Only decrement buttonsDown when the button count is greater than 0.

Device drivers flush their buttons on device init and cause a button down
event to be generated. If we unconditionally decrease the buttons, we won't be
able to ever get a passive device grab.

Format documentation for CheckDeviceGrabs to make it readable.
(cherry picked from commit 3e894974cdd6a75683d4601f71622d1da7ec4395)

Conflicts:

	Xi/exevents.c

2 files changed, 25 insertions, 12 deletions

diff --git a/Xi/exevents.c b/Xi/exevents.c
index 9e71a9e4e..fe297ab6a 100644
--- a/Xi/exevents.c
+++ b/Xi/exevents.c
@@ -248,7 +248,9 @@ ProcessOtherEvent(xEventPtr xE, DeviceIntPtr other, int count)
 	SetMaskForEvent(Motion_Filter(b), DeviceMotionNotify);
 	if (!grab)
 	    if (CheckDeviceGrabs(other, xE, 0, count))
-		return;
+                /* if a passive grab was activated, the event has been sent
+                 * already */
+                return;
 
     } else if (xE->u.u.type == DeviceButtonRelease) {
         if (!b)
@@ -258,7 +260,7 @@ ProcessOtherEvent(xEventPtr xE, DeviceIntPtr other, int count)
 	*kptr &= ~bit;
 	if (other->valuator)
 	    other->valuator->motionHintWindow = NullWindow;
-	if (!--b->buttonsDown)
+        if (b->buttonsDown >= 1 && !--b->buttonsDown)
 	    b->motionMask = 0;
 	xE->u.u.detail = b->map[key];
 	if (xE->u.u.detail == 0)
diff --git a/dix/events.c b/dix/events.c
index 887cbcd68..63bc3799d 100644
--- a/dix/events.c
+++ b/dix/events.c
@@ -2629,6 +2629,7 @@ BorderSizeNotEmpty(WindowPtr pWin)
 /** 
  * "CheckPassiveGrabsOnWindow" checks to see if the event passed in causes a
  * passive grab set on the window to be activated. 
+ * If a passive grab is activated, the event will be delivered to the client.
  * 
  * @param pWin The window that may be subject to a passive grab.
  * @param device Device that caused the event.
@@ -2728,16 +2729,26 @@ CheckPassiveGrabsOnWindow(
 }
 
 /**
-"CheckDeviceGrabs" handles both keyboard and pointer events that may cause
-a passive grab to be activated.  If the event is a keyboard event, the
-ancestors of the focus window are traced down and tried to see if they have
-any passive grabs to be activated.  If the focus window itself is reached and
-it's descendants contain they pointer, the ancestors of the window that the
-pointer is in are then traced down starting at the focus window, otherwise no
-grabs are activated.  If the event is a pointer event, the ancestors of the
-window that the pointer is in are traced down starting at the root until
-CheckPassiveGrabs causes a passive grab to activate or all the windows are
-tried. PRH
+ * CheckDeviceGrabs handles both keyboard and pointer events that may cause
+ * a passive grab to be activated.  
+ *
+ * If the event is a keyboard event, the ancestors of the focus window are
+ * traced down and tried to see if they have any passive grabs to be
+ * activated.  If the focus window itself is reached and it's descendants
+ * contain the pointer, the ancestors of the window that the pointer is in
+ * are then traced down starting at the focus window, otherwise no grabs are
+ * activated.  
+ * If the event is a pointer event, the ancestors of the window that the
+ * pointer is in are traced down starting at the root until CheckPassiveGrabs
+ * causes a passive grab to activate or all the windows are
+ * tried. PRH
+ *
+ * If a grab is activated, the event has been sent to the client already!
+ *
+ * @param device The device that caused the event.
+ * @param xE The event to handle (most likely {Device}ButtonPress).
+ * @param count Number of events in list.
+ * @return TRUE if a grab has been activated or false otherwise.
 */
 
 Bool