Introduce Virtio-loopback epsilon release:

Epsilon release introduces a new compatibility layer which make virtio-loopback
design to work with QEMU and rust-vmm vhost-user backend without require any
changes.

Signed-off-by: Timos Ampelikiotis <t.ampelikiotis@virtualopensystems.com>
Change-Id: I52e57563e08a7d0bdc002f8e928ee61ba0c53dd9

1 files changed, 778 insertions, 0 deletions

diff --git a/monitor/monitor.c b/monitor/monitor.c
new file mode 100644
index 000000000..21c7a6875
--- /dev/null
+++ b/monitor/monitor.c
@@ -0,0 +1,778 @@
+/*
+ * 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 "monitor-internal.h"
+#include "qapi/error.h"
+#include "qapi/opts-visitor.h"
+#include "qapi/qapi-emit-events.h"
+#include "qapi/qapi-visit-control.h"
+#include "qapi/qmp/qdict.h"
+#include "qemu/error-report.h"
+#include "qemu/option.h"
+#include "sysemu/qtest.h"
+#include "trace.h"
+
+/*
+ * To prevent flooding clients, events can be throttled. The
+ * throttling is calculated globally, rather than per-Monitor
+ * instance.
+ */
+typedef struct MonitorQAPIEventState {
+    QAPIEvent event;    /* Throttling state for this event type and... */
+    QDict *data;        /* ... data, see qapi_event_throttle_equal() */
+    QEMUTimer *timer;   /* Timer for handling delayed events */
+    QDict *qdict;       /* Delayed event (if any) */
+} MonitorQAPIEventState;
+
+typedef struct {
+    int64_t rate;       /* Minimum time (in ns) between two events */
+} MonitorQAPIEventConf;
+
+/* Shared monitor I/O thread */
+IOThread *mon_iothread;
+
+/* Coroutine to dispatch the requests received from I/O thread */
+Coroutine *qmp_dispatcher_co;
+
+/* Set to true when the dispatcher coroutine should terminate */
+bool qmp_dispatcher_co_shutdown;
+
+/*
+ * qmp_dispatcher_co_busy is used for synchronisation between the
+ * monitor thread and the main thread to ensure that the dispatcher
+ * coroutine never gets scheduled a second time when it's already
+ * scheduled (scheduling the same coroutine twice is forbidden).
+ *
+ * It is true if the coroutine is active and processing requests.
+ * Additional requests may then be pushed onto mon->qmp_requests,
+ * and @qmp_dispatcher_co_shutdown may be set without further ado.
+ * @qmp_dispatcher_co_busy must not be woken up in this case.
+ *
+ * If false, you also have to set @qmp_dispatcher_co_busy to true and
+ * wake up @qmp_dispatcher_co after pushing the new requests.
+ *
+ * The coroutine will automatically change this variable back to false
+ * before it yields.  Nobody else may set the variable to false.
+ *
+ * Access must be atomic for thread safety.
+ */
+bool qmp_dispatcher_co_busy;
+
+/*
+ * Protects mon_list, monitor_qapi_event_state, coroutine_mon,
+ * monitor_destroyed.
+ */
+QemuMutex monitor_lock;
+static GHashTable *monitor_qapi_event_state;
+static GHashTable *coroutine_mon; /* Maps Coroutine* to Monitor* */
+
+MonitorList mon_list;
+int mon_refcount;
+static bool monitor_destroyed;
+
+Monitor *monitor_cur(void)
+{
+    Monitor *mon;
+
+    qemu_mutex_lock(&monitor_lock);
+    mon = g_hash_table_lookup(coroutine_mon, qemu_coroutine_self());
+    qemu_mutex_unlock(&monitor_lock);
+
+    return mon;
+}
+
+/**
+ * Sets a new current monitor and returns the old one.
