[Qemu-devel] [PATCH v7 13/23] monitor: let suspend/resume work even with QMPs

[Peter Xu <peterx@redhat.com>]

This patches allows QMP monitors to be suspended/resumed.

One thing to mention is that for QMPs that are using IOThreads, we need
an explicit kick for the IOThread in case it is sleeping.

Meanwhile, we need to take special care on non-interactive HMPs.
Currently only gdbserver is using that.  For these monitors, we still
don't allow suspend/resume operations.

Since at it, add traces for the operations.

Signed-off-by: Peter Xu <peterx@redhat.com>
---
 monitor.c    | 45 ++++++++++++++++++++++++++++++++++++++++++---
 trace-events |  1 +
 2 files changed, 43 insertions(+), 3 deletions(-)

diff --git a/monitor.c b/monitor.c
index 60bcf67b3a..76137ba2a4 100644
--- a/monitor.c
+++ b/monitor.c
@@ -246,6 +246,21 @@ static inline bool monitor_is_qmp(const Monitor *mon)
     return (mon->flags & MONITOR_USE_CONTROL);
 }
 
+/**
+ * Whether @mon is using readline?  Note: not all HMP monitors can are
+ * using readline, e.g., gdbserver has non-interactive HMP monitor, so
+ * readline is not used there.
+ */
+static inline bool monitor_uses_readline(const Monitor *mon)
+{
+    return mon->flags & MONITOR_USE_READLINE;
+}
+
+static inline bool monitor_is_hmp_non_interactive(const Monitor *mon)
+{
+    return !monitor_is_qmp(mon) && !monitor_uses_readline(mon);
+}
+
 /**
  * Is the current monitor, if any, a QMP monitor?
  */
@@ -3994,19 +4009,43 @@ static void monitor_command_cb(void *opaque, const char *cmdline,
 
 int monitor_suspend(Monitor *mon)
 {
-    if (!mon->rs)
+    if (monitor_is_hmp_non_interactive(mon)) {
         return -ENOTTY;
+    }
+
+    if (monitor_is_qmp(mon)) {
+        /*
+         * Kick iothread to make sure this takes effect.  It'll be
+         * evaluated again in prepare() of the watch object.
+         */
+        aio_notify(iothread_get_aio_context(mon_global.mon_iothread));
+    }
     atomic_inc(&mon->suspend_cnt);
+    trace_monitor_suspend(mon, 1);
     return 0;
 }
 
 void monitor_resume(Monitor *mon)
 {
-    if (!mon->rs)
+    if (monitor_is_hmp_non_interactive(mon)) {
         return;
+    }
+
     if (atomic_dec_fetch(&mon->suspend_cnt) == 0) {
-        readline_show_prompt(mon->rs);
+        if (monitor_is_qmp(mon)) {
+            /*
+             * For QMP monitors that are running in IOThread, let's
+             * kick the thread in case it's sleeping.
+             */
+            if (mon->use_io_thr) {
+                aio_notify(iothread_get_aio_context(mon_global.mon_iothread));
+            }
+        } else {
+            assert(mon->rs);
+            readline_show_prompt(mon->rs);
+        }
     }
+    trace_monitor_suspend(mon, -1);
 }
 
 static QObject *get_qmp_greeting(Monitor *mon)
diff --git a/trace-events b/trace-events
index ec95e67089..eecb68b1d5 100644
--- a/trace-events
+++ b/trace-events
@@ -47,6 +47,7 @@ monitor_protocol_event_emit(uint32_t event, void *data) "event=%d data=%p"
 monitor_protocol_event_queue(uint32_t event, void *qdict, uint64_t rate) "event=%d data=%p rate=%" PRId64
 handle_hmp_command(void *mon, const char *cmdline) "mon %p cmdline: %s"
 handle_qmp_command(void *mon, const char *req) "mon %p req: %s"
+monitor_suspend(void *ptr, int cnt) "mon %p: %d"
 
 # dma-helpers.c
 dma_blk_io(void *dbs, void *bs, int64_t offset, bool to_dev) "dbs=%p bs=%p offset=%" PRId64 " to_dev=%d"
-- 
2.14.3