block/vmdk: Change extent info type

VMDK's implementation of .bdrv_get_specific_info() returns information
about its extent files, ostensibly in the form of ImageInfo objects.
However, it does not get this information through
bdrv_query_image_info(), but fills only a select few fields with custom
information that does not always match the fields' purposes.

For example, @format, which is supposed to be a block driver name, is
filled with the extent type, e.g. SPARSE or FLAT.

In ImageInfo, @compressed shows whether the data that can be seen in the
image is stored in compressed form or not.  For example, a compressed
qcow2 image will store compressed data in its data file, but when
accessing the qcow2 node, you will see normal data.  This is not how
VMDK uses the @compressed field for its extent files: Instead, it
signifies whether accessing the extent file will yield compressed data
(which the VMDK driver then (de-)compresses).

Create a new structure to represent the extent information.  This allows
us to clarify the fields' meanings, and it clearly shows that these are
not complete ImageInfo objects.  (That is, if a user wants an extent
file's ImageInfo object, they will need to query it separately, and will
not get it from ImageInfoSpecificVmdk.extents.)

Note that this removes the last use of ['ImageInfo'] (i.e. an array of
ImageInfo objects), so the QAPI generator will no longer generate
ImageInfoList by default.  However, we use it in qemu-img.c, so we need
to create a dummy object to force the generate to create that type,
similarly to DummyForceArrays in machine.json (introduced in commit
9f08c8ec73 ("qapi: Lazy creation of array
types")).

Signed-off-by: Hanna Reitz <hreitz@redhat.com>
Message-Id: <20220620162704.80987-4-hreitz@redhat.com>
Reviewed-by: Kevin Wolf <kwolf@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>

qapi/block-core.json

@@ -124,7 +124,33 @@
       'create-type': 'str',
       'cid': 'int',
       'parent-cid': 'int',
-      'extents': ['ImageInfo']
+      'extents': ['VmdkExtentInfo']
+  } }
+
+##
+# @VmdkExtentInfo:
+#
+# Information about a VMDK extent file
+#
+# @filename: Name of the extent file
+#
+# @format: Extent type (e.g. FLAT or SPARSE)
+#
+# @virtual-size: Number of bytes covered by this extent
+#
+# @cluster-size: Cluster size in bytes (for non-flat extents)
+#
+# @compressed: Whether this extent contains compressed data
+#
+# Since: 8.0
+##
+{ 'struct': 'VmdkExtentInfo',
+  'data': {
+      'filename': 'str',
+      'format': 'str',
+      'virtual-size': 'int',
+      '*cluster-size': 'int',
+      '*compressed': 'bool'
   } }
 
 ##
@@ -5754,3 +5780,13 @@
   'data': { 'device': 'str', '*id': 'str', '*name': 'str'},
   'returns': 'SnapshotInfo',
   'allow-preconfig': true }
+
+##
+# @DummyBlockCoreForceArrays:
+#
+# Not used by QMP; hack to let us use ImageInfoList internally
+#
+# Since: 8.0
+##
+{ 'struct': 'DummyBlockCoreForceArrays',
+  'data': { 'unused-image-info': ['ImageInfo'] } }