+ *
+ * If a non-NULL monitor is set for a coroutine, another call
+ * resetting it to NULL is required before the coroutine terminates,
+ * otherwise a stale entry would remain in the hash table.
+ */
+Monitor *monitor_set_cur(Coroutine *co, Monitor *mon)
+{
+    Monitor *old_monitor = monitor_cur();
+
+    qemu_mutex_lock(&monitor_lock);
+    if (mon) {
+        g_hash_table_replace(coroutine_mon, co, mon);
+    } else {
+        g_hash_table_remove(coroutine_mon, co);
+    }
+    qemu_mutex_unlock(&monitor_lock);
+
+    return old_monitor;
+}
+
+/**
+ * Is the current monitor, if any, a QMP monitor?
+ */
+bool monitor_cur_is_qmp(void)
+{
+    Monitor *cur_mon = monitor_cur();
+
+    return cur_mon && monitor_is_qmp(cur_mon);
+}
+
+/**
+ * Is @mon is using readline?
+ * Note: not all HMP monitors use readline, e.g., gdbserver has a
+ * non-interactive HMP monitor, so readline is not used there.
+ */
+static inline bool monitor_uses_readline(const MonitorHMP *mon)
+{
+    return mon->use_readline;
+}
+
+static inline bool monitor_is_hmp_non_interactive(const Monitor *mon)
+{
+    if (monitor_is_qmp(mon)) {
+        return false;
+    }
+
+    return !monitor_uses_readline(container_of(mon, MonitorHMP, common));
+}
+
+static void monitor_flush_locked(Monitor *mon);
+
+static gboolean monitor_unblocked(void *do_not_use, GIOCondition cond,
+                                  void *opaque)
+{
+    Monitor *mon = opaque;
+
+    qemu_mutex_lock(&mon->mon_lock);
+    mon->out_watch = 0;
+    monitor_flush_locked(mon);
+    qemu_mutex_unlock(&mon->mon_lock);
+    return FALSE;
+}
+
+/* Caller must hold mon->mon_lock */
+static void monitor_flush_locked(Monitor *mon)
+{
+    int rc;
+    size_t len;
+    const char *buf;
+
+    if (mon->skip_flush) {
+        return;
+    }
+
+    buf = mon->outbuf->str;
+    len = mon->outbuf->len;
+
+    if (len && !mon->mux_out) {
+        rc = qemu_chr_fe_write(&mon->chr, (const uint8_t *) buf, len);
+        if ((rc < 0 && errno != EAGAIN) || (rc == len)) {
+            /* all flushed or error */
+            g_string_truncate(mon->outbuf, 0);
+            return;
+        }
+        if (rc > 0) {
+            /* partial write */
+            g_string_erase(mon->outbuf, 0, rc);
+        }
+        if (mon->out_watch == 0) {
+            mon->out_watch =
+                qemu_chr_fe_add_watch(&mon->chr, G_IO_OUT | G_IO_HUP,
+                                      monitor_unblocked, mon);
+        }
+    }
+}
+
+void monitor_flush(Monitor *mon)
+{
+    qemu_mutex_lock(&mon->mon_lock);
+    monitor_flush_locked(mon);
+    qemu_mutex_unlock(&mon->mon_lock);
+}
+
+/* flush at every end of line */
+int monitor_puts(Monitor *mon, const char *str)
+{
+    int i;
+    char c;
+
+    qemu_mutex_lock(&mon->mon_lock);
+    for (i = 0; str[i]; i++) {
+        c = str[i];
+        if (c == '\n') {
+            g_string_append_c(mon->outbuf, '\r');
+        }
+        g_string_append_c(mon->outbuf, c);
+        if (c == '\n') {
+            monitor_flush_locked(mon);
+        }
+    }
+    qemu_mutex_unlock(&mon->mon_lock);
+
+    return i;
+}
+
+int monitor_vprintf(Monitor *mon, const char *fmt, va_list ap)
+{
+    char *buf;
+    int n;
+
+    if (!mon) {
+        return -1;
+    }
+
+    if (monitor_is_qmp(mon)) {
+        return -1;
+    }
+
+    buf = g_strdup_vprintf(fmt, ap);
+    n = monitor_puts(mon, buf);
+    g_free(buf);
+    return n;
+}
+
+int monitor_printf(Monitor *mon, const char *fmt, ...)
