[Ozone] Properly initialize multitouch slot values

ui/events/ozone/evdev/event_device_info.cc

Index: ui/events/ozone/evdev/event_device_info.cc
diff --git a/ui/events/ozone/evdev/event_device_info.cc b/ui/events/ozone/evdev/event_device_info.cc
index 6d75ea9e0c7272cb0726c5052ea41e3e12d9dc19..d9bd17f15f2b4ac72ccf2bf81eb498dbc03ec983 100644
--- a/ui/events/ozone/evdev/event_device_info.cc
+++ b/ui/events/ozone/evdev/event_device_info.cc
@@ -40,6 +40,24 @@ bool GetAbsInfo(int fd, int code, struct input_absinfo* absinfo) {
   return true;
 }
 
+// |request| needs to be the equivalent to:
+// struct input_mt_request_layout {
+//   uint32_t code;
+//   int32_t values[num_slots];
+// };
+//
+// |size| is num_slots + 1 (for code).
+bool GetSlotValues(int fd, int32_t* request, unsigned int size) {
+  if (ioctl(fd,
+            EVIOCGMTSLOTS(sizeof(int32_t) * size),
+            request) < 0) {
+    LOG(ERROR) << "failed EVIOCGMTSLOTS(" << request[0] << ") on fd " << fd;
+    return false;
+  }
+
+  return true;
+}
+
 }  // namespace
 
 EventDeviceInfo::EventDeviceInfo() {
@@ -86,6 +104,20 @@ bool EventDeviceInfo::Initialize(int fd) {
       if (!GetAbsInfo(fd, i, &abs_info_[i]))
         return false;
 
+  int max_num_slots = abs_info_[ABS_MT_SLOT].maximum + 1;
+  // |request| is MT code + slots.
+  int32_t request[max_num_slots + 1];
+  for (unsigned int i = ABS_MT_SLOT + 1; i < ABS_MAX; ++i) {
+    memset(request, 0, sizeof(request));
+    request[0] = i;
+    if (HasAbsEvent(i))
+      if (!GetSlotValues(fd, request, max_num_slots + 1))
+        return false;
+
+    slot_values_[i - ABS_MT_SLOT - 1].assign(
+        request + 1, request + max_num_slots + 1);
+  }
+
   return true;
 }
 
@@ -145,6 +177,14 @@ int32 EventDeviceInfo::GetAbsMaximum(unsigned int code) const {
   return abs_info_[code].maximum;
 }
 
+int32 EventDeviceInfo::GetSlotValue(unsigned int code,
+                                    unsigned int slot) const {
+  const std::vector<int32_t>& slots = GetMtSlotsForCode(code);
+  DCHECK_LE(0u, slot) << slot << " is an invalid slot";
+  DCHECK_LT(slot, slots.size()) << slot << " is an invalid slot";
+  return slots[slot];
+}
+
 bool EventDeviceInfo::HasAbsXY() const {
   if (HasAbsEvent(ABS_X) && HasAbsEvent(ABS_Y))
     return true;
@@ -182,4 +222,12 @@ bool EventDeviceInfo::IsMappedToScreen() const {
   return true;
 }
 
+const std::vector<int32_t>& EventDeviceInfo::GetMtSlotsForCode(int code) const {
+  int index = code - ABS_MT_SLOT - 1;
+  DCHECK_LE(0, index) << code << " is not a valid multi-touch code";
+  DCHECK_LT(index, EVDEV_ABS_MT_COUNT)
+      << code << " is not a valid multi-touch code";
+  return slot_values_[index];
+}
+
 }  // namespace ui