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Improve dm-thin behavior of empty blocks (#32)
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@Schamper
Schamper authored Jul 3, 2024
1 parent 70006bc commit de2aefd
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48 changes: 3 additions & 45 deletions .gitattributes
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tests/data/dm/dm-thin-data.bin.gz filter=lfs diff=lfs merge=lfs -text
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4 changes: 4 additions & 0 deletions dissect/volume/dm/thin.py
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Expand Up @@ -77,6 +77,10 @@ def _read(self, offset: int, length: int) -> bytes:
while length > 0:
block_info = data_mapping.lookup([self.device_id, block])
if block_info is None:
remaining = length
if self.size is None or (remaining := self.size - offset) > 0:
return b"\x00" * min(length, remaining)

break

block_time = int.from_bytes(block_info, "little")
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5 changes: 5 additions & 0 deletions tests/conftest.py
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Expand Up @@ -90,6 +90,11 @@ def dm_thin() -> Iterator[list[BinaryIO]]:
yield from open_files_gz(["data/dm/dm-thin-metadata.bin.gz", "data/dm/dm-thin-data.bin.gz"])


@pytest.fixture
def dm_thin_empty() -> Iterator[list[BinaryIO]]:
yield from open_files_gz(["data/dm/dm-thin-empty-metadata.bin.gz", "data/dm/dm-thin-empty-data.bin.gz"])


@pytest.fixture
def md_linear() -> Iterator[list[BinaryIO]]:
yield from open_files_gz(["data/md/md-linear-1.bin.gz", "data/md/md-linear-2.bin.gz"])
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3 changes: 3 additions & 0 deletions tests/data/dm/dm-thin-empty-data.bin.gz
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3 changes: 3 additions & 0 deletions tests/data/dm/dm-thin-empty-metadata.bin.gz
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22 changes: 21 additions & 1 deletion tests/test_dm.py
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Expand Up @@ -22,4 +22,24 @@ def test_dm_thin(dm_thin: list[BinaryIO]) -> None:

thin_no_size = pool.open(0)
thin_no_size.seek((1024 * 1024 * 2) - 512)
assert len(thin_no_size.read(1024)) == 512
assert len(thin_no_size.read(1024)) == 1024


def test_dm_thin_empty(dm_thin_empty: list[BinaryIO]) -> None:
metadata_fh, data_fh = dm_thin_empty
pool = ThinPool(metadata_fh, data_fh)

dev = pool.open(0)

assert dev.read(512) == b"\x00" * 512

dev.seek(512 * 1024)
assert dev.read(512) != b"\x00" * 512

# Far beyond the file boundary
dev.seek(2**64)
assert dev.read(512) == b"\x00" * 512

dev = pool.open(0, 512)
assert dev.read(512) == b"\x00" * 512
assert dev.read(512) == b""

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