[Qemu-devel] [PATCH v7 16/18] qapi: Share gen_visit_fields()

[Eric Blake]

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);

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

---
v7: massage the commit message, rebase on simpler gen_err_check()
v6: retitle 10/46, split gen_err_check() to its own patch,
improve commit message, use named parameters in gen_visit_fields()
to minimize effort of callers
---
 scripts/qapi-commands.py | 27 +--------------------------
 scripts/qapi-event.py    | 31 +------------------------------
 scripts/qapi-visit.py    | 22 +---------------------
 scripts/qapi.py          | 43 +++++++++++++++++++++++++++++++++++++++++++
 4 files changed, 46 insertions(+), 77 deletions(-)

diff --git a/scripts/qapi-commands.py b/scripts/qapi-commands.py
index 4e99c1d..9d214a6 100644
--- a/scripts/qapi-commands.py
+++ b/scripts/qapi-commands.py
@@ -101,7 +101,6 @@ def gen_marshal_input_visit(arg_type, dealloc=False):
         return ret

     if dealloc:
-        errparg = 'NULL'
         errarg = None
         ret += mcgen('''
     qmp_input_visitor_cleanup(qiv);
@@ -109,36 +108,12 @@ def gen_marshal_input_visit(arg_type, dealloc=False):
     v = qapi_dealloc_get_visitor(qdv);
 ''')
     else:
-        errparg = '&err'
         errarg = 'err'
         ret += mcgen('''
     v = qmp_input_get_visitor(qiv);
 ''')

-    for memb in arg_type.members:
-        if memb.optional:
-            ret += mcgen('''
-    visit_optional(v, &has_%(c_name)s, "%(name)s", %(errp)s);
-''',
-                         c_name=c_name(memb.name), name=memb.name,
-                         errp=errparg)
-            ret += gen_err_check(err=errarg)
-            ret += mcgen('''
-    if (has_%(c_name)s) {
-''',
-                         c_name=c_name(memb.name))
-            push_indent()
-        ret += mcgen('''
-    visit_type_%(c_type)s(v, &%(c_name)s, "%(name)s", %(errp)s);
-''',
-                     c_name=c_name(memb.name), name=memb.name,
-                     c_type=memb.type.c_name(), errp=errparg)
-        ret += gen_err_check(err=errarg)
-        if memb.optional:
-            pop_indent()
-            ret += mcgen('''
-    }
-''')
+    ret += gen_visit_fields(arg_type.members, errarg=errarg)

     if dealloc:
         ret += mcgen('''
diff --git a/scripts/qapi-event.py b/scripts/qapi-event.py
index b6951e6..b5e4d59 100644
--- a/scripts/qapi-event.py
+++ b/scripts/qapi-event.py
@@ -71,36 +71,7 @@ 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);
diff --git a/scripts/qapi-visit.py b/scripts/qapi-visit.py
index bc6911f..4f97781 100644
--- a/scripts/qapi-visit.py
+++ b/scripts/qapi-visit.py
@@ -85,27 +85,7 @@ 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/scripts/qapi.py b/scripts/qapi.py
index 62a415c..ada6380 100644
--- a/scripts/qapi.py
+++ b/scripts/qapi.py
@@ -1548,6 +1548,49 @@ 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
 #
-- 
2.4.3