qapi: Add a 'coroutine' flag for commands

This patch adds a new 'coroutine' flag to QMP command definitions that
tells the QMP dispatcher that the command handler is safe to be run in a
coroutine.

The documentation of the new flag pretends that this flag is already
used as intended, which it isn't yet after this patch. We'll implement
this in another patch in this series.

Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Message-Id: <20201005155855.256490-9-kwolf@redhat.com>
Reviewed-by: Markus Armbruster <armbru@redhat.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: Markus Armbruster <armbru@redhat.com>

4 files changed, 26 insertions, 10 deletions

diff --git a/scripts/qapi/commands.py b/scripts/qapi/commands.py
index 3cf9e1110b..6e6fc94a14 100644
--- a/scripts/qapi/commands.py
+++ b/scripts/qapi/commands.py
@@ -176,7 +176,8 @@ out:
     return ret
 
 
-def gen_register_command(name, success_response, allow_oob, allow_preconfig):
+def gen_register_command(name, success_response, allow_oob, allow_preconfig,
+                         coroutine):
     options = []
 
     if not success_response:
@@ -185,6 +186,8 @@ def gen_register_command(name, success_response, allow_oob, allow_preconfig):
         options += ['QCO_ALLOW_OOB']
     if allow_preconfig:
         options += ['QCO_ALLOW_PRECONFIG']
+    if coroutine:
+        options += ['QCO_COROUTINE']
 
     if not options:
         options = ['QCO_NO_OPTIONS']
@@ -267,7 +270,7 @@ void %(c_prefix)sqmp_init_marshal(QmpCommandList *cmds);
 
     def visit_command(self, name, info, ifcond, features,
                       arg_type, ret_type, gen, success_response, boxed,
-                      allow_oob, allow_preconfig):
+                      allow_oob, allow_preconfig, coroutine):
         if not gen:
             return
         # FIXME: If T is a user-defined type, the user is responsible
@@ -285,7 +288,8 @@ void %(c_prefix)sqmp_init_marshal(QmpCommandList *cmds);
             self._genh.add(gen_marshal_decl(name))
             self._genc.add(gen_marshal(name, arg_type, boxed, ret_type))
             self._regy.add(gen_register_command(name, success_response,
-                                                allow_oob, allow_preconfig))
+                                                allow_oob, allow_preconfig,
+                                                coroutine))
 
 
 def gen_commands(schema, output_dir, prefix):
diff --git a/scripts/qapi/expr.py b/scripts/qapi/expr.py
index 2942520399..a15c1fb474 100644
--- a/scripts/qapi/expr.py
+++ b/scripts/qapi/expr.py
@@ -88,10 +88,17 @@ def check_flags(expr, info):
         if key in expr and expr[key] is not False:
             raise QAPISemError(
                 info, "flag '%s' may only use false value" % key)
-    for key in ['boxed', 'allow-oob', 'allow-preconfig']:
+    for key in ['boxed', 'allow-oob', 'allow-preconfig', 'coroutine']:
         if key in expr and expr[key] is not True:
             raise QAPISemError(
                 info, "flag '%s' may only use true value" % key)
+    if 'allow-oob' in expr and 'coroutine' in expr:
+        # This is not necessarily a fundamental incompatibility, but
+        # we don't have a use case and the desired semantics isn't
+        # obvious.  The simplest solution is to forbid it until we get
+        # a use case for it.
+        raise QAPISemError(info, "flags 'allow-oob' and 'coroutine' "
+                                 "are incompatible")
 
 
 def check_if(expr, info, source):
@@ -342,7 +349,7 @@ def check_exprs(exprs):
                        ['command'],
                        ['data', 'returns', 'boxed', 'if', 'features',
                         'gen', 'success-response', 'allow-oob',
-                        'allow-preconfig'])
+                        'allow-preconfig', 'coroutine'])
             normalize_members(expr.get('data'))
             check_command(expr, info)
         elif meta == 'event':
diff --git a/scripts/qapi/introspect.py b/scripts/qapi/introspect.py
index 23652be810..5907b09cd5 100644
--- a/scripts/qapi/introspect.py
+++ b/scripts/qapi/introspect.py
@@ -216,7 +216,7 @@ const QLitObject %(c_name)s = %(c_string)s;
 
     def visit_command(self, name, info, ifcond, features,
                       arg_type, ret_type, gen, success_response, boxed,
-                      allow_oob, allow_preconfig):
+                      allow_oob, allow_preconfig, coroutine):
         arg_type = arg_type or self._schema.the_empty_object_type
         ret_type = ret_type or self._schema.the_empty_object_type
         obj = {'arg-type': self._use_type(arg_type),
diff --git a/scripts/qapi/schema.py b/scripts/qapi/schema.py
index 78309a00f0..d1307ec661 100644
--- a/scripts/qapi/schema.py
+++ b/scripts/qapi/schema.py
@@ -128,7 +128,7 @@ class QAPISchemaVisitor:
 
     def visit_command(self, name, info, ifcond, features,
                       arg_type, ret_type, gen, success_response, boxed,
-                      allow_oob, allow_preconfig):
+                      allow_oob, allow_preconfig, coroutine):
         pass
 
     def visit_event(self, name, info, ifcond, features, arg_type, boxed):
@@ -713,7 +713,8 @@ class QAPISchemaCommand(QAPISchemaEntity):
 
     def __init__(self, name, info, doc, ifcond, features,
                  arg_type, ret_type,
-                 gen, success_response, boxed, allow_oob, allow_preconfig):
+                 gen, success_response, boxed, allow_oob, allow_preconfig,
+                 coroutine):
         super().__init__(name, info, doc, ifcond, features)
         assert not arg_type or isinstance(arg_type, str)
         assert not ret_type or isinstance(ret_type, str)
@@ -726,6 +727,7 @@ class QAPISchemaCommand(QAPISchemaEntity):
         self.boxed = boxed
         self.allow_oob = allow_oob
         self.allow_preconfig = allow_preconfig
+        self.coroutine = coroutine
 
     def check(self, schema):
         super().check(schema)
@@ -768,7 +770,8 @@ class QAPISchemaCommand(QAPISchemaEntity):
         visitor.visit_command(
             self.name, self.info, self.ifcond, self.features,
             self.arg_type, self.ret_type, self.gen, self.success_response,
-            self.boxed, self.allow_oob, self.allow_preconfig)
+            self.boxed, self.allow_oob, self.allow_preconfig,
+            self.coroutine)
 
 
 class QAPISchemaEvent(QAPISchemaEntity):
@@ -1074,6 +1077,7 @@ class QAPISchema:
         boxed = expr.get('boxed', False)
         allow_oob = expr.get('allow-oob', False)
         allow_preconfig = expr.get('allow-preconfig', False)
+        coroutine = expr.get('coroutine', False)
         ifcond = expr.get('if')
         features = self._make_features(expr.get('features'), info)
         if isinstance(data, OrderedDict):
@@ -1086,7 +1090,8 @@ class QAPISchema:
         self._def_entity(QAPISchemaCommand(name, info, doc, ifcond, features,
                                            data, rets,
                                            gen, success_response,
-                                           boxed, allow_oob, allow_preconfig))
+                                           boxed, allow_oob, allow_preconfig,
+                                           coroutine))
 
     def _def_event(self, expr, info, doc):
         name = expr['event']