media: v4l2-dev: Add v4l2_device_register_ro_subdev_node()

Add to the V4L2 core a function to register device nodes for video
subdevices in read-only mode.

Registering a device node in read-only mode is useful to expose to
userspace the current sub-device configuration, without allowing
application to change it by using the V4L2 subdevice ioctls.

Acked-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Jacopo Mondi <jacopo@jmondi.org>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>

drivers/media/v4l2-core/v4l2-device.c

@@ -186,7 +186,8 @@ static void v4l2_device_release_subdev_node(struct video_device *vdev)
 	kfree(vdev);
 }
 
-int v4l2_device_register_subdev_nodes(struct v4l2_device *v4l2_dev)
+int __v4l2_device_register_subdev_nodes(struct v4l2_device *v4l2_dev,
+					bool read_only)
 {
 	struct video_device *vdev;
 	struct v4l2_subdev *sd;
@@ -215,6 +216,8 @@ int v4l2_device_register_subdev_nodes(struct v4l2_device *v4l2_dev)
 		vdev->fops = &v4l2_subdev_fops;
 		vdev->release = v4l2_device_release_subdev_node;
 		vdev->ctrl_handler = sd->ctrl_handler;
+		if (read_only)
+			set_bit(V4L2_FL_SUBDEV_RO_DEVNODE, &vdev->flags);
 		err = __video_register_device(vdev, VFL_TYPE_SUBDEV, -1, 1,
 					      sd->owner);
 		if (err < 0) {
@@ -252,7 +255,7 @@ int v4l2_device_register_subdev_nodes(struct v4l2_device *v4l2_dev)
 
 	return err;
 }
-EXPORT_SYMBOL_GPL(v4l2_device_register_subdev_nodes);
+EXPORT_SYMBOL_GPL(__v4l2_device_register_subdev_nodes);
 
 void v4l2_device_unregister_subdev(struct v4l2_subdev *sd)
 {

drivers/media/v4l2-core/v4l2-subdev.c

@@ -331,6 +331,7 @@ static long subdev_do_ioctl(struct file *file, unsigned int cmd, void *arg)
 	struct v4l2_fh *vfh = file->private_data;
 #if defined(CONFIG_VIDEO_V4L2_SUBDEV_API)
 	struct v4l2_subdev_fh *subdev_fh = to_v4l2_subdev_fh(vfh);
+	bool ro_subdev = test_bit(V4L2_FL_SUBDEV_RO_DEVNODE, &vdev->flags);
 #endif
 	int rval;
 
@@ -477,6 +478,9 @@ static long subdev_do_ioctl(struct file *file, unsigned int cmd, void *arg)
 	case VIDIOC_SUBDEV_S_FMT: {
 		struct v4l2_subdev_format *format = arg;
 
+		if (format->which != V4L2_SUBDEV_FORMAT_TRY && ro_subdev)
+			return -EPERM;
+
 		memset(format->reserved, 0, sizeof(format->reserved));
 		memset(format->format.reserved, 0, sizeof(format->format.reserved));
 		return v4l2_subdev_call(sd, pad, set_fmt, subdev_fh->pad, format);
@@ -504,6 +508,9 @@ static long subdev_do_ioctl(struct file *file, unsigned int cmd, void *arg)
 		struct v4l2_subdev_crop *crop = arg;
 		struct v4l2_subdev_selection sel;
 
+		if (crop->which != V4L2_SUBDEV_FORMAT_TRY && ro_subdev)
+			return -EPERM;
+
 		memset(crop->reserved, 0, sizeof(crop->reserved));
 		memset(&sel, 0, sizeof(sel));
 		sel.which = crop->which;
@@ -545,6 +552,9 @@ static long subdev_do_ioctl(struct file *file, unsigned int cmd, void *arg)
 	case VIDIOC_SUBDEV_S_FRAME_INTERVAL: {
 		struct v4l2_subdev_frame_interval *fi = arg;
 
+		if (ro_subdev)
+			return -EPERM;
+
 		memset(fi->reserved, 0, sizeof(fi->reserved));
 		return v4l2_subdev_call(sd, video, s_frame_interval, arg);
 	}
@@ -568,6 +578,9 @@ static long subdev_do_ioctl(struct file *file, unsigned int cmd, void *arg)
 	case VIDIOC_SUBDEV_S_SELECTION: {
 		struct v4l2_subdev_selection *sel = arg;
 
