Fix qcow2 support for absolute and relative backing_file paths (#65)

Signed-off-by: Andreia Ocanoaia <andreia.ocanoaia@gmail.com>
Co-authored-by: Schamper <1254028+Schamper@users.noreply.github.com>

Author: andreia-oca

dissect/hypervisor/disk/qcow2.py

@@ -176,7 +176,7 @@ def _open_data_file(self, data_file: BinaryIO | None, allow_no_data_file: bool =
             return data_file
 
         if self.path:
-            if (data_file_path := self.path.with_name(self.image_data_file)).exists():
+            if (data_file_path := self.path.parent.joinpath(self.image_data_file)).exists():
                 return data_file_path.open("rb")
 
             if not allow_no_data_file:
@@ -190,7 +190,7 @@ def _open_backing_file(self, backing_file: BinaryIO | None, allow_no_backing_fil
         backing_file_path = None
         if backing_file is None:
             if self.path:
-                if (backing_file_path := self.path.with_name(self.auto_backing_file)).exists():
+                if (backing_file_path := self.path.parent.joinpath(self.auto_backing_file)).exists():
                     backing_file = backing_file_path.open("rb")
                 elif not allow_no_backing_file:
                     raise Error(

tests/disk/test_qcow2.py

@@ -72,6 +72,15 @@ def test_data_file() -> None:
             for i in range(255):
                 assert stream.read(1024 * 1024).strip(bytes([i])) == b"", f"Mismatch at offset {i * 1024 * 1024:#x}"
 
+    # Test with absolute path
+    with patch.object(Path, "open", lambda *args: None), patch.object(Path, "exists", return_value=False):
+        qcow2.image_data_file = "/absolute/path/to/nothing.qcow2"
+        with pytest.raises(
+            Error,
+            match=r"data-file '(?:[A-Z]:\\+)?[/\\]+absolute[/\\]+path[/\\]+to[/\\]+nothing\.qcow2' not found \(image_data_file = '/absolute/path/to/nothing\.qcow2'\)",  # noqa: E501
+        ):
+            qcow2._open_data_file(None)
+
 
 def test_backing_file() -> None:
     file1 = absolute_path("_data/disk/qcow2/backing-chain-1.qcow2.gz")
@@ -136,6 +145,15 @@ def test_backing_file() -> None:
             assert stream.read(1024 * 1024).strip(b"\x00") == b"Something here four"
             assert stream.read(1024 * 1024).strip(b"\x00") == b"Something here five"
 
+    # Test with absolute path
+    with patch.object(Path, "open", lambda *args: None), patch.object(Path, "exists", return_value=False):
+        qcow2.auto_backing_file = "/absolute/path/to/nothing.qcow2"
+        with pytest.raises(
+            Error,
+            match=r"backing-file '(?:[A-Z]:\\+)?[/\\]+absolute[/\\]+path[/\\]+to[/\\]+nothing\.qcow2' not found \(auto_backing_file = '/absolute/path/to/nothing\.qcow2'\)",  # noqa: E501
+        ):
+            qcow2._open_backing_file(None)
+
 
 def test_snapshot() -> None:
     with gzip.open(absolute_path("_data/disk/qcow2/snapshot.qcow2.gz"), "rb") as fh: