qemu/monitor/qmp.c
Wolfgang Bumiller 2895aaa139 monitor/qmp: resume monitor when clearing its queue
When a monitor's queue is filled up in handle_qmp_command()
it gets suspended. It's the dispatcher bh's job currently to
resume the monitor, which it does after processing an event
from the queue. However, it is possible for a
CHR_EVENT_CLOSED event to be processed before before the bh
is scheduled, which will clear the queue without resuming
the monitor, thereby preventing the dispatcher from reaching
the resume() call.
Any new connections to the qmp socket will be accept()ed and
show the greeting, but will not respond to any messages sent
afterwards (as they will not be read from the
still-suspended socket).
Fix this by resuming the monitor when clearing a queue which
was filled up.

Signed-off-by: Wolfgang Bumiller <w.bumiller@proxmox.com>
Message-Id: <20191115085914.21287-1-w.bumiller@proxmox.com>
2019-11-19 08:21:47 +01:00

431 lines
13 KiB
C

/*
* QEMU monitor
*
* Copyright (c) 2003-2004 Fabrice Bellard
*
* Permission is hereby granted, free of charge, to any person obtaining a copy
* of this software and associated documentation files (the "Software"), to deal
* in the Software without restriction, including without limitation the rights
* to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
* copies of the Software, and to permit persons to whom the Software is
* furnished to do so, subject to the following conditions:
*
* The above copyright notice and this permission notice shall be included in
* all copies or substantial portions of the Software.
*
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
* THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
* OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
* THE SOFTWARE.
*/
#include "qemu/osdep.h"
#include "chardev/char-io.h"
#include "monitor-internal.h"
#include "qapi/error.h"
#include "qapi/qapi-commands-misc.h"
#include "qapi/qmp/qdict.h"
#include "qapi/qmp/qjson.h"
#include "qapi/qmp/qlist.h"
#include "qapi/qmp/qstring.h"
#include "trace.h"
struct QMPRequest {
/* Owner of the request */
MonitorQMP *mon;
/*
* Request object to be handled or Error to be reported
* (exactly one of them is non-null)
*/
QObject *req;
Error *err;
};
typedef struct QMPRequest QMPRequest;
QmpCommandList qmp_commands, qmp_cap_negotiation_commands;
static bool qmp_oob_enabled(MonitorQMP *mon)
{
return mon->capab[QMP_CAPABILITY_OOB];
}
static void monitor_qmp_caps_reset(MonitorQMP *mon)
{
memset(mon->capab_offered, 0, sizeof(mon->capab_offered));
memset(mon->capab, 0, sizeof(mon->capab));
mon->capab_offered[QMP_CAPABILITY_OOB] = mon->common.use_io_thread;
}
static void qmp_request_free(QMPRequest *req)
{
qobject_unref(req->req);
error_free(req->err);
g_free(req);
}
/* Caller must hold mon->qmp.qmp_queue_lock */
static void monitor_qmp_cleanup_req_queue_locked(MonitorQMP *mon)
{
while (!g_queue_is_empty(mon->qmp_requests)) {
qmp_request_free(g_queue_pop_head(mon->qmp_requests));
}
}
static void monitor_qmp_cleanup_queue_and_resume(MonitorQMP *mon)
{
qemu_mutex_lock(&mon->qmp_queue_lock);
/*
* Same condition as in monitor_qmp_bh_dispatcher(), but before
* removing an element from the queue (hence no `- 1`).
* Also, the queue should not be empty either, otherwise the
* monitor hasn't been suspended yet (or was already resumed).
*/
bool need_resume = (!qmp_oob_enabled(mon) ||
mon->qmp_requests->length == QMP_REQ_QUEUE_LEN_MAX)
&& !g_queue_is_empty(mon->qmp_requests);
monitor_qmp_cleanup_req_queue_locked(mon);
if (need_resume) {
/*
* handle_qmp_command() suspended the monitor because the
* request queue filled up, to be resumed when the queue has
* space again. We just emptied it; resume the monitor.
*
* Without this, the monitor would remain suspended forever
* when we get here while the monitor is suspended. An
* unfortunately timed CHR_EVENT_CLOSED can do the trick.
*/
monitor_resume(&mon->common);
}
qemu_mutex_unlock(&mon->qmp_queue_lock);
}
void qmp_send_response(MonitorQMP *mon, const QDict *rsp)
{
const QObject *data = QOBJECT(rsp);
QString *json;
json = mon->pretty ? qobject_to_json_pretty(data) : qobject_to_json(data);
assert(json != NULL);
qstring_append_chr(json, '\n');
monitor_puts(&mon->common, qstring_get_str(json));
qobject_unref(json);
}
/*
* Emit QMP response @rsp to @mon.
* Null @rsp can only happen for commands with QCO_NO_SUCCESS_RESP.
* Nothing is emitted then.
