@@ -472,6 +472,7 @@ Syntax:
'*gen': false,
'*allow-oob': true,
'*allow-preconfig': true,
+ '*coroutine': true,
'*if': COND,
'*features': FEATURES }
@@ -596,6 +597,34 @@ before the machine is built. It defaults to false. For example:
QMP is available before the machine is built only when QEMU was
started with --preconfig.
+Member 'coroutine' tells the QMP dispatcher whether the command handler
+is safe to be run in a coroutine. It defaults to false. If it is true,
+the command handler is called from coroutine context and may yield while
+waiting for an external event (such as I/O completion) in order to avoid
+blocking the guest and other background operations.
+
+Coroutine safety can be hard to prove, similar to thread safety. Common
+pitfalls are:
+
+- The global mutex isn't held across qemu_coroutine_yield(), so
+ operations that used to assume that they execute atomically may have
+ to be more careful to protect against changes in the global state.
+
+- Nested event loops (AIO_WAIT_WHILE() etc.) are problematic in
+ coroutine context and can easily lead to deadlocks. They should be
+ replaced by yielding and reentering the coroutine when the condition
+ becomes false.
+
+Since the command handler may assume coroutine context, any callers
+other than the QMP dispatcher must also call it in coroutine context.
+In particular, HMP commands calling such a QMP command handler must
+enter coroutine context before calling the handler.
+
+It is an error to specify both 'coroutine': true and 'allow-oob': true
+for a command. We don't currently have a use case for both together and
+without a use case, it's not entirely clear what the semantics should
+be.
+
The optional 'if' member specifies a conditional. See "Configuring
the schema" below for more on this.
@@ -330,7 +330,7 @@ class QAPISchemaGenRSTVisitor(QAPISchemaVisitor):
def visit_command(self, name, info, ifcond, features, arg_type,
ret_type, gen, success_response, boxed, allow_oob,
- allow_preconfig):
+ allow_preconfig, coroutine):
doc = self._cur_doc
self._add_doc('Command',
self._nodes_for_arguments(doc,
@@ -25,6 +25,7 @@ typedef enum QmpCommandOptions
QCO_NO_SUCCESS_RESP = (1U << 0),
QCO_ALLOW_OOB = (1U << 1),
QCO_ALLOW_PRECONFIG = (1U << 2),
+ QCO_COROUTINE = (1U << 3),
} QmpCommandOptions;
typedef struct QmpCommand
@@ -36,6 +36,10 @@ void qmp_cmd_success_response(Error **errp)
{
}
+void qmp_coroutine_cmd(Error **errp)
+{
+}
+
Empty2 *qmp_user_def_cmd0(Error **errp)
{
return g_new0(Empty2, 1);
@@ -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):
@@ -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':
@@ -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),
@@ -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']
@@ -142,6 +142,7 @@ schemas = [
'nested-struct-data.json',
'nested-struct-data-invalid-dict.json',
'non-objects.json',
+ 'oob-coroutine.json',
'oob-test.json',
'allow-preconfig-test.json',
'pragma-doc-required-crap.json',
new file mode 100644
@@ -0,0 +1,2 @@
+oob-coroutine.json: In command 'oob-command-1':
+oob-coroutine.json:2: flags 'allow-oob' and 'coroutine' are incompatible
new file mode 100644
@@ -0,0 +1,2 @@
+# Check that incompatible flags allow-oob and coroutine are rejected
+{ 'command': 'oob-command-1', 'allow-oob': true, 'coroutine': true }
new file mode 100644
@@ -148,6 +148,7 @@
'returns': 'UserDefTwo' }
{ 'command': 'cmd-success-response', 'data': {}, 'success-response': false }
+{ 'command': 'coroutine-cmd', 'data': {}, 'coroutine': true }
# Returning a non-dictionary requires a name from the whitelist
{ 'command': 'guest-get-time', 'data': {'a': 'int', '*b': 'int' },
@@ -203,6 +203,8 @@ command user_def_cmd2 q_obj_user_def_cmd2-arg -> UserDefTwo
gen=True success_response=True boxed=False oob=False preconfig=False
command cmd-success-response None -> None
gen=True success_response=False boxed=False oob=False preconfig=False
+command coroutine-cmd None -> None
+ gen=True success_response=True boxed=False oob=False preconfig=False coroutine=True
object q_obj_guest-get-time-arg
member a: int optional=False
member b: int optional=True
@@ -68,12 +68,13 @@ class QAPISchemaTestVisitor(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):
print('command %s %s -> %s'
% (name, arg_type and arg_type.name,
ret_type and ret_type.name))
- print(' gen=%s success_response=%s boxed=%s oob=%s preconfig=%s'
- % (gen, success_response, boxed, allow_oob, allow_preconfig))
+ print(' gen=%s success_response=%s boxed=%s oob=%s preconfig=%s%s'
+ % (gen, success_response, boxed, allow_oob, allow_preconfig,
+ " coroutine=True" if coroutine else ""))
self._print_if(ifcond)
self._print_features(features)