uvc: Forward compat ioctls to their handlers directly

commit a44323e2 upstream.

The current code goes through a lot of indirection just to call a
known handler.  Simplify it: just call the handlers directly.
Signed-off-by: Andy Lutomirski <luto@kernel.org>
[bwh: Backported to 3.16: old code forwarded to uvc_v4l2_ioctl()]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

drivers/media/usb/uvc/uvc_v4l2.c

@@ -1279,47 +1279,44 @@ static int uvc_v4l2_put_xu_query(const struct uvc_xu_control_query *kp,
 static long uvc_v4l2_compat_ioctl32(struct file *file,
 		     unsigned int cmd, unsigned long arg)
 {
+	struct uvc_fh *handle = file->private_data;
 	union {
 		struct uvc_xu_control_mapping xmap;
 		struct uvc_xu_control_query xqry;
 	} karg;
 	void __user *up = compat_ptr(arg);
-	mm_segment_t old_fs;
 	long ret;
 
 	switch (cmd) {
 	case UVCIOC_CTRL_MAP32:
-		cmd = UVCIOC_CTRL_MAP;
 		ret = uvc_v4l2_get_xu_mapping(&karg.xmap, up);
+		if (ret)
+			return ret;
+		ret = uvc_ioctl_ctrl_map(handle->chain, &karg.xmap);
+		if (ret)
+			return ret;
+		ret = uvc_v4l2_put_xu_mapping(&karg.xmap, up);
+		if (ret)
+			return ret;
+
 		break;
 
 	case UVCIOC_CTRL_QUERY32:
-		cmd = UVCIOC_CTRL_QUERY;
 		ret = uvc_v4l2_get_xu_query(&karg.xqry, up);
+		if (ret)
+			return ret;
+		ret = uvc_xu_ctrl_query(handle->chain, &karg.xqry);
+		if (ret)
+			return ret;
+		ret = uvc_v4l2_put_xu_query(&karg.xqry, up);
+		if (ret)
+			return ret;
 		break;
 
 	default:
 		return -ENOIOCTLCMD;
 	}
 
-	old_fs = get_fs();
-	set_fs(KERNEL_DS);
-	ret = uvc_v4l2_ioctl(file, cmd, (unsigned long)&karg);
-	set_fs(old_fs);
-
-	if (ret < 0)
-		return ret;
-
-	switch (cmd) {
-	case UVCIOC_CTRL_MAP:
-		ret = uvc_v4l2_put_xu_mapping(&karg.xmap, up);
-		break;
-
-	case UVCIOC_CTRL_QUERY:
-		ret = uvc_v4l2_put_xu_query(&karg.xqry, up);
-		break;
-	}
-
 	return ret;
 }
 #endif