+{
+    int ret;
+
+    va_list ap;
+    va_start(ap, fmt);
+    ret = monitor_vprintf(mon, fmt, ap);
+    va_end(ap);
+    return ret;
+}
+
+/*
+ * Print to current monitor if we have one, else to stderr.
+ */
+int error_vprintf(const char *fmt, va_list ap)
+{
+    Monitor *cur_mon = monitor_cur();
+
+    if (cur_mon && !monitor_cur_is_qmp()) {
+        return monitor_vprintf(cur_mon, fmt, ap);
+    }
+    return vfprintf(stderr, fmt, ap);
+}
+
+int error_vprintf_unless_qmp(const char *fmt, va_list ap)
+{
+    Monitor *cur_mon = monitor_cur();
+
+    if (!cur_mon) {
+        return vfprintf(stderr, fmt, ap);
+    }
+    if (!monitor_cur_is_qmp()) {
+        return monitor_vprintf(cur_mon, fmt, ap);
+    }
+    return -1;
+}
+
+
+static MonitorQAPIEventConf monitor_qapi_event_conf[QAPI_EVENT__MAX] = {
+    /* Limit guest-triggerable events to 1 per second */
+    [QAPI_EVENT_RTC_CHANGE]        = { 1000 * SCALE_MS },
+    [QAPI_EVENT_WATCHDOG]          = { 1000 * SCALE_MS },
+    [QAPI_EVENT_BALLOON_CHANGE]    = { 1000 * SCALE_MS },
+    [QAPI_EVENT_QUORUM_REPORT_BAD] = { 1000 * SCALE_MS },
+    [QAPI_EVENT_QUORUM_FAILURE]    = { 1000 * SCALE_MS },
+    [QAPI_EVENT_VSERPORT_CHANGE]   = { 1000 * SCALE_MS },
+    [QAPI_EVENT_MEMORY_DEVICE_SIZE_CHANGE] = { 1000 * SCALE_MS },
+};
+
+/*
+ * Return the clock to use for recording an event's time.
+ * It's QEMU_CLOCK_REALTIME, except for qtests it's
+ * QEMU_CLOCK_VIRTUAL, to support testing rate limits.
+ * Beware: result is invalid before configure_accelerator().
+ */
+static inline QEMUClockType monitor_get_event_clock(void)
+{
+    return qtest_enabled() ? QEMU_CLOCK_VIRTUAL : QEMU_CLOCK_REALTIME;
+}
+
+/*
+ * Broadcast an event to all monitors.
+ * @qdict is the event object.  Its member "event" must match @event.
+ * Caller must hold monitor_lock.
+ */
+static void monitor_qapi_event_emit(QAPIEvent event, QDict *qdict)
+{
+    Monitor *mon;
+    MonitorQMP *qmp_mon;
+
+    trace_monitor_protocol_event_emit(event, qdict);
+    QTAILQ_FOREACH(mon, &mon_list, entry) {
+        if (!monitor_is_qmp(mon)) {
+            continue;
+        }
+
+        qmp_mon = container_of(mon, MonitorQMP, common);
+        if (qmp_mon->commands != &qmp_cap_negotiation_commands) {
+            qmp_send_response(qmp_mon, qdict);
+        }
+    }
+}
+
+static void monitor_qapi_event_handler(void *opaque);
+
+/*
+ * Queue a new event for emission to Monitor instances,
+ * applying any rate limiting if required.
