From 12dabf0640949138700931e877669c4cf677d488 Mon Sep 17 00:00:00 2001 From: Eric Blake Date: Tue, 20 Feb 2018 16:30:59 -0500 Subject: [PATCH] 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. Backports commit becceedc4d9bc1435099c90a0514945a89844d3a from qemu --- qemu/scripts/qapi-types.py | 10 +++++++++- qemu/scripts/qapi-visit.py | 35 ++++++++++++++++++++++++++++------- qemu/scripts/qapi.py | 12 +++++++----- 3 files changed, 44 insertions(+), 13 deletions(-) diff --git a/qemu/scripts/qapi-types.py b/qemu/scripts/qapi-types.py index ebc0f662..c26eeb5b 100644 --- a/qemu/scripts/qapi-types.py +++ b/qemu/scripts/qapi-types.py @@ -150,6 +150,14 @@ const int %(c_name)s_qtypes[QTYPE__MAX] = { 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 @@ -170,7 +178,7 @@ 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(''' diff --git a/qemu/scripts/qapi-visit.py b/qemu/scripts/qapi-visit.py index e2153393..343e7859 100644 --- a/qemu/scripts/qapi-visit.py +++ b/qemu/scripts/qapi-visit.py @@ -199,12 +199,15 @@ void visit_type_%(c_name)s(Visitor *v, const char *name, %(c_name)s *obj, Error def gen_visit_alternate(name, variants): + ret = '' promote_int = 'true' for var in variants.variants: if var.type.alternate_qtype() == 'QTYPE_QINT': promote_int = 'false' + if isinstance(var.type, QAPISchemaObjectType): + ret += gen_visit_fields_decl(var.type) - ret = mcgen(''' + ret += mcgen(''' void visit_type_%(c_name)s(Visitor *v, const char *name, %(c_name)s **obj, Error **errp) { @@ -220,17 +223,35 @@ void visit_type_%(c_name)s(Visitor *v, const char *name, %(c_name)s **obj, Error } switch ((*obj)->type) { ''', - c_name=c_name(name), promote_int=promote_int) + c_name=c_name(name), promote_int=promote_int) for var in variants.variants: ret += mcgen(''' case %(case)s: - visit_type_%(c_type)s(v, name, &(*obj)->u.%(c_name)s, &err); - break; ''', - case=var.type.alternate_qtype(), - c_type=var.type.c_name(), - c_name=c_name(var.name)) + case=var.type.alternate_qtype()) + if isinstance(var.type, QAPISchemaObjectType): + ret += mcgen(''' + visit_start_struct(v, name, NULL, 0, &err); + if (err) { + break; + } + visit_type_%(c_type)s_fields(v, &(*obj)->u.%(c_name)s, &err); + error_propagate(errp, err); + err = NULL; + visit_end_struct(v, &err); +''', + c_type=var.type.c_name(), + c_name=c_name(var.name)) + else: + ret += mcgen(''' + visit_type_%(c_type)s(v, name, &(*obj)->u.%(c_name)s, &err); +''', + c_type=var.type.c_name(), + c_name=c_name(var.name)) + ret += mcgen(''' + break; +''') ret += mcgen(''' default: diff --git a/qemu/scripts/qapi.py b/qemu/scripts/qapi.py index de0af39f..5da3ca23 100644 --- a/qemu/scripts/qapi.py +++ b/qemu/scripts/qapi.py @@ -827,7 +827,7 @@ class QAPISchemaVisitor(object): class QAPISchemaType(QAPISchemaEntity): - def c_type(self, is_param=False): + def c_type(self, is_param=False, is_unboxed=False): return c_name(self.name) + pointer_suffix def c_null(self): @@ -860,7 +860,7 @@ class QAPISchemaBuiltinType(QAPISchemaType): def c_name(self): return self.name - def c_type(self, is_param=False): + def c_type(self, is_param=False, is_unboxed=False): if is_param and self.name == 'str': return 'const ' + self._c_type_name return self._c_type_name @@ -894,7 +894,7 @@ class QAPISchemaEnumType(QAPISchemaType): # See QAPISchema._make_implicit_enum_type() return self.name.endswith('Kind') - def c_type(self, is_param=False): + def c_type(self, is_param=False, is_unboxed=False): return c_name(self.name) def member_names(self): @@ -991,9 +991,11 @@ class QAPISchemaObjectType(QAPISchemaType): assert not self.is_implicit() return QAPISchemaType.c_name(self) - def c_type(self, is_param=False): + def c_type(self, is_param=False, is_unboxed=False): assert not self.is_implicit() - return QAPISchemaType.c_type(self) + if is_unboxed: + return c_name(self.name) + return c_name(self.name) + pointer_suffix def json_type(self): return 'object'