ChunkerFixed sparse handling tests (master)

src/borg/chunkers/reader.pyx

@@ -137,8 +137,11 @@ class FileFMAPReader:
         if self.try_sparse:
             try:
                 fmap = list(sparsemap(self.fd, self.fh))
-            except OSError as err:
-                # seeking did not work
+            except (OSError, ValueError) as err:
+                # Building a sparse map failed:
+                # - OSError: low-level lseek with SEEK_HOLE/SEEK_DATA not supported by FS/OS.
+                # - ValueError: high-level file objects (e.g. io.BytesIO or some fd wrappers)
+                #   don't accept SEEK_HOLE/SEEK_DATA as a valid "whence" and raise ValueError.
                 pass
 
         if fmap is None:
@@ -170,6 +173,9 @@ class FileFMAPReader:
                     # read block from the range
                     data = dread(offset, wanted, self.fd, self.fh)
                     got = len(data)
+                    # Detect zero-filled blocks regardless of sparse mode.
+                    # Zero detection is important to avoid reading/storing allocated zeros
+                    # even when we are not using sparse file handling based on SEEK_HOLE/SEEK_DATA.
                     if zeros.startswith(data):
                         data = None
                         allocation = CH_ALLOC
@@ -321,7 +327,12 @@ class FileReader:
 
         # Determine the allocation type of the resulting chunk
         if has_data:
-            # If any chunk was CH_DATA, the result is CH_DATA
+            # If any chunk was CH_DATA, check if the result is all zeros.
+            # This can happen when a large CH_DATA block (read at read_size granularity)
+            # contains both real data and zero-filled regions, and we are slicing out
+            # a zero-filled portion at the block_size granularity.
+            if zeros.startswith(result):
+                return Chunk(None, size=bytes_read, allocation=CH_ALLOC)
             return Chunk(bytes(result), size=bytes_read, allocation=CH_DATA)
         elif has_hole:
             # If any chunk was CH_HOLE (and none were CH_DATA), the result is CH_HOLE

src/borg/testsuite/chunkers/__init__.py

@@ -77,14 +77,38 @@ def fs_supports_sparse():
 BS = 4096  # filesystem block size
 
 # Some sparse files. X = content blocks, _ = sparse blocks.
+# Block size must always be BS.
+
 # X__XXX____
-map_sparse1 = [(0 * BS, 1 * BS, True), (1 * BS, 2 * BS, False), (3 * BS, 3 * BS, True), (6 * BS, 4 * BS, False)]
+map_sparse1 = [
+    (0, BS, True),
+    (1 * BS, BS, False),
+    (2 * BS, BS, False),
+    (3 * BS, BS, True),
+    (4 * BS, BS, True),
+    (5 * BS, BS, True),
+    (6 * BS, BS, False),
+    (7 * BS, BS, False),
+    (8 * BS, BS, False),
+    (9 * BS, BS, False),
+]
 
 # _XX___XXXX
-map_sparse2 = [(0 * BS, 1 * BS, False), (1 * BS, 2 * BS, True), (3 * BS, 3 * BS, False), (6 * BS, 4 * BS, True)]
+map_sparse2 = [
+    (0, BS, False),
+    (1 * BS, BS, True),
+    (2 * BS, BS, True),
+    (3 * BS, BS, False),
+    (4 * BS, BS, False),
+    (5 * BS, BS, False),
+    (6 * BS, BS, True),
+    (7 * BS, BS, True),
+    (8 * BS, BS, True),
+    (9 * BS, BS, True),
+]
 
 # XXX
-map_notsparse = [(0 * BS, 3 * BS, True)]
+map_notsparse = [(0, BS, True), (BS, BS, True), (2 * BS, BS, True)]
 
 # ___
-map_onlysparse = [(0 * BS, 3 * BS, False)]
+map_onlysparse = [(0, BS, False), (BS, BS, False), (2 * BS, BS, False)]

src/borg/testsuite/chunkers/fixed_test.py

@@ -4,13 +4,42 @@
 
 import pytest
 
-from . import cf, cf_expand, make_sparsefile, make_content, fs_supports_sparse
+from . import cf, cf_expand, make_sparsefile, make_content
 from . import BS, map_sparse1, map_sparse2, map_onlysparse, map_notsparse
 from ...chunkers import ChunkerFixed
 from ...constants import *  # NOQA
 