+ */
+static void
+monitor_qapi_event_queue_no_reenter(QAPIEvent event, QDict *qdict)
+{
+    MonitorQAPIEventConf *evconf;
+    MonitorQAPIEventState *evstate;
+
+    assert(event < QAPI_EVENT__MAX);
+    evconf = &monitor_qapi_event_conf[event];
+    trace_monitor_protocol_event_queue(event, qdict, evconf->rate);
+
+    QEMU_LOCK_GUARD(&monitor_lock);
+
+    if (!evconf->rate) {
+        /* Unthrottled event */
+        monitor_qapi_event_emit(event, qdict);
+    } else {
+        QDict *data = qobject_to(QDict, qdict_get(qdict, "data"));
+        MonitorQAPIEventState key = { .event = event, .data = data };
+
+        evstate = g_hash_table_lookup(monitor_qapi_event_state, &key);
+        assert(!evstate || timer_pending(evstate->timer));
+
+        if (evstate) {
+            /*
+             * Timer is pending for (at least) evconf->rate ns after
+             * last send.  Store event for sending when timer fires,
+             * replacing a prior stored event if any.
+             */
+            qobject_unref(evstate->qdict);
+            evstate->qdict = qobject_ref(qdict);
+        } else {
+            /*
+             * Last send was (at least) evconf->rate ns ago.
+             * Send immediately, and arm the timer to call
+             * monitor_qapi_event_handler() in evconf->rate ns.  Any
+             * events arriving before then will be delayed until then.
+             */
+            int64_t now = qemu_clock_get_ns(monitor_get_event_clock());
+
+            monitor_qapi_event_emit(event, qdict);
+
+            evstate = g_new(MonitorQAPIEventState, 1);
+            evstate->event = event;
+            evstate->data = qobject_ref(data);
+            evstate->qdict = NULL;
+            evstate->timer = timer_new_ns(monitor_get_event_clock(),
+                                          monitor_qapi_event_handler,
+                                          evstate);
+            g_hash_table_add(monitor_qapi_event_state, evstate);
+            timer_mod_ns(evstate->timer, now + evconf->rate);
+        }
+    }
+}
+
+void qapi_event_emit(QAPIEvent event, QDict *qdict)
+{
+    /*
+     * monitor_qapi_event_queue_no_reenter() is not reentrant: it
+     * would deadlock on monitor_lock.  Work around by queueing
+     * events in thread-local storage.
+     * TODO: remove this, make it re-enter safe.
+     */
+    typedef struct MonitorQapiEvent {
+        QAPIEvent event;
+        QDict *qdict;
+        QSIMPLEQ_ENTRY(MonitorQapiEvent) entry;
+    } MonitorQapiEvent;
+    static __thread QSIMPLEQ_HEAD(, MonitorQapiEvent) event_queue;
+    static __thread bool reentered;
+    MonitorQapiEvent *ev;
+
+    if (!reentered) {
+        QSIMPLEQ_INIT(&event_queue);
+    }
+
+    ev = g_new(MonitorQapiEvent, 1);
+    ev->qdict = qobject_ref(qdict);
+    ev->event = event;
+    QSIMPLEQ_INSERT_TAIL(&event_queue, ev, entry);
+    if (reentered) {
+        return;
+    }
+
+    reentered = true;
+
+    while ((ev = QSIMPLEQ_FIRST(&event_queue)) != NULL) {
+        QSIMPLEQ_REMOVE_HEAD(&event_queue, entry);
+        monitor_qapi_event_queue_no_reenter(ev->event, ev->qdict);
+        qobject_unref(ev->qdict);
+        g_free(ev);
+    }
+
+    reentered = false;
+}
+
+/*
+ * This function runs evconf->rate ns after sending a throttled
+ * event.
+ * If another event has since been stored, send it.
