qcow2_format.py: dump bitmaps header extension

Add class for bitmap extension and dump its fields. Further work is to
dump bitmap directory.

Test new functionality inside 291 iotest.

Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
Reviewed-by: Andrey Shinkevich <andrey.shinkevich@virtuozzo.com>
Message-Id: <20200606081806.23897-14-vsementsov@virtuozzo.com>
[eblake: fix iotest output]
Signed-off-by: Eric Blake <eblake@redhat.com>

tests/qemu-iotests/291

@@ -62,6 +62,8 @@ $QEMU_IO -c 'w 1M 1M' -f $IMGFMT "$TEST_IMG" | _filter_qemu_io
 $QEMU_IMG bitmap --disable -f $IMGFMT "$TEST_IMG" b1
 $QEMU_IMG bitmap --enable -f $IMGFMT "$TEST_IMG" b2
 $QEMU_IO -c 'w 2M 1M' -f $IMGFMT "$TEST_IMG" | _filter_qemu_io
+echo "Check resulting qcow2 header extensions:"
+$PYTHON qcow2.py "$TEST_IMG" dump-header-exts
 
 echo
 echo "=== Bitmap preservation not possible to non-qcow2 ==="
@@ -88,6 +90,8 @@ $QEMU_IMG bitmap --merge tmp -f $IMGFMT "$TEST_IMG" b0
 $QEMU_IMG bitmap --remove --image-opts \
     driver=$IMGFMT,file.driver=file,file.filename="$TEST_IMG" tmp
 $QEMU_IMG info "$TEST_IMG" | _filter_img_info --format-specific
+echo "Check resulting qcow2 header extensions:"
+$PYTHON qcow2.py "$TEST_IMG" dump-header-exts
 
 echo
 echo "=== Check bitmap contents ==="

tests/qemu-iotests/291.out

@@ -14,6 +14,25 @@ wrote 1048576/1048576 bytes at offset 1048576
 1 MiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
 wrote 1048576/1048576 bytes at offset 2097152
 1 MiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
+Check resulting qcow2 header extensions:
+Header extension:
+magic                     0xe2792aca (Backing format)
+length                    5
+data                      'qcow2'
+
+Header extension:
+magic                     0x6803f857 (Feature table)
+length                    336
+data                      <binary>
+
+Header extension:
+magic                     0x23852875 (Bitmaps)
+length                    24
+nb_bitmaps                2
+reserved32                0
+bitmap_directory_size     0x40
+bitmap_directory_offset   0x510000
+
 
 === Bitmap preservation not possible to non-qcow2 ===
 
@@ -65,6 +84,20 @@ Format specific information:
             granularity: 65536
     refcount bits: 16
     corrupt: false
+Check resulting qcow2 header extensions:
+Header extension:
+magic                     0x6803f857 (Feature table)
+length                    336
+data                      <binary>
+
+Header extension:
+magic                     0x23852875 (Bitmaps)
+length                    24
+nb_bitmaps                3
+reserved32                0
+bitmap_directory_size     0x60
+bitmap_directory_offset   0x520000
+
 
 === Check bitmap contents ===
 

tests/qemu-iotests/qcow2_format.py

@@ -103,6 +103,19 @@ class Qcow2Struct(metaclass=Qcow2StructMeta):
             print('{:<25} {}'.format(f[2], value_str))
 
 
+class Qcow2BitmapExt(Qcow2Struct):
+
+    fields = (
+        ('u32', '{}', 'nb_bitmaps'),
+        ('u32', '{}', 'reserved32'),
+        ('u64', '{:#x}', 'bitmap_directory_size'),
+        ('u64', '{:#x}', 'bitmap_directory_offset')
+    )
+
+
+QCOW2_EXT_MAGIC_BITMAPS = 0x23852875
+
+
 class QcowHeaderExtension(Qcow2Struct):
 
     class Magic(Enum):
@@ -110,7 +123,7 @@ class QcowHeaderExtension(Qcow2Struct):
             0xe2792aca: 'Backing format',
             0x6803f857: 'Feature table',
             0x0537be77: 'Crypto header',
-            0x23852875: 'Bitmaps',
+            QCOW2_EXT_MAGIC_BITMAPS: 'Bitmaps',
             0x44415441: 'Data file'
         }
 
@@ -130,8 +143,11 @@ class QcowHeaderExtension(Qcow2Struct):
         This should be somehow refactored and functionality should be moved to
         superclass (to allow creation of any qcow2 struct), but then, fields
         of variable length (data here) should be supported in base class
-        somehow. So, it's a TODO. We'll see how to properly refactor this when
-        we have more qcow2 structures.
+        somehow. Note also, that we probably want to parse different
+        extensions. Should they be subclasses of this class, or how to do it
+        better? Should it be something like QAPI union with discriminator field
+        (magic here). So, it's a TODO. We'll see how to properly refactor this
+        when we have more qcow2 structures.
         """
         if fd is None:
             assert all(v is not None for v in (magic, length, data))
@@ -148,15 +164,23 @@ class QcowHeaderExtension(Qcow2Struct):
             self.data = fd.read(padded)
             assert self.data is not None
 
+        if self.magic == QCOW2_EXT_MAGIC_BITMAPS:
+            self.obj = Qcow2BitmapExt(data=self.data)
+        else:
+            self.obj = None
+
     def dump(self):
+        super().dump()
+
+        if self.obj is None:
             data = self.data[:self.length]
             if all(c in string.printable.encode('ascii') for c in data):
                 data = f"'{ data.decode('ascii') }'"
             else:
                 data = '<binary>'
-
-        super().dump()
             print(f'{"data":<25} {data}')
+        else:
+            self.obj.dump()
 
     @classmethod
     def create(cls, magic, data):