Re: [Qemu-devel] [PATCH v5 07/14] qapi: Utilize implicit struct visits

[Markus Armbruster]

Here's how I'd rebase this on the simplified PATCH 06 I just posted as a
reply to yours:

>From e35449172828351f0acd85f236add45d3eb575a7 Mon Sep 17 00:00:00 2001
From: Eric Blake <address@hidden>
Date: Wed, 9 Mar 2016 17:55:28 -0700
Subject: [PATCH 07/14] qapi: Utilize implicit struct visits

Rather than generate inline per-member visits, take advantage
of the 'visit_type_FOO_members()' function for both event and
command marshalling.  This is possible now that implicit
structs can be visited like any other.

Generated code shrinks accordingly; events initialize a struct
based on parameters, through a new gen_param_var() helper, like:

|@@ -338,6 +250,9 @@ void qapi_event_send_block_job_error(con
|     QMPEventFuncEmit emit = qmp_event_get_func_emit();
|     QmpOutputVisitor *qov;
|     Visitor *v;
|+    q_obj_BLOCK_JOB_ERROR_arg param = {
|+        (char *)device, operation, action
|+    };
|
|     if (!emit) {
|         return;
@@ -351,19 +266,7 @@ void qapi_event_send_block_job_error(con
|     if (err) {
|         goto out;
|     }
|-    visit_type_str(v, "device", (char **)&device, &err);
|-    if (err) {
|-        goto out_obj;
|-    }
|-    visit_type_IoOperationType(v, "operation", &operation, &err);
|-    if (err) {
|-        goto out_obj;
|-    }
|-    visit_type_BlockErrorAction(v, "action", &action, &err);
|-    if (err) {
|-        goto out_obj;
|-    }
|-out_obj:
|+    visit_type_q_obj_BLOCK_JOB_ERROR_arg_members(v, &param, &err);
|     visit_end_struct(v, err ? NULL : &err);

Notice that the initialization of 'param' has to cast away const
(just as the old gen_visit_members() had to do): we can't change
the signature of the user function (which uses 'const char *'), but
have to assign it to a non-const QAPI object (which requires
'char *').

Likewise, command marshalling generates call arguments from a
stack-allocated struct, rather than a list of local variables:

|@@ -57,26 +57,15 @@ void qmp_marshal_add_fd(QDict *args, QOb
|     QmpInputVisitor *qiv = qmp_input_visitor_new_strict(QOBJECT(args));
|     QapiDeallocVisitor *qdv;
|     Visitor *v;
|-    bool has_fdset_id = false;
|-    int64_t fdset_id = 0;
|-    bool has_opaque = false;
|-    char *opaque = NULL;
|-
|-    v = qmp_input_get_visitor(qiv);
|-    if (visit_optional(v, "fdset-id", &has_fdset_id)) {
|-        visit_type_int(v, "fdset-id", &fdset_id, &err);
|-        if (err) {
|-            goto out;
|-        }
|-    }
|-    if (visit_optional(v, "opaque", &has_opaque)) {
|-        visit_type_str(v, "opaque", &opaque, &err);
|-        if (err) {
|-            goto out;
|-        }
|+    q_obj_add_fd_arg qapi = {0};
|+
|+    v = qmp_input_get_visitor(qiv);
|+    visit_type_q_obj_add_fd_arg_members(v, &qapi, &err);
|+    if (err) {
|+        goto out;
|     }
|
|-    retval = qmp_add_fd(has_fdset_id, fdset_id, has_opaque, opaque, &err);
|+    retval = qmp_add_fd(qapi.has_fdset_id, qapi.fdset_id, qapi.has_opaque, 
qapi.opaque, &err);
|     if (err) {
|         goto out;
|     }
|@@ -88,12 +77,7 @@ out:
|     qmp_input_visitor_cleanup(qiv);
|     qdv = qapi_dealloc_visitor_new();
|     v = qapi_dealloc_get_visitor(qdv);
|-    if (visit_optional(v, "fdset-id", &has_fdset_id)) {
|-        visit_type_int(v, "fdset-id", &fdset_id, NULL);
|-    }
|-    if (visit_optional(v, "opaque", &has_opaque)) {
|-        visit_type_str(v, "opaque", &opaque, NULL);
|-    }
|+    visit_type_q_obj_add_fd_arg_members(v, &qapi, NULL);
|     qapi_dealloc_visitor_cleanup(qdv);
| }

For the marshaller, it has the nice side effect of eliminating a
chance of collision between argument QMP names and local variables.

A similar collision still exists in the qapi_event_send_FOO().
Document it with a FIXME comment.

This patch also paves the way for some followup simplifications
in the generator, in subsequent patches.

