dix: if we run out of space for new touch events, resize the queue

The SIGIO handler forces us to drop the current touch and schedule the
actual resize for later. Should not happen if the device sets up the
TouchClassRec with the correct number of touchpoints.

Co-authored-by: Daniel Stone <daniel@fooishbar.org>
Signed-off-by: Peter Hutterer <peter.hutterer@who-t.net>
Reviewed-by: Chase Douglas <chase.douglas@canonical.com>

1 files changed, 67 insertions, 1 deletions

diff --git a/dix/touch.c b/dix/touch.c
index f9d16172b..b492e8238 100644
--- a/dix/touch.c
+++ b/dix/touch.c
@@ -34,6 +34,9 @@
 #include "eventstr.h"
 #include "exevents.h"
 
+/* If a touch queue resize is needed, the device id's bit is set. */
+static unsigned char resize_waiting[(MAXDEVICES + 7)/8];
+
 /**
  * Some documentation about touch points:
  * The driver submits touch events with it's own (unique) touch point ID.
@@ -54,6 +57,60 @@
  */
 
 /**
+ * Check which devices need a bigger touch event queue and grow their
+ * last.touches by half it's current size.
+ *
+ * @param client Always the serverClient
+ * @param closure Always NULL
+ *
+ * @return Always True. If we fail to grow we probably will topple over soon
+ * anyway and re-executing this won't help.
+ */
+static Bool
+TouchResizeQueue(ClientPtr client, pointer closure)
+{
+    int i;
+
+    OsBlockSignals();
+
+    /* first two ids are reserved */
+    for (i = 2; i < MAXDEVICES; i++)
+    {
+        DeviceIntPtr dev;
+        DDXTouchPointInfoPtr tmp;
+        size_t size;
+
+        if (!BitIsOn(resize_waiting, i))
+            continue;
+
+        ClearBit(resize_waiting, i);
+
+        /* device may have disappeared by now */
+        dixLookupDevice(&dev, i, serverClient, DixWriteAccess);
+        if (!dev)
+            continue;
+
+        /* Need to grow the queue means dropping events. Grow sufficiently so we
+         * don't need to do it often */
+        size = dev->last.num_touches + dev->last.num_touches/2 + 1;
+
+        tmp = realloc(dev->last.touches, size *  sizeof(*dev->last.touches));
+        if (tmp)
+        {
+            int i;
+            dev->last.touches = tmp;
+            for (i = dev->last.num_touches; i < size; i++)
+                TouchInitDDXTouchPoint(dev, &dev->last.touches[i]);
+            dev->last.num_touches = size;
+        }
+
+    }
+    OsReleaseSignals();
+
+    return TRUE;
+}
+
+/**
  * Given the DDX-facing ID (which is _not_ DeviceEvent::detail.touch), find the
  * associated DDXTouchPointInfoRec.
  *
@@ -133,7 +190,16 @@ TouchBeginDDXTouch(DeviceIntPtr dev, uint32_t ddx_id)
         return ti;
     }
 
-    /* If we get here, then we've run out of touches, drop the event */
+    /* If we get here, then we've run out of touches and we need to drop the
+     * event (we're inside the SIGIO handler here) schedule a WorkProc to
+     * grow the queue for us for next time. */
+    ErrorF("%s: not enough space for touch events (max %d touchpoints). "
+           "Dropping this event.\n", dev->name, dev->last.num_touches);
+    if (!BitIsOn(resize_waiting, dev->id)) {
+        SetBit(resize_waiting, dev->id);
+        QueueWorkProc(TouchResizeQueue, serverClient, NULL);
+    }
+
     return NULL;
 }