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>

2 files changed, 24 insertions, 2 deletions

diff --git a/drivers/media/v4l2-core/v4l2-device.c b/drivers/media/v4l2-core/v4l2-device.c
index c69941214bb2..de4287251a89 100644
--- a/drivers/media/v4l2-core/v4l2-device.c
+++ b/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 @@ clean_up:
 
 	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)
 {
diff --git a/drivers/media/v4l2-core/v4l2-subdev.c b/drivers/media/v4l2-core/v4l2-subdev.c
index a376b351135f..1dc263c2ca0a 100644
--- a/drivers/media/v4l2-core/v4l2-subdev.c
+++ b/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);
 	}