Signed-off-by: Eric Blake <address@hidden>

Message-Id: <address@hidden>
---
 scripts/qapi-commands.py | 28 ++++++++++++----------------
 scripts/qapi-event.py    | 48 ++++++++++++++++++++++++++++++++++++++----------
 2 files changed, 50 insertions(+), 26 deletions(-)

diff --git a/scripts/qapi-commands.py b/scripts/qapi-commands.py
index 3784f33..5ffc381 100644
--- a/scripts/qapi-commands.py
+++ b/scripts/qapi-commands.py
@@ -33,8 +33,8 @@ def gen_call(name, arg_type, ret_type):
         assert not arg_type.variants
         for memb in arg_type.members:
             if memb.optional:
-                argstr += 'has_%s, ' % c_name(memb.name)
-            argstr += '%s, ' % c_name(memb.name)
+                argstr += 'qapi.has_%s, ' % c_name(memb.name)
+            argstr += 'qapi.%s, ' % c_name(memb.name)
 
     lhs = ''
     if ret_type:
@@ -71,21 +71,10 @@ def gen_marshal_vars(arg_type, ret_type):
     QmpInputVisitor *qiv = qmp_input_visitor_new_strict(QOBJECT(args));
     QapiDeallocVisitor *qdv;
     Visitor *v;
-''')
+    %(c_name)s qapi = {0};
 
-        for memb in arg_type.members:
-            if memb.optional:
-                ret += mcgen('''
-    bool has_%(c_name)s = false;
 ''',
-                             c_name=c_name(memb.name))
-            ret += mcgen('''
-    %(c_type)s %(c_name)s = %(c_null)s;
-''',
-                         c_name=c_name(memb.name),
-                         c_type=memb.type.c_type(),
-                         c_null=memb.type.c_null())
-        ret += '\n'
+                     c_name=arg_type.c_name())
     else:
         ret += mcgen('''
 
@@ -107,17 +96,24 @@ def gen_marshal_input_visit(arg_type, dealloc=False):
     qdv = qapi_dealloc_visitor_new();
     v = qapi_dealloc_get_visitor(qdv);
 ''')
+        errp = 'NULL'
     else:
         ret += mcgen('''
     v = qmp_input_get_visitor(qiv);
 ''')
+        errp = '&err'
 
-    ret += gen_visit_members(arg_type.members, skiperr=dealloc)
+    ret += mcgen('''
+    visit_type_%(c_name)s_members(v, &qapi, %(errp)s);
+''',
+                 c_name=arg_type.c_name(), errp=errp)
 
     if dealloc:
         ret += mcgen('''
     qapi_dealloc_visitor_cleanup(qdv);
 ''')
+    else:
+        ret += gen_err_check()
     return ret
 
 
diff --git a/scripts/qapi-event.py b/scripts/qapi-event.py
index 27af206..9b5c5b5 100644
--- a/scripts/qapi-event.py
+++ b/scripts/qapi-event.py
@@ -28,7 +28,37 @@ def gen_event_send_decl(name, arg_type):
                  proto=gen_event_send_proto(name, arg_type))
 
 
+# Declare and initialize an object 'qapi' using parameters from gen_params()
+def gen_param_var(typ):
+    assert not typ.variants
+    ret = mcgen('''
+    %(c_name)s param = {
+''',
+                c_name=typ.c_name())
+    sep = '        '
+    for memb in typ.members:
+        ret += sep
+        sep = ', '
+        if memb.optional:
+            ret += 'has_' + c_name(memb.name) + sep
+        if memb.type.name == 'str':
+            # Cast away const added in gen_params()
+            ret += '(char *)'
+        ret += c_name(memb.name)
+    ret += mcgen('''
+
+    };
+''')
+    return ret
+
+
 def gen_event_send(name, arg_type):
+    # FIXME: Our declaration of local variables (and of 'errp' in the
+    # parameter list) can collide with exploded members of the event's
+    # data type passed in as parameters.  If this collision ever hits in
+    # practice, we can rename our local variables with a leading _ prefix,
+    # or split the code into a wrapper function that creates a boxed
+    # 'param' object then calls another to do the real work.
     ret = mcgen('''
 
 %(proto)s
@@ -43,10 +73,11 @@ def gen_event_send(name, arg_type):
         ret += mcgen('''
     QmpOutputVisitor *qov;
     Visitor *v;
-
 ''')
+        ret += gen_param_var(arg_type)
 
     ret += mcgen('''
+
     emit = qmp_event_get_func_emit();
     if (!emit) {
         return;
@@ -58,26 +89,23 @@ def gen_event_send(name, arg_type):
                  name=name)
 
     if arg_type and arg_type.members:
-        assert not arg_type.variants
         ret += mcgen('''
     qov = qmp_output_visitor_new();
     v = qmp_output_get_visitor(qov);
 
     visit_start_struct(v, "%(name)s", NULL, 0, &err);
-''',
-                     name=name)
-        ret += gen_err_check()
-        ret += gen_visit_members(arg_type.members, need_cast=True,
-                                 label='out_obj')
-        ret += mcgen('''
-out_obj:
+    if (err) {
+        goto out;
+    }
+    visit_type_%(c_name)s_members(v, &param, &err);
     visit_end_struct(v, err ? NULL : &err);
     if (err) {
         goto out;
     }
 
     qdict_put_obj(qmp, "data", qmp_output_get_qobject(qov));
-''')
+''',
+                     name=name, c_name=arg_type.c_name())
 
     ret += mcgen('''
     emit(%(c_enum)s, qmp, &err);
-- 
2.4.3