Commit ca56a822 authored by Eric Blake's avatar Eric Blake Committed by Markus Armbruster
Browse files

qapi: Document shortcoming with union 'data' branch 



Add a FIXME to remind us to fully audit whether removing the
'void *data' branch of each qapi union type can be done safely.

Signed-off-by: default avatarEric Blake <eblake@redhat.com>
Message-Id: <1438297637-26789-1-git-send-email-eblake@redhat.com>
Signed-off-by: default avatarMarkus Armbruster <armbru@redhat.com>
parent 2f52e205

scripts/qapi-types.py

+8 −0
Original line number Diff line number Diff line
@@ -219,6 +219,14 @@ struct %(name)s 
''',

                     discriminator_type_name=c_name(discriminator_type_name))



    # FIXME: What purpose does data serve, besides preventing a union that

    # has a branch named 'data'? We use it in qapi-visit.py to decide

    # whether to bypass the switch statement if visiting the discriminator

    # failed; but since we 0-initialize structs, and cannot tell what

    # branch of the union is in use if the discriminator is invalid, there

    # should not be any data leaks even without a data pointer.  Or, if

    # 'data' is merely added to guarantee we don't have an empty union,

    # shouldn't we enforce that at .json parse time?

    ret += mcgen('''

    union { /* union tag is @%(c_name)s */

        void *data;