mount: fuse fs performance fix, docstring

src/borg/fuse.py

@@ -1,3 +1,18 @@
+"""
+FUSE filesystem implementation for `borg mount`.
+
+IMPORTANT
+=========
+
+This code is only safe for single-threaded and synchronous (non-async) usage.
+
+- llfuse is synchronous and used with workers=1, so there is only 1 thread,
+  and we are safe.
+- pyfuse3 uses Trio, which only uses 1 thread, but could use this code in an
+  asynchronous manner. However, as long as we do not use any asynchronous
+  operations (like using "await") in this code, it is still de facto
+  synchronous, and we are safe.
+"""
 import errno
 import functools
 import io
@@ -162,7 +177,7 @@ def iter_archive_items(self, archive_item_ids, filter=None, consider_part_files=
         for key, (csize, data) in zip(archive_item_ids, self.decrypted_repository.get_many(archive_item_ids)):
             # Store the chunk ID in the meta-array
             if write_offset + 32 >= len(meta):
-                self.meta = meta = meta + bytes(self.GROW_META_BY)
+                meta.extend(bytes(self.GROW_META_BY))
             meta[write_offset:write_offset + 32] = key
             current_id_offset = write_offset
             write_offset += 32
@@ -200,7 +215,7 @@ def iter_archive_items(self, archive_item_ids, filter=None, consider_part_files=
                 msgpacked_bytes = b''
 
                 if write_offset + 9 >= len(meta):
-                    self.meta = meta = meta + bytes(self.GROW_META_BY)
+                    meta.extend(bytes(self.GROW_META_BY))
 
                 # item entries in the meta-array come in two different flavours, both nine bytes long.
                 # (1) for items that span chunks: