qapi: add const prefix to 'char *' insider c_type()

It's ugly to add const prefix for parameter type by an if statement
outside c_type(). This patch adds a parameter to do it.

Signed-off-by: Amos Kong <akong@redhat.com>
Suggested-by: Markus Armbruster <armbru@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>
Reviewed-by: Markus Armbruster <armbru@redhat.com>
Signed-off-by: Luiz Capitulino <lcapitulino@redhat.com>

scripts/qapi-commands.py

@@ -29,9 +29,7 @@ def type_visitor(name):
 def generate_command_decl(name, args, ret_type):
     arglist=""
     for argname, argtype, optional, structured in parse_args(args):
-        argtype = c_type(argtype)
-        if argtype == "char *":
-            argtype = "const char *"
+        argtype = c_type(argtype, is_param=True)
         if optional:
             arglist += "bool has_%s, " % c_var(argname)
         arglist += "%s %s, " % (argtype, c_var(argname))

scripts/qapi.py

@@ -470,8 +470,10 @@ def find_enum(name):
 def is_enum(name):
     return find_enum(name) != None
 
-def c_type(name):
+def c_type(name, is_param=False):
     if name == 'str':
+        if is_param:
+            return 'const char *'
         return 'char *'
     elif name == 'int':
         return 'int64_t'