+ */
+static void monitor_qapi_event_handler(void *opaque)
+{
+    MonitorQAPIEventState *evstate = opaque;
+    MonitorQAPIEventConf *evconf = &monitor_qapi_event_conf[evstate->event];
+
+    trace_monitor_protocol_event_handler(evstate->event, evstate->qdict);
+    QEMU_LOCK_GUARD(&monitor_lock);
+
+    if (evstate->qdict) {
+        int64_t now = qemu_clock_get_ns(monitor_get_event_clock());
+
+        monitor_qapi_event_emit(evstate->event, evstate->qdict);
+        qobject_unref(evstate->qdict);
+        evstate->qdict = NULL;
+        timer_mod_ns(evstate->timer, now + evconf->rate);
+    } else {
+        g_hash_table_remove(monitor_qapi_event_state, evstate);
+        qobject_unref(evstate->data);
+        timer_free(evstate->timer);
+        g_free(evstate);
+    }
+}
+
+static unsigned int qapi_event_throttle_hash(const void *key)
+{
+    const MonitorQAPIEventState *evstate = key;
+    unsigned int hash = evstate->event * 255;
+
+    if (evstate->event == QAPI_EVENT_VSERPORT_CHANGE) {
+        hash += g_str_hash(qdict_get_str(evstate->data, "id"));
+    }
+
+    if (evstate->event == QAPI_EVENT_QUORUM_REPORT_BAD) {
+        hash += g_str_hash(qdict_get_str(evstate->data, "node-name"));
+    }
+
+    if (evstate->event == QAPI_EVENT_MEMORY_DEVICE_SIZE_CHANGE) {
+        hash += g_str_hash(qdict_get_str(evstate->data, "qom-path"));
+    }
+
+    return hash;
+}
+
+static gboolean qapi_event_throttle_equal(const void *a, const void *b)
+{
+    const MonitorQAPIEventState *eva = a;
+    const MonitorQAPIEventState *evb = b;
+
+    if (eva->event != evb->event) {
+        return FALSE;
+    }
+
+    if (eva->event == QAPI_EVENT_VSERPORT_CHANGE) {
+        return !strcmp(qdict_get_str(eva->data, "id"),
+                       qdict_get_str(evb->data, "id"));
+    }
+
+    if (eva->event == QAPI_EVENT_QUORUM_REPORT_BAD) {
+        return !strcmp(qdict_get_str(eva->data, "node-name"),
+                       qdict_get_str(evb->data, "node-name"));
+    }
+
+    if (eva->event == QAPI_EVENT_MEMORY_DEVICE_SIZE_CHANGE) {
+        return !strcmp(qdict_get_str(eva->data, "qom-path"),
+                       qdict_get_str(evb->data, "qom-path"));
+    }
+
+    return TRUE;
+}
+
+int monitor_suspend(Monitor *mon)
+{
+    if (monitor_is_hmp_non_interactive(mon)) {
+        return -ENOTTY;
+    }
+
+    qatomic_inc(&mon->suspend_cnt);
+
+    if (mon->use_io_thread) {
+        /*
+         * Kick I/O thread to make sure this takes effect.  It'll be
+         * evaluated again in prepare() of the watch object.
+         */
+        aio_notify(iothread_get_aio_context(mon_iothread));
+    }
+
+    trace_monitor_suspend(mon, 1);
+    return 0;
+}
+
+static void monitor_accept_input(void *opaque)
+{
+    Monitor *mon = opaque;
+
+    qemu_chr_fe_accept_input(&mon->chr);
+}
+
+void monitor_resume(Monitor *mon)
+{
+    if (monitor_is_hmp_non_interactive(mon)) {
+        return;
+    }
+
+    if (qatomic_dec_fetch(&mon->suspend_cnt) == 0) {
+        AioContext *ctx;
+
+        if (mon->use_io_thread) {
+            ctx = iothread_get_aio_context(mon_iothread);
+        } else {
+            ctx = qemu_get_aio_context();
+        }
+
+        if (!monitor_is_qmp(mon)) {
+            MonitorHMP *hmp_mon = container_of(mon, MonitorHMP, common);
+            assert(hmp_mon->rs);
+            readline_show_prompt(hmp_mon->rs);
+        }
+
+        aio_bh_schedule_oneshot(ctx, monitor_accept_input, mon);
+    }
+
+    trace_monitor_suspend(mon, -1);
+}
+
+int monitor_can_read(void *opaque)
+{
+    Monitor *mon = opaque;
+
+    return !qatomic_mb_read(&mon->suspend_cnt);
+}
+
+void monitor_list_append(Monitor *mon)
+{
+    qemu_mutex_lock(&monitor_lock);
+    /*
+     * This prevents inserting new monitors during monitor_cleanup().
