[Qemu-devel] [PATCH v7 28/31] qapi: Split visit_end_struct() into pieces

[Eric Blake <eblake@redhat.com>]

As mentioned in previous patches, we want to call visit_end_struct()
functions unconditionally, so that visitors can release resources
tied up since the matching visit_start_struct() without also having
to worry about error priority if more than one error occurs.

Even though error_propagate() can be safely used to ignore a second
error during cleanup caused by a first error, it is simpler if the
cleanup cannot set an error, and we instead split the task of
checking that an input visitor has no unvisited input as a new
function visit_check_struct(), called only if all prior steps are
successful.

Generated code has diffs resembling:

|@@ -59,10 +59,12 @@ void visit_type_ACPIOSTInfo(Visitor *v,
|         goto out_obj;
|     }
|     visit_type_ACPIOSTInfo_fields(v, obj, &err);
|+    if (err) {
|+        goto out_obj;
|+    }
|+    visit_check_struct(v, &err);
| out_obj:
|-    error_propagate(errp, err);
|-    err = NULL;
|-    visit_end_struct(v, &err);
|+    visit_end_struct(v);
| out:

Signed-off-by: Eric Blake <eblake@redhat.com>

---
v7: rebase to earlier changes
v6: new patch, revised version of RFC based on discussion of v5 7/46
---
 hmp.c                       |  7 ++++---
 hw/ppc/spapr_drc.c          |  3 ++-
 hw/virtio/virtio-balloon.c  | 12 ++++++------
 include/qapi/visitor-impl.h |  4 +++-
 include/qapi/visitor.h      | 13 ++++++++++---
 qapi/opts-visitor.c         | 17 +++++++++++++++--
 qapi/qapi-dealloc-visitor.c |  2 +-
 qapi/qapi-visit-core.c      | 11 +++++++++--
 qapi/qmp-input-visitor.c    | 34 +++++++++++++++++++---------------
 qapi/qmp-output-visitor.c   |  2 +-
 qom/object.c                |  5 ++---
 scripts/qapi-event.py       |  3 ++-
 scripts/qapi-visit.py       |  9 ++++-----
 vl.c                        | 11 +++++------
 14 files changed, 83 insertions(+), 50 deletions(-)

diff --git a/hmp.c b/hmp.c
index f81f332..35cd625 100644
--- a/hmp.c
+++ b/hmp.c
@@ -1698,13 +1698,14 @@ void hmp_object_add(Monitor *mon, const QDict *qdict)
     }

     object_add(type, id, pdict, v, &err);
-
-out_end:
-    visit_end_struct(v, &err_end);
+    visit_check_struct(v, &err_end);
     if (!err && err_end) {
         qmp_object_del(id, NULL);
     }
     error_propagate(&err, err_end);
+
+out_end:
+    visit_end_struct(v);
 out_clean:
     opts_visitor_cleanup(ov);

diff --git a/hw/ppc/spapr_drc.c b/hw/ppc/spapr_drc.c
index 0c675ff..65764bc 100644
--- a/hw/ppc/spapr_drc.c
+++ b/hw/ppc/spapr_drc.c
@@ -287,11 +287,12 @@ static void prop_get_fdt(Object *obj, Visitor *v, void *opaque,
         case FDT_END_NODE:
             /* shouldn't ever see an FDT_END_NODE before FDT_BEGIN_NODE */
             g_assert(fdt_depth > 0);
-            visit_end_struct(v, &err);
+            visit_check_struct(v, &err);
             if (err) {
                 error_propagate(errp, err);
                 return;
             }
+            visit_end_struct(v);
             fdt_depth--;
             break;
         case FDT_PROP: {
diff --git a/hw/virtio/virtio-balloon.c b/hw/virtio/virtio-balloon.c
index cb8237f..fc3bced 100644
--- a/hw/virtio/virtio-balloon.c
+++ b/hw/virtio/virtio-balloon.c
@@ -136,15 +136,15 @@ static void balloon_stats_get_all(Object *obj, struct Visitor *v,
             goto out_nested;
         }
     }
+    visit_check_struct(v, &err);
 out_nested:
-    error_propagate(errp, err);
-    err = NULL;
-    visit_end_struct(v, &err);
+    visit_end_struct(v);

