diff options
Diffstat (limited to 'include/qapi')
| -rw-r--r-- | include/qapi/visitor.h | 25 |
1 files changed, 16 insertions, 9 deletions
diff --git a/include/qapi/visitor.h b/include/qapi/visitor.h index 8de6b436fb..4d12167bdc 100644 --- a/include/qapi/visitor.h +++ b/include/qapi/visitor.h @@ -66,12 +66,14 @@ * member @name is not present, or is present but not the specified * type). * - * FIXME: At present, visit_type_FOO() is an awkward interface: input - * visitors may allocate an incomplete *@obj even when reporting an - * error, but using an output visitor with an incomplete object has - * undefined behavior. To avoid a memory leak, callers must use - * qapi_free_FOO() even on error (this uses the dealloc visitor, and - * safely handles an incomplete object). + * If an error is detected during visit_type_FOO() with an input + * visitor, then *@obj will be NULL for pointer types, and left + * unchanged for scalar types. Using an output visitor with an + * incomplete object has undefined behavior (other than a special case + * for visit_type_str() treating NULL like ""), while the dealloc + * visitor safely handles incomplete objects. Since input visitors + * never produce an incomplete object, such an object is possible only + * by manual construction. * * For the QAPI object types (structs, unions, and alternates), there * is an additional generated function in qapi-visit.h compatible @@ -106,7 +108,6 @@ * v = ...obtain input visitor... * visit_type_Foo(v, NULL, &f, &err); * if (err) { - * qapi_free_Foo(f); * ...handle error... * } else { * ...use f... @@ -124,7 +125,6 @@ * v = ...obtain input visitor... * visit_type_FooList(v, NULL, &l, &err); * if (err) { - * qapi_free_FooList(l); * ...handle error... * } else { * for ( ; l; l = l->next) { @@ -154,7 +154,9 @@ * helpers that rely on in-tree information to control the walk: * visit_optional() for the 'has_member' field associated with * optional 'member' in the C struct; and visit_next_list() for - * advancing through a FooList linked list. Only the generated + * advancing through a FooList linked list. Similarly, the + * visit_is_input() helper makes it possible to write code that is + * visitor-agnostic everywhere except for cleanup. Only the generated * visit_type functions need to use these helpers. * * It is also possible to use the visitors to do a virtual walk, where @@ -405,6 +407,11 @@ bool visit_optional(Visitor *v, const char *name, bool *present); void visit_type_enum(Visitor *v, const char *name, int *obj, const char *const strings[], Error **errp); +/* + * Check if visitor is an input visitor. + */ +bool visit_is_input(Visitor *v); + /*** Visiting built-in types ***/ /* |