+     * A cleaner solution would involve the main thread telling other
+     * threads to terminate, waiting for their termination.
+     */
+    if (!monitor_destroyed) {
+        QTAILQ_INSERT_HEAD(&mon_list, mon, entry);
+        mon = NULL;
+    }
+    qemu_mutex_unlock(&monitor_lock);
+
+    if (mon) {
+        monitor_data_destroy(mon);
+        g_free(mon);
+    }
+}
+
+static void monitor_iothread_init(void)
+{
+    mon_iothread = iothread_create("mon_iothread", &error_abort);
+}
+
+void monitor_data_init(Monitor *mon, bool is_qmp, bool skip_flush,
+                       bool use_io_thread)
+{
+    if (use_io_thread && !mon_iothread) {
+        monitor_iothread_init();
+    }
+    qemu_mutex_init(&mon->mon_lock);
+    mon->is_qmp = is_qmp;
+    mon->outbuf = g_string_new(NULL);
+    mon->skip_flush = skip_flush;
+    mon->use_io_thread = use_io_thread;
+}
+
+void monitor_data_destroy(Monitor *mon)
+{
+    g_free(mon->mon_cpu_path);
+    qemu_chr_fe_deinit(&mon->chr, false);
+    if (monitor_is_qmp(mon)) {
+        monitor_data_destroy_qmp(container_of(mon, MonitorQMP, common));
+    } else {
+        readline_free(container_of(mon, MonitorHMP, common)->rs);
+    }
+    g_string_free(mon->outbuf, true);
+    qemu_mutex_destroy(&mon->mon_lock);
+}
+
+void monitor_cleanup(void)
+{
+    /*
+     * The dispatcher needs to stop before destroying the monitor and
+     * the I/O thread.
+     *
+     * We need to poll both qemu_aio_context and iohandler_ctx to make
+     * sure that the dispatcher coroutine keeps making progress and
+     * eventually terminates.  qemu_aio_context is automatically
+     * polled by calling AIO_WAIT_WHILE on it, but we must poll
+     * iohandler_ctx manually.
+     *
+     * Letting the iothread continue while shutting down the dispatcher
+     * means that new requests may still be coming in. This is okay,
+     * we'll just leave them in the queue without sending a response
+     * and monitor_data_destroy() will free them.
