@@ -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']
@@ -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)
@@ -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
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> --- docs/devel/qapi-code-gen.txt | 29 +++++++++++++++++++++++++ docs/sphinx/qapidoc.py | 2 +- include/qapi/qmp/dispatch.h | 1 + tests/test-qmp-cmds.c | 4 ++++ scripts/qapi/commands.py | 10 ++++++--- scripts/qapi/expr.py | 11 ++++++++-- scripts/qapi/introspect.py | 2 +- scripts/qapi/schema.py | 13 +++++++---- tests/qapi-schema/test-qapi.py | 7 +++--- tests/qapi-schema/meson.build | 1 + tests/qapi-schema/oob-coroutine.err | 2 ++ tests/qapi-schema/oob-coroutine.json | 2 ++ tests/qapi-schema/oob-coroutine.out | 0 tests/qapi-schema/qapi-schema-test.json | 1 + tests/qapi-schema/qapi-schema-test.out | 2 ++ 15 files changed, 73 insertions(+), 14 deletions(-) create mode 100644 tests/qapi-schema/oob-coroutine.err create mode 100644 tests/qapi-schema/oob-coroutine.json create mode 100644 tests/qapi-schema/oob-coroutine.out