[Qemu-devel] [PATCH v12 14/18] qapi-commands: Wrap argument visit in visit_start_struct

[Eric Blake <eblake@redhat.com>]

The qmp-input visitor was playing rather fast and loose: when
visiting a QDict, you could grab members of the root dictionary
without first pushing into the dict.  But we are about to tighten
the input visitor, at which point the generated marshal code
MUST follow the same paradigms as everyone else, of pushing into
the struct before grabbing its keys, because the value of 'name'
should be ignored on the top-level visit.

It will also make things easier to follow when we introduce boxed
command parameters, where we call visit_type_FOO() instead of
individual members of FOO, since visit_type_FOO() also uses a
level of visit_start_struct() for handling the same QDict input.

Generated code grows as follows:

|@@ -63,18 +63,28 @@ void qmp_marshal_add_fd(QDict *args, QOb
|     char *opaque = NULL;
|
|     v = qmp_input_get_visitor(qiv);
|+    visit_start_struct(v, NULL, NULL, 0, &err);
|+    if (err) {
|+        goto out;
|+    }
|     if (visit_optional(v, "fdset-id", &has_fdset_id)) {
|         visit_type_int(v, "fdset-id", &fdset_id, &err);
|         if (err) {
|-            goto out;
|+            goto out_obj;
|         }
|     }
|     if (visit_optional(v, "opaque", &has_opaque)) {
|         visit_type_str(v, "opaque", &opaque, &err);
|         if (err) {
|-            goto out;
|+            goto out_obj;
|         }
|     }
|+    visit_check_struct(v, &err);
|+out_obj:
|+    visit_end_struct(v);
|+    if (err) {
|+        goto out;
|+    }
|
|     retval = qmp_add_fd(has_fdset_id, fdset_id, has_opaque, opaque, &err);

Note that this change could also make it possible for the
marshalling code to automatically detect excess input at the top
level, and not just in nested dictionaries.  However, that checking
is not currently useful (and we rely on the manual checking in
monitor.c:qmp_check_client_args() instead) as long as qmp-commands.hx
uses .args_type, and as long as we have 'name:O' as an arg-type that
explicitly allows unknown top-level keys because we haven't yet
converted 'device_add' and 'netdev_add' to introspectible use of
'any'.

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

---
v12: new patch
---
 scripts/qapi-commands.py | 16 +++++++++++++++-
 1 file changed, 15 insertions(+), 1 deletion(-)

diff --git a/scripts/qapi-commands.py b/scripts/qapi-commands.py
index 7c9cfbf..a586676 100644
--- a/scripts/qapi-commands.py
+++ b/scripts/qapi-commands.py
@@ -109,14 +109,28 @@ def gen_marshal_input_visit(arg_type, dealloc=False):
     else:
         ret += mcgen('''
     v = qmp_input_get_visitor(qiv);
+    visit_start_struct(v, NULL, NULL, 0, &err);
+    if (err) {
+        goto out;
+    }
 ''')

-    ret += gen_visit_members(arg_type.members, skiperr=dealloc)
+    ret += gen_visit_members(arg_type.members, skiperr=dealloc,
+                             label='out_obj')

     if dealloc:
         ret += mcgen('''
     qapi_dealloc_visitor_cleanup(qdv);
 ''')
+    else:
+        ret += mcgen('''
+    visit_check_struct(v, &err);
+out_obj:
+    visit_end_struct(v);
+    if (err) {
+        goto out;
+    }
+''')
     return ret


-- 
2.5.0