From 4ca10929a74404968b4933d1e11415cad4fd313c Mon Sep 17 00:00:00 2001
From: Eric Blake <eblake@redhat.com>
Date: Mon, 19 Feb 2018 18:41:37 -0500
Subject: [PATCH] qapi: Share gen_visit_fields()

Consolidate the code between visit, command marshalling, and
event generation that iterates over the members of a struct.
It reduces code duplication in the generator, so that a future
patch can reduce the size of generated code while touching only
one instead of three locations.

There are no changes to the generated marshal code.

The visitor code becomes slightly more verbose, but remains
semantically equivalent, and is actually easier to read as
it follows a more common idiom:

| visit_optional(v, &(*obj)->has_device, "device", &err);
|- if (!err && (*obj)->has_device) {
|- visit_type_str(v, &(*obj)->device, "device", &err);
|- }
| if (err) {
| goto out;
| }
|+ if ((*obj)->has_device) {
|+ visit_type_str(v, &(*obj)->device, "device", &err);
|+ if (err) {
|+ goto out;
|+ }
|+ }

The event code becomes slightly more verbose, but this is
arguably a bug fix: although the visitors are not well
documented, use of an optional member should not be attempted
unless guarded by a prior call to visit_optional(). Works only
because the output qmp visitor has a no-op visit_optional():

|+ visit_optional(v, &has_offset, "offset", &err);
|+ if (err) {
|+ goto out;
|+ }
| if (has_offset) {
| visit_type_int(v, &offset, "offset", &err);

Backports commit 82ca8e469666b169ccf818a0e36136aee97d7db0 from qemu
---
 qemu/scripts/qapi-event.py | 31 +---------------------------
 qemu/scripts/qapi-visit.py | 22 +-------------------
 qemu/scripts/qapi.py       | 42 ++++++++++++++++++++++++++++++++++++++
 3 files changed, 44 insertions(+), 51 deletions(-)

diff --git a/qemu/scripts/qapi-event.py b/qemu/scripts/qapi-event.py
index aa516ef1..1d154694 100644
--- a/qemu/scripts/qapi-event.py
+++ b/qemu/scripts/qapi-event.py
@@ -70,36 +70,7 @@ def gen_event_send(name, arg_type):
 ''',
                      name=name)
         ret += gen_err_check()
-
-        for memb in arg_type.members:
-            if memb.optional:
-                ret += mcgen('''
-    if (has_%(c_name)s) {
-''',
-                             c_name=c_name(memb.name))
-                push_indent()
-
-            # Ugly: need to cast away the const
-            if memb.type.name == "str":
-                cast = '(char **)'
-            else:
-                cast = ''
-
-            ret += mcgen('''
-    visit_type_%(c_type)s(v, %(cast)s&%(c_name)s, "%(name)s", &err);
-''',
-                         cast=cast,
-                         c_name=c_name(memb.name),
-                         c_type=memb.type.c_name(),
-                         name=memb.name)
-            ret += gen_err_check()
-
-            if memb.optional:
-                pop_indent()
-                ret += mcgen('''
-    }
-''')
-
+        ret += gen_visit_fields(arg_type.members, need_cast=True)
         ret += mcgen('''
     visit_end_struct(v, &err);
     if (err) {
diff --git a/qemu/scripts/qapi-visit.py b/qemu/scripts/qapi-visit.py
index fe35d8f9..e709791f 100644
--- a/qemu/scripts/qapi-visit.py
+++ b/qemu/scripts/qapi-visit.py
@@ -83,27 +83,7 @@ static void visit_type_%(c_name)s_fields(Visitor *v, %(c_name)s **obj, Error **e
                      c_type=base.c_name(), c_name=c_name('base'))
         ret += gen_err_check()
 
-    for memb in members:
-        if memb.optional:
-            ret += mcgen('''
-    visit_optional(v, &(*obj)->has_%(c_name)s, "%(name)s", &err);
-    if (!err && (*obj)->has_%(c_name)s) {
-''',
-                         c_name=c_name(memb.name), name=memb.name)
-            push_indent()
-
-        ret += mcgen('''
-    visit_type_%(c_type)s(v, &(*obj)->%(c_name)s, "%(name)s", &err);
-''',
-                     c_type=memb.type.c_name(), c_name=c_name(memb.name),
-                     name=memb.name)
-
-        if memb.optional:
-            pop_indent()
-            ret += mcgen('''
-    }
-''')
-        ret += gen_err_check()
+    ret += gen_visit_fields(members, prefix='(*obj)->')
 
     if re.search('^ *goto out;', ret, re.MULTILINE):
         ret += mcgen('''
diff --git a/qemu/scripts/qapi.py b/qemu/scripts/qapi.py
index 96287056..51c54549 100644
--- a/qemu/scripts/qapi.py
+++ b/qemu/scripts/qapi.py
@@ -1543,6 +1543,48 @@ def gen_err_check(err='err', label='out'):
                  err=err, label=label)
 
 
+def gen_visit_fields(members, prefix='', need_cast=False, errarg='err'):
+    ret = ''
+    if errarg:
+        errparg = '&' + errarg
+    else:
+        errparg = 'NULL'
+
+    for memb in members:
+        if memb.optional:
+            ret += mcgen('''
+    visit_optional(v, &%(prefix)shas_%(c_name)s, "%(name)s", %(errp)s);
+''',
+                         prefix=prefix, c_name=c_name(memb.name),
+                         name=memb.name, errp=errparg)
+            ret += gen_err_check(err=errarg)
+            ret += mcgen('''
+    if (%(prefix)shas_%(c_name)s) {
+''',
+                         prefix=prefix, c_name=c_name(memb.name))
+            push_indent()
+
+        # Ugly: sometimes we need to cast away const
+        if need_cast and memb.type.name == 'str':
+            cast = '(char **)'
+        else:
+            cast = ''
+
+        ret += mcgen('''
+    visit_type_%(c_type)s(v, %(cast)s&%(prefix)s%(c_name)s, "%(name)s", %(errp)s);
+''',
+                     c_type=memb.type.c_name(), prefix=prefix, cast=cast,
+                     c_name=c_name(memb.name), name=memb.name,
+                     errp=errparg)
+        ret += gen_err_check(err=errarg)
+
+        if memb.optional:
+            pop_indent()
+            ret += mcgen('''
+    }
+''')
+    return ret
+
 #
 # Common command line parsing
 #