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[Qemu-devel] [PATCH v4 04/10] qapi: Emit implicit structs in generated C

From: Eric Blake
Subject: [Qemu-devel] [PATCH v4 04/10] qapi: Emit implicit structs in generated C
Date: Sat, 5 Mar 2016 09:16:29 -0700

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[0] == ':'" feels a bit hacky, but beats changing the
signature of the visit_object_type() callback to pass a new
'implicit' flag.  Also, now that we WANT to output C code for
implicits, we have to change the condition in the visit_needed()

We have to special-case ':empty' 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 fact that all our implicit objects start
with a leading ':', which can be transliteratated to a leading
single underscore, and we've already documented and enforce that
the user can't create QAPI names with a leading underscore, so
exposing the types won't create any collisions.  It is a bit
unfortunate that the generated struct names 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; in part because
it was easier to output every implicit type rather than adding
generator complexity to try and only output types as needed.

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

v4: new patch
 scripts/qapi.py       |  3 +--
 scripts/qapi-types.py | 12 ++++++------
 scripts/qapi-visit.py | 18 ++++++++----------
 3 files changed, 15 insertions(+), 18 deletions(-)

diff --git a/scripts/qapi.py b/scripts/qapi.py
index b1b87ee..6cf0a75 100644
--- a/scripts/qapi.py
+++ b/scripts/qapi.py
@@ -999,7 +999,6 @@ class QAPISchemaObjectType(QAPISchemaType):
         return self.name[0] == ':'

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

     def c_type(self):
@@ -1476,7 +1475,7 @@ def c_enum_const(type_name, const_name, prefix=None):
         type_name = prefix
     return camel_to_upper(type_name) + '_' + c_name(const_name, False).upper()

-c_name_trans = string.maketrans('.-', '__')
+c_name_trans = string.maketrans('.-:', '___')

 # Map @name to a valid C identifier.
diff --git a/scripts/qapi-types.py b/scripts/qapi-types.py
index f194bea..fa2d6af 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 != ':empty'

     def _gen_type_cleanup(self, name):
         self.decl += gen_type_cleanup_decl(name)
@@ -233,7 +231,9 @@ class QAPISchemaGenTypeVisitor(QAPISchemaVisitor):
         self.decl += gen_object(name, base, members, variants)
         if base:
             self.decl += gen_upcast(name, base)
-        self._gen_type_cleanup(name)
+        if name[0] != ':':
+            # 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..b4303a7 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:

-    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 != ':empty'

     def visit_enum_type(self, name, info, values, prefix):
         # Special case for our lone builtin enum type
@@ -297,8 +292,11 @@ 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)
+        if name[0] != ':':
+            # 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)

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