+    if (!err) {
+        visit_check_struct(v, &err);
+    }
 out_end:
-    error_propagate(errp, err);
-    err = NULL;
-    visit_end_struct(v, &err);
+    visit_end_struct(v);
 out:
     error_propagate(errp, err);
 }
diff --git a/include/qapi/visitor-impl.h b/include/qapi/visitor-impl.h
index 3b67dc7..d1f4f78 100644
--- a/include/qapi/visitor-impl.h
+++ b/include/qapi/visitor-impl.h
@@ -28,8 +28,10 @@ struct Visitor
      * currently visit structs). */
     void (*start_struct)(Visitor *v, void **obj, size_t size,
                          const char *name, Error **errp);
+    /* May be NULL; most useful for input visitors. */
+    void (*check_struct)(Visitor *v, Error **errp);
     /* Must be provided if start_struct is present. */
-    void (*end_struct)(Visitor *v, Error **errp);
+    void (*end_struct)(Visitor *v);

     /* May be NULL; most useful for input visitors. */
     void (*start_implicit_struct)(Visitor *v, void **obj, size_t size,
diff --git a/include/qapi/visitor.h b/include/qapi/visitor.h
index b8146d7..f83707a 100644
--- a/include/qapi/visitor.h
+++ b/include/qapi/visitor.h
@@ -68,12 +68,19 @@ typedef struct GenericList
 void visit_start_struct(Visitor *v, void **obj, size_t size,
                         const char *name, Error **errp);
 /**
+ * Prepare for completing a struct visit.
+ * Should be called prior to visit_end_struct() if all other intermediate
+ * visit steps were successful, to allow the caller one last chance to
+ * report errors such as remaining data that was not consumed by the visit.
+ */
+void visit_check_struct(Visitor *v, Error **errp);
+/**
  * Complete a struct visit started earlier.
  * 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.
  */
-void visit_end_struct(Visitor *v, Error **errp);
+void visit_end_struct(Visitor *v);

 /**
  * Prepare to visit an implicit struct.
@@ -96,8 +103,8 @@ void visit_start_implicit_struct(Visitor *v, void **obj, size_t size,
  * Must be called after any successful use of visit_start_implicit_struct(),
  * even if intermediate processing was skipped due to errors, to allow
  * the backend to release any resources.  Unlike visit_end_struct(), this
- * does not need to check for errors (detection of unused keys is only
- * possible for the overall struct, not a subset).
+ * does not need a counterpart function to check for errors (detection of
+ * unused keys is only possible for the overall struct, not a subset).
  */
 void visit_end_implicit_struct(Visitor *v);

diff --git a/qapi/opts-visitor.c b/qapi/opts-visitor.c
index a767391..fabf3d7 100644
--- a/qapi/opts-visitor.c
+++ b/qapi/opts-visitor.c
@@ -157,13 +157,13 @@ opts_start_struct(Visitor *v, void **obj, size_t size,


 static void
-opts_end_struct(Visitor *v, Error **errp)
+opts_check_struct(Visitor *v, Error **errp)
 {
     OptsVisitor *ov = to_ov(v);
     GHashTableIter iter;
     GQueue *any;

-    if (--ov->depth > 0) {
+    if (ov->depth > 0) {
         return;
     }

@@ -175,6 +175,18 @@ opts_end_struct(Visitor *v, Error **errp)
         first = g_queue_peek_head(any);
         error_setg(errp, QERR_INVALID_PARAMETER, first->name);
     }
+}
+
+
+static void
+opts_end_struct(Visitor *v)
+{
+    OptsVisitor *ov = DO_UPCAST(OptsVisitor, visitor, v);
+
+    if (--ov->depth > 0) {
+        return;
+    }
+
     g_hash_table_destroy(ov->unprocessed_opts);
     ov->unprocessed_opts = NULL;
     if (ov->fake_id_opt) {
@@ -506,6 +518,7 @@ opts_visitor_new(const QemuOpts *opts)
     ov = g_malloc0(sizeof *ov);

     ov->visitor.start_struct = &opts_start_struct;
+    ov->visitor.check_struct = &opts_check_struct;
     ov->visitor.end_struct   = &opts_end_struct;

     ov->visitor.start_list = &opts_start_list;
diff --git a/qapi/qapi-dealloc-visitor.c b/qapi/qapi-dealloc-visitor.c
index 92345aa..d3f9171 100644
--- a/qapi/qapi-dealloc-visitor.c
+++ b/qapi/qapi-dealloc-visitor.c
@@ -65,7 +65,7 @@ static void qapi_dealloc_start_struct(Visitor *v, void **obj, size_t unused,
     qapi_dealloc_push(qov, obj);
 }