 
-@pytest.mark.skipif(not fs_supports_sparse(), reason="filesystem does not support sparse files")
+def pretty_print(msg, items):
+    """
+    Pretty-print the result of get_chunks.
+
+    For each element in the sequence:
+    - If it's a bytes object consisting solely of b"H", print "header length: X" where X is its length.
+    - If it's a bytes object consisting solely of b"X", print "body length: X" where X is its length.
+    - If it's an int, print "sparse: length: X" where X is the integer value (interpreted as a length).
+    """
+    print(msg)
+    print("-" * len(msg))
+    for item in items:
+        if isinstance(item, bytes):
+            # Detect sequences of only 'H' (header) or only 'X' (body)
+            if item.replace(b"H", b"") == b"":
+                print(f"header({len(item)})")
+            elif item.replace(b"X", b"") == b"":
+                print(f"body({len(item)})")
+            elif item.replace(b"\0", b"") == b"":
+                print(f"zeros({len(item)})")
+            else:
+                # Fallback: unknown content, print as body with its length
+                print(f"other({len(item)})")
+        elif isinstance(item, int):
+            print(f"sparse({item})")
+        else:
+            # Unexpected element type, just print a generic line.
+            print(f"???({item})")
+
+
 @pytest.mark.parametrize(
     "fname, sparse_map, header_size, sparse",
     [
@@ -34,13 +63,19 @@
 )
 def test_chunkify_sparse(tmpdir, fname, sparse_map, header_size, sparse):
     def get_chunks(fname, sparse, header_size):
-        chunker = ChunkerFixed(4096, header_size=header_size, sparse=sparse)
+        chunker = ChunkerFixed(BS, header_size=header_size, sparse=sparse)
         with open(fname, "rb") as fd:
             return cf(chunker.chunkify(fd))
 
+    # this only works if sparse map blocks are same size as fixed chunker blocks
     fn = str(tmpdir / fname)
     make_sparsefile(fn, sparse_map, header_size=header_size)
-    get_chunks(fn, sparse=sparse, header_size=header_size) == make_content(sparse_map, header_size=header_size)
+    expected_content = make_content(sparse_map, header_size=header_size)
+    got_chunks = get_chunks(fn, sparse=sparse, header_size=header_size)
+    print(f"sparse: {sparse}")
+    pretty_print("expected", expected_content)
+    pretty_print("got", got_chunks)
+    assert expected_content == got_chunks
 
 
 @pytest.mark.skipif("BORG_TESTS_SLOW" not in os.environ, reason="slow tests not enabled, use BORG_TESTS_SLOW=1")

src/borg/testsuite/chunkers/reader_test.py

@@ -9,6 +9,22 @@
 from ...constants import *  # NOQA
 
 
+def coalesce_sparse_map(sparse_map):
+    """Coalesce adjacent ranges with the same is_data flag, as the OS would report them."""
+    if not sparse_map:
+        return []
+    result = []
+    start, size, is_data = sparse_map[0]
+    for next_start, next_size, next_is_data in sparse_map[1:]:
+        if next_is_data == is_data:
+            size += next_size
+        else:
+            result.append((start, size, is_data))
+            start, size, is_data = next_start, next_size, next_is_data
+    result.append((start, size, is_data))
+    return result
+
+
 @pytest.mark.skipif(not fs_supports_sparse(), reason="filesystem does not support sparse files")
 @pytest.mark.parametrize(
     "fname, sparse_map",
@@ -28,8 +44,11 @@ def get_sparsemap_fd(fname):
 
     fn = str(tmpdir / fname)
     make_sparsefile(fn, sparse_map)
-    assert get_sparsemap_fh(fn) == sparse_map
-    assert get_sparsemap_fd(fn) == sparse_map
+    # The OS coalesces adjacent ranges of the same type (data or hole),
+    # so we compare against the coalesced version of the expected map.
+    expected = coalesce_sparse_map(sparse_map)
+    assert get_sparsemap_fh(fn) == expected
+    assert get_sparsemap_fd(fn) == expected
 
 
 @pytest.mark.parametrize(