qcow2_format.py: collect fields to dump in JSON format

As __dict__ is being extended with class members we do not want to
print, add the to_json() method to classes that returns a json-dumpable
object with desired fields and their values. Extend it in subclass when
necessary to print the final dictionary in the JSON output which
follows.

Suggested-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
Signed-off-by: Andrey Shinkevich <andrey.shinkevich@virtuozzo.com>
Message-Id: <1596742557-320265-10-git-send-email-andrey.shinkevich@virtuozzo.com>
Reviewed-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
Signed-off-by: Eric Blake <eblake@redhat.com>

tests/qemu-iotests/qcow2_format.py

@@ -119,6 +119,9 @@ def dump(self, is_json=False):
 
             print('{:<25} {}'.format(f[2], value_str))
 
+    def to_json(self):
+        return dict((f[2], self.__dict__[f[2]]) for f in self.fields)
+
 
 class Qcow2BitmapExt(Qcow2Struct):
 
@@ -151,6 +154,11 @@ def dump(self):
             print()
             entry.dump()
 
+    def to_json(self):
+        fields_dict = super().to_json()
+        fields_dict['bitmap_directory'] = self.bitmap_directory
+        return fields_dict
+
 
 class Qcow2BitmapDirEntry(Qcow2Struct):
 
@@ -189,6 +197,14 @@ def dump(self):
         super(Qcow2BitmapDirEntry, self).dump()
         self.bitmap_table.dump()
 
+    def to_json(self):
+        # Put the name ahead of the dict
+        return {
+            'name': self.name,
+            **super().to_json(),
+            'bitmap_table': self.bitmap_table
+        }
+
 
 class Qcow2BitmapTableEntry(Qcow2Struct):
 
@@ -214,6 +230,10 @@ def __init__(self, fd):
         else:
             self.type = 'all-zeroes'
 
+    def to_json(self):
+        return {'type': self.type, 'offset': self.offset,
+                'reserved': self.reserved}
+
 
 class Qcow2BitmapTable:
 
@@ -234,6 +254,9 @@ def dump(self):
                 size = 0
             print(f'{i:<14} {entry.type:<15} {size:<12} {entry.offset}')
 
+    def to_json(self):
+        return self.entries
+
 
 QCOW2_EXT_MAGIC_BITMAPS = 0x23852875
 
@@ -249,6 +272,9 @@ class Magic(Enum):
             0x44415441: 'Data file'
         }
 
+        def to_json(self):
+            return self.mapping.get(self.value, "<unknown>")
+
     fields = (
         ('u32', Magic, 'magic'),
         ('u32', '{}', 'length')
@@ -311,6 +337,16 @@ def dump(self):
         else:
             self.obj.dump()
 
+    def to_json(self):
+        # Put the name ahead of the dict
+        res = {'name': self.Magic(self.magic), **super().to_json()}
+        if self.obj is not None:
+            res['data'] = self.obj
+        else:
+            res['data_str'] = self.data_str
+
+        return res
+
     @classmethod
     def create(cls, magic, data):
         return QcowHeaderExtension(magic, len(data), data)