From becceedc4d9bc1435099c90a0514945a89844d3a Mon Sep 17 00:00:00 2001 From: Eric Blake Date: Wed, 17 Feb 2016 23:48:26 -0700 Subject: qapi: Don't box struct branch of alternate There's no reason to do two malloc's for an alternate type visiting a QAPI struct; let's just inline the struct directly as the C union branch of the struct. Surprisingly, no clients were actually using the struct member prior to this patch outside of the testsuite; an earlier patch in the series added some testsuite coverage to make the effect of this patch more obvious. In qapi.py, c_type() gains a new is_unboxed flag to control when we are emitting a C struct unboxed within the context of an outer struct (different from our other two modes of usage with no flags for normal local variable declarations, and with is_param for adding 'const' in a parameter list). I don't know if there is any more pythonic way of collapsing the two flags into a single parameter, as we never have a caller setting both flags at once. Ultimately, we want to also unbox branches for QAPI unions, but as that touches a lot more client code, it is better as separate patches. But since unions and alternates share gen_variants(), I had to hack in a way to test if we are visiting an alternate type for setting the is_unboxed flag: look for a non-object branch. This works because alternates have at least two branches, with at most one object branch, while unions have only object branches. The hack will go away in a later patch. The generated code difference to qapi-types.h is relatively small: | struct BlockdevRef { | QType type; | union { /* union tag is @type */ | void *data; |- BlockdevOptions *definition; |+ BlockdevOptions definition; | char *reference; | } u; | }; The corresponding spot in qapi-visit.c calls visit_type_FOO(), which first calls visit_start_struct() to allocate or deallocate the member and handle a layer of {} from the JSON stream, then visits the members. To peel off the indirection and the memory management that comes with it, we inline this call, then suppress allocation / deallocation by passing NULL to visit_start_struct(), and adjust the member visit: | switch ((*obj)->type) { | case QTYPE_QDICT: |- visit_type_BlockdevOptions(v, name, &(*obj)->u.definition, &err); |+ visit_start_struct(v, name, NULL, 0, &err); |+ if (err) { |+ break; |+ } |+ visit_type_BlockdevOptions_fields(v, &(*obj)->u.definition, &err); |+ error_propagate(errp, err); |+ err = NULL; |+ visit_end_struct(v, &err); | break; | case QTYPE_QSTRING: | visit_type_str(v, name, &(*obj)->u.reference, &err); The visit of non-object fields is unchanged. Signed-off-by: Eric Blake Message-Id: <1455778109-6278-13-git-send-email-eblake@redhat.com> [Commit message tweaked] Signed-off-by: Markus Armbruster --- scripts/qapi-types.py | 10 +++++++++- 1 file changed, 9 insertions(+), 1 deletion(-) (limited to 'scripts/qapi-types.py') diff --git a/scripts/qapi-types.py b/scripts/qapi-types.py index 6ea0ae6fb7..4dabe91c92 100644 --- a/scripts/qapi-types.py +++ b/scripts/qapi-types.py @@ -116,6 +116,14 @@ static inline %(base)s *qapi_%(c_name)s_base(const %(c_name)s *obj) def gen_variants(variants): + # HACK: Determine if this is an alternate (at least one variant + # is not an object); unions have all branches as objects. + unboxed = False + for v in variants.variants: + if not isinstance(v.type, QAPISchemaObjectType): + unboxed = True + break + # 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 @@ -136,7 +144,7 @@ def gen_variants(variants): ret += mcgen(''' %(c_type)s %(c_name)s; ''', - c_type=typ.c_type(), + c_type=typ.c_type(is_unboxed=unboxed), c_name=c_name(var.name)) ret += mcgen(''' -- cgit 1.4.1