[Qemu-devel] [PATCH v5 05/14] qapi: Emit implicit structs in generated C

[Eric Blake]

We already have several places that want to visit all the members
of an implicit object within a larger context (simple union variant,
event with anonymous data, command with anonymous arguments struct);
and will be adding another one soon (the ability to declare an
anonymous base for a flat union).  Having a C struct declared for
these implicit types, along with a visit_type_FOO_members() helper
function, will make for fewer special cases in our generator.

We do not, however, need qapi_free_FOO() or visit_type_FOO()
functions for implicit types, because they should not be used
directly outside of the generated code.  This is done by adding a
conditional in visit_object_type() for both qapi-types.py and
qapi-visit.py based on the object name.  The comparison of
"name.startswith('q_')" is a bit hacky (it's basically duplicating
what .is_implicit() already uses), but beats changing the signature
of the visit_object_type() callback to pass a new 'implicit' flag.
The hack should be temporary: we are considering adding a future
patch that consolidates the narrow visit_object_type() and
visit_object_type_flat() [with different pieces already broken out]
into a broader visit_object_type() [where the visitor can query the
type object directly].

Also, now that we WANT to output C code for implicits, we have to
change the condition in the visit_needed() filter.  We have to
special-case 'q_empty' in that filter as something that does not
get output: because it is a built-in type, it would be emitted in
multiple files (the main qapi-types.h and in qga-qapi-types.h)
causing compilation failure due to redefinition.  But since it
has no members, it's easier to just avoid an attempt to visit
that particular type.

The patch relies on the changed naming of implicit types in the
previous patch.  It is a bit unfortunate that the generated struct
names and visit_type_FOO_members() don't match normal naming
conventions, but it's not too bad, since they will only be used in
generated code.

The generated code grows substantially in size: the implicit
'-wrapper' types must be emitted in qapi-types.h before any union
can include an unboxed member of that type.  Arguably, the '-args'
types could be emitted in a private header for just qapi-visit.c
and qmp-marshal.c, rather than polluting qapi-types.h; but adding
complexity to the generator to split the output location according
to role doesn't seem worth the maintenance costs.  Another idea
for a later patch would be reworking error.h to not need to
include all of qapi-types.h.

Signed-off-by: Eric Blake <address@hidden>

---
v5: rebase onto different naming scheme, document future improvements
v4: new patch
---
 scripts/qapi.py       |  2 --
 scripts/qapi-types.py | 14 ++++++++------
 scripts/qapi-visit.py | 20 ++++++++++----------
 3 files changed, 18 insertions(+), 18 deletions(-)

diff --git a/scripts/qapi.py b/scripts/qapi.py
index f6701f5..96fb216 100644
--- a/scripts/qapi.py
+++ b/scripts/qapi.py
@@ -1000,7 +1000,6 @@ class QAPISchemaObjectType(QAPISchemaType):
         return self.name.startswith('q_')

     def c_name(self):
-        assert not self.is_implicit()
         return QAPISchemaType.c_name(self)

     def c_type(self):
@@ -1008,7 +1007,6 @@ class QAPISchemaObjectType(QAPISchemaType):
         return c_name(self.name) + pointer_suffix

     def c_unboxed_type(self):
-        assert not self.is_implicit()
         return c_name(self.name)

     def json_type(self):
diff --git a/scripts/qapi-types.py b/scripts/qapi-types.py
index f194bea..107eabe 100644
--- a/scripts/qapi-types.py
+++ b/scripts/qapi-types.py
@@ -61,8 +61,7 @@ def gen_object(name, base, members, variants):
     ret = ''
     if variants:
         for v in variants.variants:
-            if (isinstance(v.type, QAPISchemaObjectType) and
-                    not v.type.is_implicit()):
+            if isinstance(v.type, QAPISchemaObjectType):
                 ret += gen_object(v.type.name, v.type.base,
                                   v.type.local_members, v.type.variants)

@@ -197,9 +196,8 @@ class QAPISchemaGenTypeVisitor(QAPISchemaVisitor):
         self._btin = None

     def visit_needed(self, entity):
-        # Visit everything except implicit objects
-        return not (entity.is_implicit() and
-                    isinstance(entity, QAPISchemaObjectType))
+        # Visit everything except the special empty builtin
+        return entity.name != 'q_empty'

     def _gen_type_cleanup(self, name):
         self.decl += gen_type_cleanup_decl(name)
@@ -233,7 +231,11 @@ class QAPISchemaGenTypeVisitor(QAPISchemaVisitor):
         self.decl += gen_object(name, base, members, variants)
         if base:
             self.decl += gen_upcast(name, base)
-        self._gen_type_cleanup(name)
+        # FIXME Worth changing the visitor signature, so we could
+        # directly use rather than repeat type.is_implicit()?
+        if not name.startswith('q_'):
+            # implicit types won't be directly allocated/freed
+            self._gen_type_cleanup(name)

     def visit_alternate_type(self, name, info, variants):
         self._fwdecl += gen_fwd_object_or_array(name)
diff --git a/scripts/qapi-visit.py b/scripts/qapi-visit.py
index a712e9a..c486aaa 100644
--- a/scripts/qapi-visit.py
+++ b/scripts/qapi-visit.py
@@ -215,13 +215,11 @@ out:


 def gen_visit_object(name, base, members, variants):
-    ret = gen_visit_object_members(name, base, members, variants)
-
     # FIXME: if *obj is NULL on entry, and visit_start_struct() assigns to
     # *obj, but then visit_type_FOO_members() fails, we should clean up *obj
     # rather than leaving it non-NULL. As currently written, the caller must
     # call qapi_free_FOO() to avoid a memory leak of the partial FOO.
-    ret += mcgen('''
+    return mcgen('''

 void visit_type_%(c_name)s(Visitor *v, const char *name, %(c_name)s **obj, 
Error **errp)
 {
@@ -245,8 +243,6 @@ out:
 ''',
                  c_name=c_name(name))

-    return ret
-

 class QAPISchemaGenVisitVisitor(QAPISchemaVisitor):
     def __init__(self):
@@ -269,9 +265,8 @@ class QAPISchemaGenVisitVisitor(QAPISchemaVisitor):
         self._btin = None

     def visit_needed(self, entity):
-        # Visit everything except implicit objects
-        return not (entity.is_implicit() and
-                    isinstance(entity, QAPISchemaObjectType))
+        # Visit everything except the special empty builtin
+        return entity.name != 'q_empty'

     def visit_enum_type(self, name, info, values, prefix):
         # Special case for our lone builtin enum type
@@ -297,8 +292,13 @@ class QAPISchemaGenVisitVisitor(QAPISchemaVisitor):

     def visit_object_type(self, name, info, base, members, variants):
         self.decl += gen_visit_members_decl(name)
-        self.decl += gen_visit_decl(name)
-        self.defn += gen_visit_object(name, base, members, variants)
+        self.defn += gen_visit_object_members(name, base, members, variants)
+        # FIXME Worth changing the visitor signature, so we could
+        # directly use rather than repeat type.is_implicit()?
+        if not name.startswith('q_'):
+            # only explicit types need an allocating visit
+            self.decl += gen_visit_decl(name)
+            self.defn += gen_visit_object(name, base, members, variants)

     def visit_alternate_type(self, name, info, variants):
         self.decl += gen_visit_decl(name)
-- 
2.5.0