+     */
+    qmp_dispatcher_co_shutdown = true;
+    if (!qatomic_xchg(&qmp_dispatcher_co_busy, true)) {
+        aio_co_wake(qmp_dispatcher_co);
+    }
+
+    AIO_WAIT_WHILE(qemu_get_aio_context(),
+                   (aio_poll(iohandler_get_aio_context(), false),
+                    qatomic_mb_read(&qmp_dispatcher_co_busy)));
+
+    /*
+     * We need to explicitly stop the I/O thread (but not destroy it),
+     * clean up the monitor resources, then destroy the I/O thread since
+     * we need to unregister from chardev below in
+     * monitor_data_destroy(), and chardev is not thread-safe yet
+     */
+    if (mon_iothread) {
+        iothread_stop(mon_iothread);
+    }
+
+    /* Flush output buffers and destroy monitors */
+    qemu_mutex_lock(&monitor_lock);
+    monitor_destroyed = true;
+    while (!QTAILQ_EMPTY(&mon_list)) {
+        Monitor *mon = QTAILQ_FIRST(&mon_list);
+        QTAILQ_REMOVE(&mon_list, mon, entry);
+        /* Permit QAPI event emission from character frontend release */
+        qemu_mutex_unlock(&monitor_lock);
+        monitor_flush(mon);
+        monitor_data_destroy(mon);
+        qemu_mutex_lock(&monitor_lock);
+        g_free(mon);
+    }
+    qemu_mutex_unlock(&monitor_lock);
+
+    if (mon_iothread) {
+        iothread_destroy(mon_iothread);
+        mon_iothread = NULL;
+    }
+}
+
+static void monitor_qapi_event_init(void)
+{
+    monitor_qapi_event_state = g_hash_table_new(qapi_event_throttle_hash,
+                                                qapi_event_throttle_equal);
+}
+
+void monitor_init_globals_core(void)
+{
+    monitor_qapi_event_init();
+    qemu_mutex_init(&monitor_lock);
+    coroutine_mon = g_hash_table_new(NULL, NULL);
+
+    /*
+     * The dispatcher BH must run in the main loop thread, since we
+     * have commands assuming that context.  It would be nice to get
+     * rid of those assumptions.
+     */
+    qmp_dispatcher_co = qemu_coroutine_create(monitor_qmp_dispatcher_co, NULL);
+    qatomic_mb_set(&qmp_dispatcher_co_busy, true);
+    aio_co_schedule(iohandler_get_aio_context(), qmp_dispatcher_co);
+}
+
+int monitor_init(MonitorOptions *opts, bool allow_hmp, Error **errp)
+{
+    Chardev *chr;
+    Error *local_err = NULL;
+
+    chr = qemu_chr_find(opts->chardev);
+    if (chr == NULL) {
+        error_setg(errp, "chardev \"%s\" not found", opts->chardev);
+        return -1;
+    }
+
+    if (!opts->has_mode) {
+        opts->mode = allow_hmp ? MONITOR_MODE_READLINE : MONITOR_MODE_CONTROL;
+    }
+
+    switch (opts->mode) {
+    case MONITOR_MODE_CONTROL:
+        monitor_init_qmp(chr, opts->pretty, &local_err);
+        break;
+    case MONITOR_MODE_READLINE:
+        if (!allow_hmp) {
+            error_setg(errp, "Only QMP is supported");
+            return -1;
+        }
+        if (opts->pretty) {
+            error_setg(errp, "'pretty' is not compatible with HMP monitors");
+            return -1;
+        }
+        monitor_init_hmp(chr, true, &local_err);
+        break;
+    default:
+        g_assert_not_reached();
+    }
+
+    if (local_err) {
+        error_propagate(errp, local_err);
+        return -1;
+    }
+    return 0;
+}
+
+int monitor_init_opts(QemuOpts *opts, Error **errp)
+{
+    Visitor *v;
+    MonitorOptions *options;
+    int ret;
+
+    v = opts_visitor_new(opts);
+    visit_type_MonitorOptions(v, NULL, &options, errp);
+    visit_free(v);
+    if (!options) {
+        return -1;
+    }
+
+    ret = monitor_init(options, true, errp);
+    qapi_free_MonitorOptions(options);
+    return ret;
+}
+
+QemuOptsList qemu_mon_opts = {
+    .name = "mon",
+    .implied_opt_name = "chardev",
+    .head = QTAILQ_HEAD_INITIALIZER(qemu_mon_opts.head),
+    .desc = {
+        {
+            .name = "mode",
+            .type = QEMU_OPT_STRING,
+        },{
+            .name = "chardev",
+            .type = QEMU_OPT_STRING,
+        },{
+            .name = "pretty",
+            .type = QEMU_OPT_BOOL,
+        },
+        { /* end of list */ }
+    },
+};