Re: [PATCH v3 RESEND 1/2] qmp: Support chardev-change

[Li Zhang]

Ping

On Fri, Jul 9, 2021 at 6:11 PM Li Zhang <zhlcindy@gmail.com> wrote:
>
> 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.zhang@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
>


-- 

Best Regards
-Li