[udev] Ignore stale events received while blocked in mode transition

Mode transition blocks udev event processing. If user disconnects and
reconnects the cable multiple times during the blockade, usb-moded
will act on stale events that might not reflect the actual state of
the usb connection.

Handle disconnects immediately, but delay acting on connects so that
sequences of multiple disconnects and connects get compressed into
single transition to undefined mode possibly followed by single
transition to appropriated connected mode.

Signed-off-by: Simo Piiroinen <simo.piiroinen@jollamobile.com>

src/usb_moded-udev.c

@@ -54,7 +54,7 @@
 
 static gboolean      umudev_cable_state_timer_cb   (gpointer aptr);
 static void          umudev_cable_state_stop_timer (void);
-static void          umudev_cable_state_start_timer(void);
+static void          umudev_cable_state_start_timer(gint delay);
 static bool          umudev_cable_state_connected  (void);
 static cable_state_t umudev_cable_state_get        (void);
 static void          umudev_cable_state_set        (cable_state_t state);
@@ -90,6 +90,7 @@ static cable_state_t umudev_cable_state_previous = CABLE_STATE_UNKNOWN;
 
 /** Timer id for delaying: reported by udev -> active in usb-moded */
 static guint umudev_cable_state_timer_id = 0;
+static gint  umudev_cable_state_timer_delay = -1;
 
 /* ========================================================================= *
  * cable state
@@ -99,6 +100,7 @@ static gboolean umudev_cable_state_timer_cb(gpointer aptr)
 {
     (void)aptr;
     umudev_cable_state_timer_id = 0;
+    umudev_cable_state_timer_delay = -1;
 
     log_debug("trigger delayed transfer to: %s",
               cable_state_repr(umudev_cable_state_current));
@@ -113,17 +115,23 @@ static void umudev_cable_state_stop_timer(void)
                   cable_state_repr(umudev_cable_state_current));
         g_source_remove(umudev_cable_state_timer_id),
             umudev_cable_state_timer_id = 0;
+        umudev_cable_state_timer_delay = -1;
     }
 }
 
-static void umudev_cable_state_start_timer(void)
+static void umudev_cable_state_start_timer(gint delay)
 {
+    if( umudev_cable_state_timer_delay != delay ) {
+        umudev_cable_state_stop_timer();
+    }
+
     if( !umudev_cable_state_timer_id ) {
         log_debug("schedule delayed transfer to: %s",
                   cable_state_repr(umudev_cable_state_current));
         umudev_cable_state_timer_id =
-            g_timeout_add(usbmoded_cable_connection_delay,
+            g_timeout_add(delay,
                           umudev_cable_state_timer_cb, 0);
+        umudev_cable_state_timer_delay = delay;
     }
 }
 
@@ -222,10 +230,33 @@ static void umudev_cable_state_from_udev(cable_state_t curr)
               cable_state_repr(prev),
               cable_state_repr(curr));
 
-    if( curr == CABLE_STATE_PC_CONNECTED && prev != CABLE_STATE_UNKNOWN )
-        umudev_cable_state_start_timer();
-    else
+    /* Because mode transitions are handled synchronously and can thus
+     * block the usb-moded mainloop, we might end up receiving a bursts
+     * of stale udev events after returning from mode switch - including
+     * multiple cable connect / disconnect events due to user replugging
+     * the cable in frustration of things taking too long.
+     */
+
+    if( curr == CABLE_STATE_DISCONNECTED ) {
+        /* If we see any disconnect events, those must be acted on
+         * immediately to get the 1st disconnect handled.
+         */
         umudev_cable_state_set(curr);
+    }
+    else {
+        /* All other transitions are handled with at least 100 ms delay.
+         * This should compress multiple stale disconnect + connect
+         * pairs into single action.
+         */
+        gint delay = 100;
+
+        if( curr == CABLE_STATE_PC_CONNECTED && prev != CABLE_STATE_UNKNOWN ) {
+            if( delay < usbmoded_cable_connection_delay )
+                delay = usbmoded_cable_connection_delay;
+        }
+
+        umudev_cable_state_start_timer(delay);
+    }
 
 EXIT:
     return;