qapi: Add parameter to visit_end_*

Rather than making the dealloc visitor track of stack of pointers
remembered during visit_start_* in order to free them during
visit_end_*, it's a lot easier to just make all callers pass the
same pointer to visit_end_*.  The generated code has access to the
same pointer, while all other users are doing virtual walks and
can pass NULL.  The dealloc visitor is then greatly simplified.

All three visit_end_*() functions intentionally take a void**,
even though the visit_start_*() functions differ between void**,
GenericList**, and GenericAlternate**.  This is done for several
reasons: when doing a virtual walk, passing NULL doesn't care
what the type is, but when doing a generated walk, we already
have to cast the caller's specific FOO* to call visit_start,
while using void** lets us use visit_end without a cast. Also,
an upcoming patch will add a clone visitor that wants to use
the same implementation for all three visit_end callbacks,
which is made easier if all three share the same signature.

For visitors with already track per-object state (the QMP visitors
via a stack, and the string visitors which do not allow nesting),
add an assertion that the caller is indeed passing the same
pointer to paired calls.

Signed-off-by: Eric Blake <eblake@redhat.com>
Message-Id: <1465490926-28625-4-git-send-email-eblake@redhat.com>
Reviewed-by: Markus Armbruster <armbru@redhat.com>
Signed-off-by: Markus Armbruster <armbru@redhat.com>

2 files changed, 22 insertions, 16 deletions

diff --git a/include/qapi/visitor-impl.h b/include/qapi/visitor-impl.h
index 145afd0..a495bf0 100644
--- a/include/qapi/visitor-impl.h
+++ b/include/qapi/visitor-impl.h
@@ -47,7 +47,7 @@ struct Visitor
     void (*check_struct)(Visitor *v, Error **errp);
 
     /* Must be set to visit structs */
-    void (*end_struct)(Visitor *v);
+    void (*end_struct)(Visitor *v, void **obj);
 
     /* Must be set; implementations may require @list to be non-null,
      * but must document it. */
@@ -58,7 +58,7 @@ struct Visitor
     GenericList *(*next_list)(Visitor *v, GenericList *tail, size_t size);
 
     /* Must be set */
-    void (*end_list)(Visitor *v);
+    void (*end_list)(Visitor *v, void **list);
 
     /* Must be set by input and dealloc visitors to visit alternates;
      * optional for output visitors. */
@@ -67,7 +67,7 @@ struct Visitor
                             bool promote_int, Error **errp);
 
     /* Optional, needed for dealloc visitor */
-    void (*end_alternate)(Visitor *v);
+    void (*end_alternate)(Visitor *v, void **obj);
 
     /* Must be set */
     void (*type_int64)(Visitor *v, const char *name, int64_t *obj,
diff --git a/include/qapi/visitor.h b/include/qapi/visitor.h
index 4d12167..25d0cc2 100644
--- a/include/qapi/visitor.h
+++ b/include/qapi/visitor.h
@@ -193,12 +193,12 @@
  *      goto outlist;
  *  }
  * outlist:
- *  visit_end_list(v);
+ *  visit_end_list(v, NULL);
  *  if (!err) {
  *      visit_check_struct(v, &err);
  *  }
  * outobj:
- *  visit_end_struct(v);
+ *  visit_end_struct(v, NULL);
  * out:
  *  error_propagate(errp, err);
  *  ...clean up v...
@@ -242,8 +242,8 @@ typedef struct GenericAlternate {
  * After visit_start_struct() succeeds, the caller may visit its
  * members one after the other, passing the member's name and address
  * within the struct.  Finally, visit_end_struct() needs to be called
- * to clean up, even if intermediate visits fail.  See the examples
- * above.
+ * with the same @obj to clean up, even if intermediate visits fail.
+ * See the examples above.
  *
  * FIXME Should this be named visit_start_object, since it is also
  * used for QAPI unions, and maps to JSON objects?
@@ -267,12 +267,14 @@ void visit_check_struct(Visitor *v, Error **errp);
 /*
  * Complete an object visit started earlier.
  *
+ * @obj must match what was passed to the paired visit_start_struct().
+ *
  * Must be called after any successful use of visit_start_struct(),
  * even if intermediate processing was skipped due to errors, to allow
  * the backend to release any resources.  Destroying the visitor early
  * behaves as if this was implicitly called.
  */
-void visit_end_struct(Visitor *v);
+void visit_end_struct(Visitor *v, void **obj);
 
 
 /*** Visiting lists ***/
@@ -299,8 +301,9 @@ void visit_end_struct(Visitor *v);
  * visit (where @obj is NULL) uses other means.  For each list
  * element, call the appropriate visit_type_FOO() with name set to
  * NULL and obj set to the address of the value member of the list
- * element.  Finally, visit_end_list() needs to be called to clean up,
- * even if intermediate visits fail.  See the examples above.
+ * element.  Finally, visit_end_list() needs to be called with the
+ * same @list to clean up, even if intermediate visits fail.  See the
+ * examples above.
  */
 void visit_start_list(Visitor *v, const char *name, GenericList **list,
                       size_t size, Error **errp);
@@ -324,12 +327,14 @@ GenericList *visit_next_list(Visitor *v, GenericList *tail, size_t size);
 /*
  * Complete a list visit started earlier.
  *
+ * @list must match what was passed to the paired visit_start_list().
+ *
  * Must be called after any successful use of visit_start_list(), even
  * if intermediate processing was skipped due to errors, to allow the
  * backend to release any resources.  Destroying the visitor early
  * behaves as if this was implicitly called.
  */
-void visit_end_list(Visitor *v);
+void visit_end_list(Visitor *v, void **list);
 
 
 /*** Visiting alternates ***/
@@ -347,8 +352,9 @@ void visit_end_list(Visitor *v);
  *
  * If @promote_int, treat integers as QTYPE_FLOAT.
  *
- * If successful, this must be paired with visit_end_alternate() to
- * clean up, even if visiting the contents of the alternate fails.
+ * If successful, this must be paired with visit_end_alternate() with
+ * the same @obj to clean up, even if visiting the contents of the
+ * alternate fails.
  */
 void visit_start_alternate(Visitor *v, const char *name,
                            GenericAlternate **obj, size_t size,
@@ -357,15 +363,15 @@ void visit_start_alternate(Visitor *v, const char *name,
 /*
  * Finish visiting an alternate type.
  *
+ * @obj must match what was passed to the paired visit_start_alternate().
+ *
  * Must be called after any successful use of visit_start_alternate(),
  * even if intermediate processing was skipped due to errors, to allow
  * the backend to release any resources.  Destroying the visitor early
  * behaves as if this was implicitly called.
  *
- * TODO: Should all the visit_end_* interfaces take obj parameter, so
- * that dealloc visitor need not track what was passed in visit_start?
  */
-void visit_end_alternate(Visitor *v);
+void visit_end_alternate(Visitor *v, void **obj);
 
 
 /*** Other helpers ***/