*/
static void monitor_qmp_respond(MonitorQMP *mon, QDict *rsp)
{
if (rsp) {
qmp_send_response(mon, rsp);
}
}
static void monitor_qmp_dispatch(MonitorQMP *mon, QObject *req)
{
Monitor *old_mon;
QDict *rsp;
QDict *error;
old_mon = cur_mon;
cur_mon = &mon->common;
rsp = qmp_dispatch(mon->commands, req, qmp_oob_enabled(mon));
cur_mon = old_mon;
if (mon->commands == &qmp_cap_negotiation_commands) {
error = qdict_get_qdict(rsp, "error");
if (error
&& !g_strcmp0(qdict_get_try_str(error, "class"),
QapiErrorClass_str(ERROR_CLASS_COMMAND_NOT_FOUND))) {
/* Provide a more useful error message */
qdict_del(error, "desc");
qdict_put_str(error, "desc", "Expecting capabilities negotiation"
" with 'qmp_capabilities'");
}
}
monitor_qmp_respond(mon, rsp);
qobject_unref(rsp);
}
/*
* Pop a QMP request from a monitor request queue.
* Return the request, or NULL all request queues are empty.
* We are using round-robin fashion to pop the request, to avoid
* processing commands only on a very busy monitor. To achieve that,
* when we process one request on a specific monitor, we put that
* monitor to the end of mon_list queue.
*
* Note: if the function returned with non-NULL, then the caller will
* be with qmp_mon->qmp_queue_lock held, and the caller is responsible
* to release it.
*/
static QMPRequest *monitor_qmp_requests_pop_any_with_lock(void)
{
QMPRequest *req_obj = NULL;
Monitor *mon;
MonitorQMP *qmp_mon;
qemu_mutex_lock(&monitor_lock);
QTAILQ_FOREACH(mon, &mon_list, entry) {
if (!monitor_is_qmp(mon)) {
continue;
}
qmp_mon = container_of(mon, MonitorQMP, common);
qemu_mutex_lock(&qmp_mon->qmp_queue_lock);
req_obj = g_queue_pop_head(qmp_mon->qmp_requests);
if (req_obj) {
/* With the lock of corresponding queue held */
break;
}
qemu_mutex_unlock(&qmp_mon->qmp_queue_lock);
}
if (req_obj) {
/*
* We found one request on the monitor. Degrade this monitor's
* priority to lowest by re-inserting it to end of queue.
*/
QTAILQ_REMOVE(&mon_list, mon, entry);
QTAILQ_INSERT_TAIL(&mon_list, mon, entry);
}
qemu_mutex_unlock(&monitor_lock);
return req_obj;
}
void monitor_qmp_bh_dispatcher(void *data)
{
QMPRequest *req_obj = monitor_qmp_requests_pop_any_with_lock();
QDict *rsp;
bool need_resume;
MonitorQMP *mon;
if (!req_obj) {
return;
}
mon = req_obj->mon;
/* qmp_oob_enabled() might change after "qmp_capabilities" */
need_resume = !qmp_oob_enabled(mon) ||
mon->qmp_requests->length == QMP_REQ_QUEUE_LEN_MAX - 1;
qemu_mutex_unlock(&mon->qmp_queue_lock);
if (req_obj->req) {
QDict *qdict = qobject_to(QDict, req_obj->req);
QObject *id = qdict ? qdict_get(qdict, "id") : NULL;
trace_monitor_qmp_cmd_in_band(qobject_get_try_str(id) ?: "");
monitor_qmp_dispatch(mon, req_obj->req);
} else {
assert(req_obj->err);
rsp = qmp_error_response(req_obj->err);
req_obj->err = NULL;
monitor_qmp_respond(mon, rsp);
qobject_unref(rsp);
}
if (need_resume) {
/* Pairs with the monitor_suspend() in handle_qmp_command() */
monitor_resume(&mon->common);
}
qmp_request_free(req_obj);
/* Reschedule instead of looping so the main loop stays responsive */
qemu_bh_schedule(qmp_dispatcher_bh);
}
static void handle_qmp_command(void *opaque, QObject *req, Error *err)
{
MonitorQMP *mon = opaque;
QObject *id = NULL;
QDict *qdict;
QMPRequest *req_obj;
assert(!req != !err);
qdict = qobject_to(QDict, req);
if (qdict) {
id = qdict_get(qdict, "id");
} /* else will fail qmp_dispatch() */
if (req && trace_event_get_state_backends(TRACE_HANDLE_QMP_COMMAND)) {
QString *req_json = qobject_to_json(req);
trace_handle_qmp_command(mon, qstring_get_str(req_json));
qobject_unref(req_json);
}
if (qdict && qmp_is_oob(qdict)) {
/* OOB commands are executed immediately */
trace_monitor_qmp_cmd_out_of_band(qobject_get_try_str(id) ?: "");
monitor_qmp_dispatch(mon, req);
qobject_unref(req);
return;
}
req_obj = g_new0(QMPRequest, 1);
req_obj->mon = mon;
req_obj->req = req;
req_obj->err = err;
/* Protect qmp_requests and fetching its length. */
qemu_mutex_lock(&mon->qmp_queue_lock);
/*
* Suspend the monitor when we can't queue more requests after
* this one. Dequeuing in monitor_qmp_bh_dispatcher() or
* monitor_qmp_cleanup_queue_and_resume() will resume it.
