, skip_fn })
     }
 }