qemu-iotests: add qcow2.py set-feature-bit command

This new command sets feature bits in the image file header:

  qcow2.py set-feature-bit incompatible|compatible|autoclear <bit>

The bit number must be in the range [0, 64).
Signed-off-by: NStefan Hajnoczi <stefanha@linux.vnet.ibm.com>
Signed-off-by: NKevin Wolf <kwolf@redhat.com>

tests/qemu-iotests/qcow2.py

@@ -181,10 +181,33 @@ def cmd_del_header_ext(fd, magic):
 
     h.update(fd)
 
+def cmd_set_feature_bit(fd, group, bit):
+    try:
+        bit = int(bit, 0)
+        if bit < 0 or bit >= 64:
+            raise ValueError
+    except:
+        print "'%s' is not a valid bit number in range [0, 64)" % bit
+        sys.exit(1)
+
+    h = QcowHeader(fd)
+    if group == 'incompatible':
+        h.incompatible_features |= 1 << bit
+    elif group == 'compatible':
+        h.compatible_features |= 1 << bit
+    elif group == 'autoclear':
+        h.autoclear_features |= 1 << bit
+    else:
+        print "'%s' is not a valid group, try 'incompatible', 'compatible', or 'autoclear'" % group
+        sys.exit(1)
+
+    h.update(fd)
+
 cmds = [
     [ 'dump-header',    cmd_dump_header,    0, 'Dump image header and header extensions' ],
     [ 'add-header-ext', cmd_add_header_ext, 2, 'Add a header extension' ],
     [ 'del-header-ext', cmd_del_header_ext, 1, 'Delete a header extension' ],
+    [ 'set-feature-bit', cmd_set_feature_bit, 2, 'Set a feature bit'],
 ]
 
 def main(filename, cmd, args):