-static void qapi_dealloc_end_struct(Visitor *v, Error **errp)
+static void qapi_dealloc_end_struct(Visitor *v)
 {
     QapiDeallocVisitor *qov = to_qov(v);
     void **obj = qapi_dealloc_pop(qov);
diff --git a/qapi/qapi-visit-core.c b/qapi/qapi-visit-core.c
index 09cc5c9..a3b59f7 100644
--- a/qapi/qapi-visit-core.c
+++ b/qapi/qapi-visit-core.c
@@ -36,9 +36,16 @@ void visit_start_struct(Visitor *v, void **obj, size_t size,
     v->start_struct(v, obj, size, name, errp);
 }

-void visit_end_struct(Visitor *v, Error **errp)
+void visit_check_struct(Visitor *v, Error **errp)
 {
-    v->end_struct(v, errp);
+    if (v->check_struct) {
+        v->check_struct(v, errp);
+    }
+}
+
+void visit_end_struct(Visitor *v)
+{
+    v->end_struct(v);
 }

 void visit_start_implicit_struct(Visitor *v, void **obj, size_t size,
diff --git a/qapi/qmp-input-visitor.c b/qapi/qmp-input-visitor.c
index 0587b8e..18c963b 100644
--- a/qapi/qmp-input-visitor.c
+++ b/qapi/qmp-input-visitor.c
@@ -89,8 +89,10 @@ static void qmp_input_push(QmpInputVisitor *qiv, QObject *obj, Error **errp)
 }


-static void qmp_input_pop(QmpInputVisitor *qiv, Error **errp)
+static void qmp_input_check_struct(Visitor *v, Error **errp)
 {
+    QmpInputVisitor *qiv = to_qiv(v);
+
     assert(qiv->nb_stack > 0);

     if (qiv->strict) {
@@ -103,6 +105,19 @@ static void qmp_input_pop(QmpInputVisitor *qiv, Error **errp)
             if (g_hash_table_iter_next(&iter, (void **)&key, NULL)) {
                 error_setg(errp, QERR_QMP_EXTRA_MEMBER, key);
             }
+        }
+    }
+}
+
+static void qmp_input_pop(Visitor *v)
+{
+    QmpInputVisitor *qiv = to_qiv(v);
+
+    assert(qiv->nb_stack > 0);
+
+    if (qiv->strict) {
+        GHashTable * const top_ht = qiv->stack[qiv->nb_stack - 1].h;
+        if (top_ht) {
             g_hash_table_unref(top_ht);
         }
     }
@@ -134,12 +149,6 @@ static void qmp_input_start_struct(Visitor *v, void **obj, size_t size,
     }
 }

-static void qmp_input_end_struct(Visitor *v, Error **errp)
-{
-    QmpInputVisitor *qiv = to_qiv(v);
-
-    qmp_input_pop(qiv, errp);
-}

 static void qmp_input_start_implicit_struct(Visitor *v, void **obj,
                                             size_t size, Error **errp)
@@ -193,12 +202,6 @@ static GenericList *qmp_input_next_list(Visitor *v, GenericList **list,
     return entry;
 }

-static void qmp_input_end_list(Visitor *v)
-{
-    QmpInputVisitor *qiv = to_qiv(v);
-
-    qmp_input_pop(qiv, &error_abort);
-}

 static void qmp_input_get_next_type(Visitor *v, QType *type, bool promote_int,
                                     const char *name, Error **errp)
@@ -342,11 +345,12 @@ QmpInputVisitor *qmp_input_visitor_new(QObject *obj)
     v = g_malloc0(sizeof(*v));

