[Qemu-devel] [PATCH v6 22/23] 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.

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

---
v6: new patch, revised version of RFC based on discussion of v5 7/46
---
 hmp.c                       |  8 +++-----
 hw/ppc/spapr_drc.c          |  3 ++-
 hw/virtio/virtio-balloon.c  | 12 ++++++------
 include/qapi/visitor-impl.h |  4 +++-
 include/qapi/visitor.h      | 12 ++++++++++--
 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                        |  9 ++++-----
 14 files changed, 81 insertions(+), 50 deletions(-)

diff --git a/hmp.c b/hmp.c
index ec1d682..b09f78b 100644
--- a/hmp.c
+++ b/hmp.c
@@ -1663,7 +1663,6 @@ void hmp_netdev_del(Monitor *mon, const QDict *qdict)
 void hmp_object_add(Monitor *mon, const QDict *qdict)
 {
     Error *err = NULL;
-    Error *err_end = NULL;
     QemuOpts *opts;
     char *type = NULL;
     char *id = NULL;
@@ -1696,13 +1695,12 @@ void hmp_object_add(Monitor *mon, const QDict *qdict)
     if (err) {
         goto out_end;
     }
-
+    visit_check_struct(v, &err);
 out_end:
-    visit_end_struct(v, &err_end);
-    if (!err && !err_end) {
+    visit_end_struct(v);
+    if (!err) {
         object_add(type, id, pdict, v, &err);
     }
-    error_propagate(&err, err_end);
 out_clean:
     opts_visitor_cleanup(ov);

diff --git a/hw/ppc/spapr_drc.c b/hw/ppc/spapr_drc.c
index 03a1879..5ff270f 100644
--- a/hw/ppc/spapr_drc.c
+++ b/hw/ppc/spapr_drc.c
@@ -281,7 +281,8 @@ 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, &error_abort);
+            visit_check_struct(v, &error_abort);
+            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 1ce987a..531913b 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 018f419..5350bdf 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, const char *kind,
                          const char *name, size_t size, 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 cc1ff6d..f9ea325 100644
--- a/include/qapi/visitor.h
+++ b/include/qapi/visitor.h
@@ -57,11 +57,19 @@ typedef struct GenericList
 void visit_start_struct(Visitor *v, void **obj, const char *kind,
                         const char *name, size_t size, 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.
+ * 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.
diff --git a/qapi/opts-visitor.c b/qapi/opts-visitor.c
index 46dd9fe..db5fc1a 100644
--- a/qapi/opts-visitor.c
+++ b/qapi/opts-visitor.c
@@ -151,13 +151,13 @@ opts_start_struct(Visitor *v, void **obj, const char *kind,


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

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

@@ -169,6 +169,18 @@ 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) {
@@ -500,6 +512,7 @@ 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 8b489a4..14dc7c3 100644
--- a/qapi/qapi-dealloc-visitor.c
+++ b/qapi/qapi-dealloc-visitor.c
@@ -67,7 +67,7 @@ static void qapi_dealloc_start_struct(Visitor *v, void **obj, const char *kind,
     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 a193a04..00f446e 100644
--- a/qapi/qapi-visit-core.c
+++ b/qapi/qapi-visit-core.c
@@ -23,9 +23,16 @@ void visit_start_struct(Visitor *v, void **obj, const char *kind,
     v->start_struct(v, obj, kind, name, size, 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 9dbe025..0270d25 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, const char *kind,
     }
 }

-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)
@@ -341,11 +344,12 @@ 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 8035649..af1e01b 100644
--- a/qapi/qmp-output-visitor.c
+++ b/qapi/qmp-output-visitor.c
@@ -122,7 +122,7 @@ static void qmp_output_start_struct(Visitor *v, void **obj, const char *kind,
     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 d751569..3d5c9d7 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 7ee74a5..68d59e1 100644
--- a/scripts/qapi-event.py
+++ b/scripts/qapi-event.py
@@ -74,8 +74,9 @@ 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 43233d6..c28208e 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 4e69815..32e4300 100644
--- a/vl.c
+++ b/vl.c
@@ -2828,7 +2828,6 @@ static bool object_create_delayed(const char *type)
 static int object_create(void *opaque, QemuOpts *opts, Error **errp)
 {
     Error *err = NULL;
-    Error *err_end = NULL;
     char *type = NULL;
     char *id = NULL;
     OptsVisitor *ov;
@@ -2848,7 +2847,7 @@ 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)) {
         goto out_end;
@@ -2859,10 +2858,10 @@ static int object_create(void *opaque, QemuOpts *opts, Error **errp)
     if (err) {
         goto out_end;
     }
-
+    visit_check_struct(v, &err);
 out_end:
-    visit_end_struct(v, &err_end);
-    if (!err && !err_end) {
+    visit_end_struct(v);
+    if (!err) {
         object_add(type, id, pdict, v, &err);
     }

-- 
2.4.3