static ssize_t mahimahi_virtual_keys_show(struct kobject *kobj,
			       struct kobj_attribute *attr, char *buf)
{
	if (system_rev > 2) {
		/* center: x: back: 55, menu: 172, home: 298, search 412, y: 835 */
		return sprintf(buf,
			__stringify(EV_KEY) ":" __stringify(KEY_BACK)  ":55:835:90:55"
		   ":" __stringify(EV_KEY) ":" __stringify(KEY_MENU)   ":172:835:125:55"
		   ":" __stringify(EV_KEY) ":" __stringify(KEY_HOME)   ":298:835:115:55"
		   ":" __stringify(EV_KEY) ":" __stringify(KEY_SEARCH) ":412:835:95:55"
		   "\n");
	} else {
		/* center: x: home: 55, menu: 185, back: 305, search 425, y: 835 */
		return sprintf(buf,
			__stringify(EV_KEY) ":" __stringify(KEY_HOME)  ":55:835:70:55"
		   ":" __stringify(EV_KEY) ":" __stringify(KEY_MENU)   ":185:835:100:55"
		   ":" __stringify(EV_KEY) ":" __stringify(KEY_BACK)   ":305:835:70:55"
		   ":" __stringify(EV_KEY) ":" __stringify(KEY_SEARCH) ":425:835:70:55"
		   "\n");
	}
}
 
static struct kobj_attribute mahimahi_virtual_keys_attr = {
	.attr = {
		.name = "virtualkeys.synaptics-rmi-touchscreen",
		.mode = S_IRUGO,
	},
	.show = &mahimahi_virtual_keys_show,
};
 
static struct attribute *mahimahi_properties_attrs[] = {
	&mahimahi_virtual_keys_attr.attr,
	NULL
};
 
static struct attribute_group mahimahi_properties_attr_group = {
	.attrs = mahimahi_properties_attrs,
};
 
struct kobject *properties_kobj;
 
properties_kobj = kobject_create_and_add("board_properties", NULL);
if (properties_kobj)
	ret = sysfs_create_group(properties_kobj,
					 &mahimahi_properties_attr_group);
if (!properties_kobj || ret)
	pr_err("failed to create board_properties\n");

/*这是虚拟按键的类里面包括了VirtualKey所用到的成员变量和按键定位方法*/
    static class VirtualKey {
        int scancode;
        int centerx;
        int centery;
        int width;
        int height;
 
        int hitLeft;
        int hitTop;
        int hitRight;
        int hitBottom;
 
        InputDevice lastDevice;
        int lastKeycode;
 
        boolean checkHit(int x, int y) {
            return (x >= hitLeft && x <= hitRight                     && y >= hitTop && y <= hitBottom);
        }
 
        void computeHitRect(InputDevice dev, int dw, int dh) {
            if (dev == lastDevice) {
                return;
            }
            if (DEBUG_VIRTUAL_KEYS) Log.v(TAG, "computeHitRect for " + scancode
                    + ": dev=" + dev + " absX=" + dev.absX + " absY=" + dev.absY);
 
            lastDevice = dev;
 
            int minx = dev.absX.minValue;
            int maxx = dev.absX.maxValue;
 
            int halfw = width/2;
            int left = centerx - halfw;
            int right = centerx + halfw;
            hitLeft = minx + ((left*maxx-minx)/dw);
            hitRight = minx + ((right*maxx-minx)/dw);
 
            int miny = dev.absY.minValue;
            int maxy = dev.absY.maxValue;
 
            int halfh = height/2;
            int top = centery - halfh;
            int bottom = centery + halfh;
            hitTop = miny + ((top*maxy-miny)/dh);
            hitBottom = miny + ((bottom*maxy-miny)/dh);
        }
    }
/*以下就是与底层接口的函数，如果这个函数和底层接口正常，基本上虚拟按键就能够ok*/
    private void readVirtualKeys(String deviceName) {
        try {
            FileInputStream fis = new FileInputStream(
                    "/sys/board_properties/virtualkeys." + deviceName);
/*这里就是读取kernel给出信息的地方，也就是地层与上层接口的地方，所以整个实现的重点就是这里*/
            InputStreamReader isr = new InputStreamReader(fis);
            BufferedReader br = new BufferedReader(isr, 2048);
            String str = br.readLine();
            if (str != null) {
                String[] it = str.split(":");
                if (DEBUG_VIRTUAL_KEYS) Log.v(TAG, "***** VIRTUAL KEYS: " + it);
                final int N = it.length-6;
                for (int i=0; i<=N; i+=6) {
                    if (!"0x01".equals(it[i])) {
                        Log.w(TAG, "Unknown virtual key type at elem #" + i
                                + ": " + it[i]);
                        continue;
                    }
                    try {
                        VirtualKey sb = new VirtualKey();
                        sb.scancode = Integer.parseInt(it[i+1]);
                        sb.centerx = Integer.parseInt(it[i+2]);
                        sb.centery = Integer.parseInt(it[i+3]);
                        sb.width = Integer.parseInt(it[i+4]);
                        sb.height = Integer.parseInt(it[i+5]);
                        if (DEBUG_VIRTUAL_KEYS) Log.v(TAG, "Virtual key "
                                + sb.scancode + ": center=" + sb.centerx + ","
                                + sb.centery + " size=" + sb.width + "x"
                                + sb.height);
                        mVirtualKeys.add(sb);
                    } catch (NumberFormatException e) {
                        Log.w(TAG, "Bad number at region " + i + " in: "
                                + str, e);
                    }
                }
            }
            br.close();
        } catch (FileNotFoundException e) {
            Log.i(TAG, "No virtual keys found");
        } catch (IOException e) {
            Log.w(TAG, "Error reading virtual keys", e);
        }
    }