     v->visitor.start_struct = qmp_input_start_struct;
-    v->visitor.end_struct = qmp_input_end_struct;
+    v->visitor.check_struct = qmp_input_check_struct;
+    v->visitor.end_struct = qmp_input_pop;
     v->visitor.start_implicit_struct = qmp_input_start_implicit_struct;
     v->visitor.start_list = qmp_input_start_list;
     v->visitor.next_list = qmp_input_next_list;
-    v->visitor.end_list = qmp_input_end_list;
+    v->visitor.end_list = qmp_input_pop;
     v->visitor.type_enum = input_type_enum;
     v->visitor.type_int64 = qmp_input_type_int64;
     v->visitor.type_uint64 = qmp_input_type_uint64;
diff --git a/qapi/qmp-output-visitor.c b/qapi/qmp-output-visitor.c
index 28f9854..1ffe820 100644
--- a/qapi/qmp-output-visitor.c
+++ b/qapi/qmp-output-visitor.c
@@ -117,7 +117,7 @@ static void qmp_output_start_struct(Visitor *v, void **obj, size_t unused,
     qmp_output_push(qov, dict);
 }

-static void qmp_output_end_struct(Visitor *v, Error **errp)
+static void qmp_output_end_struct(Visitor *v)
 {
     QmpOutputVisitor *qov = to_qov(v);
     qmp_output_pop(qov);
diff --git a/qom/object.c b/qom/object.c
index 5eb65ea..36de3a2 100644
--- a/qom/object.c
+++ b/qom/object.c
@@ -1904,10 +1904,9 @@ static void property_get_tm(Object *obj, Visitor *v, void *opaque,
     if (err) {
         goto out_end;
     }
+    visit_check_struct(v, &err);
 out_end:
-    error_propagate(errp, err);
-    err = NULL;
-    visit_end_struct(v, errp);
+    visit_end_struct(v);
 out:
     error_propagate(errp, err);

diff --git a/scripts/qapi-event.py b/scripts/qapi-event.py
index 6a29b6c..83f1257 100644
--- a/scripts/qapi-event.py
+++ b/scripts/qapi-event.py
@@ -71,8 +71,9 @@ def gen_event_send(name, arg_type):
         ret += gen_visit_fields(arg_type.members, need_cast=True,
                                 label='out_obj')
         ret += mcgen('''
+    visit_check_struct(v, &err);
 out_obj:
-    visit_end_struct(v, &err);
+    visit_end_struct(v);
     if (err) {
         goto out;
     }
diff --git a/scripts/qapi-visit.py b/scripts/qapi-visit.py
index 5c8f1e6..694951f 100644
--- a/scripts/qapi-visit.py
+++ b/scripts/qapi-visit.py
@@ -255,8 +255,7 @@ void visit_type_%(c_name)s(Visitor *v, %(c_name)s **obj, const char *name, Error
     visit_type_%(c_name)s_fields(v, %(cast)sobj, &err);
 ''',
                      c_name=type_name, cast=cast)
-        if variants:
-            ret += gen_err_check(label='out_obj')
+        ret += gen_err_check(label='out_obj')

     if variants:
         ret += mcgen('''
@@ -293,12 +292,12 @@ void visit_type_%(c_name)s(Visitor *v, %(c_name)s **obj, const char *name, Error
         abort();
     }
 ''')
+        ret += gen_err_check(label='out_obj')

     ret += mcgen('''
+    visit_check_struct(v, &err);
 out_obj:
-    error_propagate(errp, err);
-    err = NULL;
-    visit_end_struct(v, &err);
+    visit_end_struct(v);
 out:
     error_propagate(errp, err);
 }
diff --git a/vl.c b/vl.c
index 1010bdb..ed1203e 100644
--- a/vl.c
+++ b/vl.c
@@ -2848,11 +2848,10 @@ static int object_create(void *opaque, QemuOpts *opts, Error **errp)
     qdict_del(pdict, "qom-type");
     visit_type_str(v, &type, "qom-type", &err);
     if (err) {
-        goto out;
+        goto out_end;
     }
     if (!type_predicate(type)) {
-        visit_end_struct(v, NULL);
-        goto out;
+        goto out_end;
     }

     qdict_del(pdict, "id");
@@ -2862,14 +2861,14 @@ static int object_create(void *opaque, QemuOpts *opts, Error **errp)
     }

     object_add(type, id, pdict, v, &err);
-
-out_end:
-    visit_end_struct(v, &err_end);
+    visit_check_struct(v, &err_end);
     if (!err && err_end) {
         qmp_object_del(id, NULL);
     }
     error_propagate(&err, err_end);

+out_end:
+    visit_end_struct(v);
 out:
     opts_visitor_cleanup(ov);

-- 
2.4.3