[PATCH v3 1/2] qmp: Support chardev-change for QMP device

[PATCH v3 1/2] qmp: Support chardev-change for QMP device

[Li Zhang]

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 according.
  * refactor the source code of chardev.

 monitor/monitor-internal.h |  1 +
 monitor/monitor.c          |  4 +-
 monitor/qmp.c              | 83 +++++++++++++++++++++++++++-----------
 3 files changed, 62 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..92c704373f 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 mointor_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 +522,14 @@ 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);
+
+    if (!mointor_in_list(&mon->common))
+        monitor_list_append(&mon->common);
 }
 
-void monitor_init_qmp(Chardev *chr, bool pretty, Error **errp)
+static void monitor_backend_init(MonitorQMP *mon, Chardev *chr)
 {
-    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);
     if (mon->common.use_io_thread) {
         /*
          * Make sure the old iowatch is gone.  It's possible when
@@ -532,7 +547,29 @@ 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 (!mointor_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

[PATCH v3 2/2] chardev: refactor qmp_chardev_add and qmp_chardev_change

[Li Zhang]

To improve the problematic source code as Markus mentioned
before and some redundant source code, it is refactored
in the functions qmp_chardev_add and qmp_chardev_change.
https://lists.nongnu.org/archive/html/qemu-devel/2021-04/msg03167.html

Signed-off-by: Li Zhang <li.zhang@ionos.com>
---
 chardev/char.c | 72 ++++++++++++++++++++++++++------------------------
 1 file changed, 37 insertions(+), 35 deletions(-)

diff --git a/chardev/char.c b/chardev/char.c
index d959eec522..da23e1bd71 100644
--- a/chardev/char.c
+++ b/chardev/char.c
@@ -1028,23 +1028,10 @@ Chardev *qemu_chardev_new(const char *id, const char *typename,
     return chr;
 }
 
-ChardevReturn *qmp_chardev_add(const char *id, ChardevBackend *backend,
-                               Error **errp)
+static ChardevReturn *chardev_add(const char *id, Chardev *chr,
+                                  Error **errp)
 {
-    const ChardevClass *cc;
     ChardevReturn *ret;
-    Chardev *chr;
-
-    cc = char_get_class(ChardevBackendKind_str(backend->type), errp);
-    if (!cc) {
-        return NULL;
-    }
-
-    chr = chardev_new(id, object_class_get_name(OBJECT_CLASS(cc)),
-                      backend, NULL, false, errp);
-    if (!chr) {
-        return NULL;
-    }
 
     if (!object_property_try_add_child(get_chardevs_root(), id, OBJECT(chr),
                                        errp)) {
@@ -1062,6 +1049,26 @@ ChardevReturn *qmp_chardev_add(const char *id, ChardevBackend *backend,
     return ret;
 }
 
+ChardevReturn *qmp_chardev_add(const char *id, ChardevBackend *backend,
+                               Error **errp)
+{
+    const ChardevClass *cc;
+    Chardev *chr;
+
+    cc = char_get_class(ChardevBackendKind_str(backend->type), errp);
+    if (!cc) {
+        return NULL;
+    }
+
+    chr = chardev_new(id, object_class_get_name(OBJECT_CLASS(cc)),
+                      backend, NULL, false, errp);
+    if (!chr) {
+        return NULL;
+    }
+
+    return chardev_add(id, chr, errp);
+}
+
 ChardevReturn *qmp_chardev_change(const char *id, ChardevBackend *backend,
                                   Error **errp)
 {
@@ -1070,7 +1077,6 @@ ChardevReturn *qmp_chardev_change(const char *id, ChardevBackend *backend,
     Chardev *chr, *chr_new;
     bool closed_sent = false;
     bool handover_yank_instance;
-    ChardevReturn *ret;
 
     chr = qemu_chr_find(id);
     if (!chr) {
@@ -1078,6 +1084,12 @@ ChardevReturn *qmp_chardev_change(const char *id, ChardevBackend *backend,
         return NULL;
     }
 
+    cc = CHARDEV_GET_CLASS(chr);
+    cc_new = char_get_class(ChardevBackendKind_str(backend->type), errp);
+    if (!cc_new) {
+        return NULL;
+    }
+
     if (CHARDEV_IS_MUX(chr)) {
         error_setg(errp, "Mux device hotswap not supported yet");
         return NULL;
@@ -1092,8 +1104,13 @@ ChardevReturn *qmp_chardev_change(const char *id, ChardevBackend *backend,
     be = chr->be;
     if (!be) {
         /* easy case */
-        object_unparent(OBJECT(chr));
-        return qmp_chardev_add(id, backend, errp);
+        chr_new = chardev_new(id, object_class_get_name(OBJECT_CLASS(cc_new)),
+                              backend, NULL, false, errp);
+        if (!chr_new) {
+            return NULL;
+        }
+
+        goto out;
     }
 
     if (!be->chr_be_change) {
@@ -1101,12 +1118,6 @@ ChardevReturn *qmp_chardev_change(const char *id, ChardevBackend *backend,
         return NULL;
     }
 
-    cc = CHARDEV_GET_CLASS(chr);
-    cc_new = char_get_class(ChardevBackendKind_str(backend->type), errp);
-    if (!cc_new) {
-        return NULL;
-    }
-
     /*
      * The new chardev should not register a yank instance if the current
      * chardev has registered one already.
@@ -1147,18 +1158,9 @@ ChardevReturn *qmp_chardev_change(const char *id, ChardevBackend *backend,
      */
     chr->handover_yank_instance = handover_yank_instance;
 
+out:
     object_unparent(OBJECT(chr));
-    object_property_add_child(get_chardevs_root(), chr_new->label,
-                              OBJECT(chr_new));
-    object_unref(OBJECT(chr_new));
-
-    ret = g_new0(ChardevReturn, 1);
-    if (CHARDEV_IS_PTY(chr_new)) {
-        ret->pty = g_strdup(chr_new->filename + 4);
-        ret->has_pty = true;
-    }
-
-    return ret;
+    return chardev_add(id, chr_new, errp);
 }
 
 void qmp_chardev_remove(const char *id, Error **errp)
-- 
2.25.1

Re: [PATCH v3 1/2] qmp: Support chardev-change for QMP device

[Li Zhang]

Hi Markus,

Sorry for the late update because of other tasks. Please review the patcheset.
About the indentation problem, I found that the email shows different
from my patches.
The source code which is not changed also shows different indentation
in email.
I checked a lot of times, I still don't know what the problem is.

On Tue, Jul 6, 2021 at 9:15 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 according.
>   * refactor the source code of chardev.
>
>  monitor/monitor-internal.h |  1 +
>  monitor/monitor.c          |  4 +-
>  monitor/qmp.c              | 83 +++++++++++++++++++++++++++-----------
>  3 files changed, 62 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..92c704373f 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 mointor_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 +522,14 @@ 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);
> +
> +    if (!mointor_in_list(&mon->common))
> +        monitor_list_append(&mon->common);
>  }
>
> -void monitor_init_qmp(Chardev *chr, bool pretty, Error **errp)
> +static void monitor_backend_init(MonitorQMP *mon, Chardev *chr)
>  {
> -    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);
>      if (mon->common.use_io_thread) {
>          /*
>           * Make sure the old iowatch is gone.  It's possible when
> @@ -532,7 +547,29 @@ 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 (!mointor_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