[PULL 08/15] qcow2_format.py: use strings to specify c-type of struct fields

[Eric Blake]

From: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>

We are going to move field-parsing to super-class, this will be simpler
with simple string specifiers instead of variables.

For some reason, python doesn't allow the definition of ctypes variable
in the class alongside fields: it would not be available then for use
by the 'for' operator. Don't worry: ctypes will be moved to metaclass
soon.

Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
Reviewed-by: Andrey Shinkevich <andrey.shinkevich@virtuozzo.com>
Message-Id: <20200606081806.23897-8-vsementsov@virtuozzo.com>
Signed-off-by: Eric Blake <eblake@redhat.com>
---
 tests/qemu-iotests/qcow2_format.py | 50 +++++++++++++++++-------------
 1 file changed, 28 insertions(+), 22 deletions(-)

diff --git a/tests/qemu-iotests/qcow2_format.py 
b/tests/qemu-iotests/qcow2_format.py
index da66df340876..28f2bfa63bc7 100644
--- a/tests/qemu-iotests/qcow2_format.py
+++ b/tests/qemu-iotests/qcow2_format.py
@@ -34,36 +34,42 @@ class QcowHeaderExtension:
         return QcowHeaderExtension(magic, len(data), data)


+# Mapping from c types to python struct format
+ctypes = {
+    'u8': 'B',
+    'u16': 'H',
+    'u32': 'I',
+    'u64': 'Q'
+}
+
+
 class QcowHeader:

-    uint32_t = 'I'
-    uint64_t = 'Q'
-
     fields = (
         # Version 2 header fields
-        (uint32_t, '{:#x}', 'magic'),
-        (uint32_t, '{}', 'version'),
-        (uint64_t, '{:#x}', 'backing_file_offset'),
-        (uint32_t, '{:#x}', 'backing_file_size'),
-        (uint32_t, '{}', 'cluster_bits'),
-        (uint64_t, '{}', 'size'),
-        (uint32_t, '{}', 'crypt_method'),
-        (uint32_t, '{}', 'l1_size'),
-        (uint64_t, '{:#x}', 'l1_table_offset'),
-        (uint64_t, '{:#x}', 'refcount_table_offset'),
-        (uint32_t, '{}', 'refcount_table_clusters'),
-        (uint32_t, '{}', 'nb_snapshots'),
-        (uint64_t, '{:#x}', 'snapshot_offset'),
+        ('u32', '{:#x}', 'magic'),
+        ('u32', '{}', 'version'),
+        ('u64', '{:#x}', 'backing_file_offset'),
+        ('u32', '{:#x}', 'backing_file_size'),
+        ('u32', '{}', 'cluster_bits'),
+        ('u64', '{}', 'size'),
+        ('u32', '{}', 'crypt_method'),
+        ('u32', '{}', 'l1_size'),
+        ('u64', '{:#x}', 'l1_table_offset'),
+        ('u64', '{:#x}', 'refcount_table_offset'),
+        ('u32', '{}', 'refcount_table_clusters'),
+        ('u32', '{}', 'nb_snapshots'),
+        ('u64', '{:#x}', 'snapshot_offset'),

         # Version 3 header fields
-        (uint64_t, 'mask', 'incompatible_features'),
-        (uint64_t, 'mask', 'compatible_features'),
-        (uint64_t, 'mask', 'autoclear_features'),
-        (uint32_t, '{}', 'refcount_order'),
-        (uint32_t, '{}', 'header_length'),
+        ('u64', 'mask', 'incompatible_features'),
+        ('u64', 'mask', 'compatible_features'),
+        ('u64', 'mask', 'autoclear_features'),
+        ('u32', '{}', 'refcount_order'),
+        ('u32', '{}', 'header_length'),
     )

-    fmt = '>' + ''.join(field[0] for field in fields)
+    fmt = '>' + ''.join(ctypes[f[0]] for f in fields)

     def __init__(self, fd):

-- 
2.27.0