+		if (sel->which != V4L2_SUBDEV_FORMAT_TRY && ro_subdev)
+			return -EPERM;
+
 		memset(sel->reserved, 0, sizeof(sel->reserved));
 		return v4l2_subdev_call(
 			sd, pad, set_selection, subdev_fh->pad, sel);
@@ -604,6 +617,9 @@ static long subdev_do_ioctl(struct file *file, unsigned int cmd, void *arg)
 		return v4l2_subdev_call(sd, video, g_dv_timings, arg);
 
 	case VIDIOC_SUBDEV_S_DV_TIMINGS:
+		if (ro_subdev)
+			return -EPERM;
+
 		return v4l2_subdev_call(sd, video, s_dv_timings, arg);
 
 	case VIDIOC_SUBDEV_G_STD:
@@ -612,6 +628,9 @@ static long subdev_do_ioctl(struct file *file, unsigned int cmd, void *arg)
 	case VIDIOC_SUBDEV_S_STD: {
 		v4l2_std_id *std = arg;
 
+		if (ro_subdev)
+			return -EPERM;
+
 		return v4l2_subdev_call(sd, video, s_std, *std);
 	}
 

include/media/v4l2-dev.h

@@ -82,11 +82,18 @@ struct v4l2_ctrl_handler;
  *	but the old crop API will still work as expected in order to preserve
  *	backwards compatibility.
  *	Never set this flag for new drivers.
+ * @V4L2_FL_SUBDEV_RO_DEVNODE:
+ *	indicates that the video device node is registered in read-only mode.
+ *	The flag only applies to device nodes registered for sub-devices, it is
+ *	set by the core when the sub-devices device nodes are registered with
+ *	v4l2_device_register_ro_subdev_nodes() and used by the sub-device ioctl
+ *	handler to restrict access to some ioctl calls.
  */
 enum v4l2_video_device_flags {
 	V4L2_FL_REGISTERED		= 0,
 	V4L2_FL_USES_V4L2_FH		= 1,
 	V4L2_FL_QUIRK_INVERTED_CROP	= 2,
+	V4L2_FL_SUBDEV_RO_DEVNODE	= 3,
 };
 
 /* Priority helper functions */

include/media/v4l2-device.h

@@ -174,14 +174,56 @@ int __must_check v4l2_device_register_subdev(struct v4l2_device *v4l2_dev,
 void v4l2_device_unregister_subdev(struct v4l2_subdev *sd);
 
 /**
- * v4l2_device_register_subdev_nodes - Registers device nodes for all subdevs
- *	of the v4l2 device that are marked with
- *	the %V4L2_SUBDEV_FL_HAS_DEVNODE flag.
+ * __v4l2_device_register_ro_subdev_nodes - Registers device nodes for
+ *      all subdevs of the v4l2 device that are marked with the
+ *      %V4L2_SUBDEV_FL_HAS_DEVNODE flag.
  *
  * @v4l2_dev: pointer to struct v4l2_device
+ * @read_only: subdevices read-only flag. True to register the subdevices
+ *	device nodes in read-only mode, false to allow full access to the
+ *	subdevice userspace API.
  */
 int __must_check
-v4l2_device_register_subdev_nodes(struct v4l2_device *v4l2_dev);
+__v4l2_device_register_subdev_nodes(struct v4l2_device *v4l2_dev,
+				    bool read_only);
+
+/**
+ * v4l2_device_register_subdev_nodes - Registers subdevices device nodes with
+ *	unrestricted access to the subdevice userspace operations
+ *
+ * Internally calls __v4l2_device_register_subdev_nodes(). See its documentation
+ * for more details.
+ *
+ * @v4l2_dev: pointer to struct v4l2_device
+ */
+static inline int __must_check
+v4l2_device_register_subdev_nodes(struct v4l2_device *v4l2_dev)
+{
+#if defined(CONFIG_VIDEO_V4L2_SUBDEV_API)
+	return __v4l2_device_register_subdev_nodes(v4l2_dev, false);
+#else
+	return 0;
+#endif
+}
+
+/**
+ * v4l2_device_register_ro_subdev_nodes - Registers subdevices device nodes
+ *	in read-only mode
+ *
+ * Internally calls __v4l2_device_register_subdev_nodes(). See its documentation
+ * for more details.
+ *
+ * @v4l2_dev: pointer to struct v4l2_device
+ */
+static inline int __must_check
+v4l2_device_register_ro_subdev_nodes(struct v4l2_device *v4l2_dev)
+{
+#if defined(CONFIG_VIDEO_V4L2_SUBDEV_API)
+	return __v4l2_device_register_subdev_nodes(v4l2_dev, true);
+#else
+	return 0;
+#endif
+}
 
 /**
  * v4l2_subdev_notify - Sends a notification to v4l2_device.