* Note that when OOB is disabled, we queue at most one command,
* for backward compatibility.
*/
if (!qmp_oob_enabled(mon) ||
mon->qmp_requests->length == QMP_REQ_QUEUE_LEN_MAX - 1) {
monitor_suspend(&mon->common);
}
/*
* Put the request to the end of queue so that requests will be
* handled in time order. Ownership for req_obj, req,
* etc. will be delivered to the handler side.
*/
assert(mon->qmp_requests->length < QMP_REQ_QUEUE_LEN_MAX);
g_queue_push_tail(mon->qmp_requests, req_obj);
qemu_mutex_unlock(&mon->qmp_queue_lock);
/* Kick the dispatcher routine */
qemu_bh_schedule(qmp_dispatcher_bh);
}
static void monitor_qmp_read(void *opaque, const uint8_t *buf, int size)
{
MonitorQMP *mon = opaque;
json_message_parser_feed(&mon->parser, (const char *) buf, size);
}
static QDict *qmp_greeting(MonitorQMP *mon)
{
QList *cap_list = qlist_new();
QObject *ver = NULL;
QMPCapability cap;
qmp_marshal_query_version(NULL, &ver, NULL);
for (cap = 0; cap < QMP_CAPABILITY__MAX; cap++) {
if (mon->capab_offered[cap]) {
qlist_append_str(cap_list, QMPCapability_str(cap));
}
}
return qdict_from_jsonf_nofail(
"{'QMP': {'version': %p, 'capabilities': %p}}",
ver, cap_list);
}
static void monitor_qmp_event(void *opaque, int event)
{
QDict *data;
MonitorQMP *mon = opaque;
switch (event) {
case CHR_EVENT_OPENED:
mon->commands = &qmp_cap_negotiation_commands;
monitor_qmp_caps_reset(mon);
data = qmp_greeting(mon);
qmp_send_response(mon, data);
qobject_unref(data);
mon_refcount++;
break;
case CHR_EVENT_CLOSED:
/*
* Note: this is only useful when the output of the chardev
* backend is still open. For example, when the backend is
* stdio, it's possible that stdout is still open when stdin
* is closed.
*/
monitor_qmp_cleanup_queue_and_resume(mon);
json_message_parser_destroy(&mon->parser);
json_message_parser_init(&mon->parser, handle_qmp_command,
mon, NULL);
mon_refcount--;
monitor_fdsets_cleanup();
break;
}
}
void monitor_data_destroy_qmp(MonitorQMP *mon)
{
json_message_parser_destroy(&mon->parser);
qemu_mutex_destroy(&mon->qmp_queue_lock);
monitor_qmp_cleanup_req_queue_locked(mon);
g_queue_free(mon->qmp_requests);
}
static void monitor_qmp_setup_handlers_bh(void *opaque)
{
MonitorQMP *mon = opaque;
GMainContext *context;
assert(mon->common.use_io_thread);
context = iothread_get_g_main_context(mon_iothread);
assert(context);
qemu_chr_fe_set_handlers(&mon->common.chr, monitor_can_read,
monitor_qmp_read, monitor_qmp_event,
NULL, &mon->common, context, true);
monitor_list_append(&mon->common);
}
void monitor_init_qmp(Chardev *chr, bool pretty)
{
MonitorQMP *mon = g_new0(MonitorQMP, 1);
/* Note: we run QMP monitor in I/O thread when @chr supports that */
monitor_data_init(&mon->common, true, false,
qemu_chr_has_feature(chr, QEMU_CHAR_FEATURE_GCONTEXT));
mon->pretty = pretty;
qemu_mutex_init(&mon->qmp_queue_lock);
mon->qmp_requests = g_queue_new();
qemu_chr_fe_init(&mon->common.chr, chr, &error_abort);
qemu_chr_fe_set_echo(&mon->common.chr, true);
json_message_parser_init(&mon->parser, handle_qmp_command, mon, NULL);
if (mon->common.use_io_thread) {
/*
* Make sure the old iowatch is gone. It's possible when
* e.g. the chardev is in client mode, with wait=on.
*/
remove_fd_in_watch(chr);
/*
* We can't call qemu_chr_fe_set_handlers() directly here
* since chardev might be running in the monitor I/O
* thread. Schedule a bottom half.
*/
aio_bh_schedule_oneshot(iothread_get_aio_context(mon_iothread),
monitor_qmp_setup_handlers_bh, mon);
/* The bottom half will add @mon to @mon_list */
} else {
qemu_chr_fe_set_handlers(&mon->common.chr, monitor_can_read,
monitor_qmp_read, monitor_qmp_event,
NULL, &mon->common, NULL, true);
monitor_list_append(&mon->common);
}
}