For some scenarios, we'd like to hot-add a monitor device. But QEMU doesn't support that, yet. It does support hot-swapping character backends with QMP command chardev-change. This lets us pre-add a monitor with a null character backend, then chardev-change to a socket backend. Except the chardev-change fails with "Chardev user does not support chardev hotswap" because monitors don't provide the required callback. Implement it for QMP monitors.
Signed-off-by: Li Zhang <li.zh...@ionos.com> --- v3 -> v2: * Rework the patch which is to add hotswap for QMP device https://lists.nongnu.org/archive/html/qemu-devel/2021-04/msg03167.html * Refactor the functions qmp_chardev_add and qmp_chardev_change monitor/monitor-internal.h | 1 + monitor/monitor.c | 4 +- monitor/qmp.c | 84 +++++++++++++++++++++++++++----------- 3 files changed, 63 insertions(+), 26 deletions(-) diff --git a/monitor/monitor-internal.h b/monitor/monitor-internal.h index 9c3a09cb01..162f73119b 100644 --- a/monitor/monitor-internal.h +++ b/monitor/monitor-internal.h @@ -182,5 +182,6 @@ int get_monitor_def(Monitor *mon, int64_t *pval, const char *name); void help_cmd(Monitor *mon, const char *name); void handle_hmp_command(MonitorHMP *mon, const char *cmdline); int hmp_compare_cmd(const char *name, const char *list); +void monitor_flush_locked(Monitor *mon); #endif diff --git a/monitor/monitor.c b/monitor/monitor.c index b90c0f4051..1b05ef3bdb 100644 --- a/monitor/monitor.c +++ b/monitor/monitor.c @@ -154,8 +154,6 @@ static inline bool monitor_is_hmp_non_interactive(const Monitor *mon) return !monitor_uses_readline(container_of(mon, MonitorHMP, common)); } -static void monitor_flush_locked(Monitor *mon); - static gboolean monitor_unblocked(GIOChannel *chan, GIOCondition cond, void *opaque) { @@ -169,7 +167,7 @@ static gboolean monitor_unblocked(GIOChannel *chan, GIOCondition cond, } /* Caller must hold mon->mon_lock */ -static void monitor_flush_locked(Monitor *mon) +void monitor_flush_locked(Monitor *mon) { int rc; size_t len; diff --git a/monitor/qmp.c b/monitor/qmp.c index 092c527b6f..29b49ee041 100644 --- a/monitor/qmp.c +++ b/monitor/qmp.c @@ -46,6 +46,8 @@ struct QMPRequest { typedef struct QMPRequest QMPRequest; QmpCommandList qmp_commands, qmp_cap_negotiation_commands; +static void monitor_qmp_setup_handlers_bh(void *opaque); +static void monitor_backend_init(MonitorQMP *mon, Chardev *chr); static bool qmp_oob_enabled(MonitorQMP *mon) { @@ -481,6 +483,35 @@ void monitor_data_destroy_qmp(MonitorQMP *mon) g_queue_free(mon->qmp_requests); } +static bool monitor_in_list(Monitor *mon) +{ + Monitor *mon_tmp; + QTAILQ_FOREACH(mon_tmp, &mon_list, entry) { + if (mon_tmp == mon) { + return true; + } + } + return false; +} + +static int monitor_qmp_change(void *opaque) +{ + MonitorQMP *mon = opaque; + + monitor_data_init(&mon->common, true, false, + qemu_chr_has_feature(mon->common.chr.chr, + QEMU_CHAR_FEATURE_GCONTEXT)); + monitor_backend_init(mon, mon->common.chr.chr); + qemu_mutex_lock(&mon->common.mon_lock); + if (mon->common.out_watch) { + mon->common.out_watch = 0; + monitor_flush_locked(&mon->common); + } + qemu_mutex_unlock(&mon->common.mon_lock); + + return 0; +} + static void monitor_qmp_setup_handlers_bh(void *opaque) { MonitorQMP *mon = opaque; @@ -491,30 +522,15 @@ static void monitor_qmp_setup_handlers_bh(void *opaque) 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); -} + monitor_qmp_change, &mon->common, context, true); -void monitor_init_qmp(Chardev *chr, bool pretty, Error **errp) -{ - MonitorQMP *mon = g_new0(MonitorQMP, 1); - - if (!qemu_chr_fe_init(&mon->common.chr, chr, errp)) { - g_free(mon); - return; + if (!monitor_in_list(&mon->common)) { + monitor_list_append(&mon->common); } - qemu_chr_fe_set_echo(&mon->common.chr, true); - - /* 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(); +} - json_message_parser_init(&mon->parser, handle_qmp_command, mon, NULL); +static void monitor_backend_init(MonitorQMP *mon, Chardev *chr) +{ if (mon->common.use_io_thread) { /* * Make sure the old iowatch is gone. It's possible when @@ -532,7 +548,29 @@ void monitor_init_qmp(Chardev *chr, bool pretty, Error **errp) } 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); + monitor_qmp_change, &mon->common, NULL, true); + if (!monitor_in_list(&mon->common)) { + monitor_list_append(&mon->common); + } } } + +void monitor_init_qmp(Chardev *chr, bool pretty, Error **errp) +{ + MonitorQMP *mon = g_new0(MonitorQMP, 1); + + if (!qemu_chr_fe_init(&mon->common.chr, chr, errp)) { + g_free(mon); + return; + } + qemu_chr_fe_set_echo(&mon->common.chr, true); + /* 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(); + json_message_parser_init(&mon->parser, handle_qmp_command, mon, NULL); + monitor_backend_init(mon, chr); +} -- 2.25.1