Re: [PATCH] media: v4l2-core: expose the device after it was registered.

[xinwu]

Hi Sakari,

Thanks for your response.


On 2019å01æ22æ 18:03, Sakari Ailus wrote:
> Hi Xinwu,
>
> On Tue, Jan 22, 2019 at 04:34:44PM +0800, Liu, Xinwu wrote:
> > device_register exposes the device to userspace.
> >
> > Therefore, while the register process is ongoing, the userspace program
> > will fail to open the device (ENODEV will be set to errno currently).
> > The program in userspace must re-open the device to cover this case.
> >
> > It is more reasonable to expose the device after everythings ready.
> >
> > Signed-off-by: Liu, Xinwu <xinwu.liu@xxxxxxxxx>
> > ---
> >   drivers/media/v4l2-core/v4l2-dev.c | 14 ++++++++------
> >   1 file changed, 8 insertions(+), 6 deletions(-)
> >
> > diff --git a/drivers/media/v4l2-core/v4l2-dev.c b/drivers/media/v4l2-core/v4l2-dev.c
> > index d7528f8..01e5cc9 100644
> > --- a/drivers/media/v4l2-core/v4l2-dev.c
> > +++ b/drivers/media/v4l2-core/v4l2-dev.c
> > @@ -993,16 +993,11 @@ int __video_register_device(struct video_device *vdev,
> >   		goto cleanup;
> >   	}
> >   
> > -	/* Part 4: register the device with sysfs */
> > +	/* Part 4: Prepare to register the device */
> >   	vdev->dev.class = &video_class;
> >   	vdev->dev.devt = MKDEV(VIDEO_MAJOR, vdev->minor);
> >   	vdev->dev.parent = vdev->dev_parent;
> >   	dev_set_name(&vdev->dev, "%s%d", name_base, vdev->num);
> > -	ret = device_register(&vdev->dev);
> > -	if (ret < 0) {
> > -		pr_err("%s: device_register failed\n", __func__);
> > -		goto cleanup;
> > -	}
> >   	/* Register the release callback that will be called when the last
> >   	   reference to the device goes away. */
> >   	vdev->dev.release = v4l2_device_release;
> > @@ -1020,6 +1015,13 @@ int __video_register_device(struct video_device *vdev,
> >   	/* Part 6: Activate this minor. The char device can now be used. */
> >   	set_bit(V4L2_FL_REGISTERED, &vdev->flags);
> >   
> > +	/* Part 7: Register the device with sysfs */
> > +	ret = device_register(&vdev->dev);
> > +	if (ret < 0) {
> > +		pr_err("%s: device_register failed\n", __func__);
> > +		goto cleanup;
> The error handling needs to reflect the change as well.

Yes, I think it need to clear the V4L2_FL_REGISTERED also.
> Speaking of which, the error handling appears to be somewhat broken here.
> It should be fixed first before making changes to the registration order.

I guess you mean to call "put_device()" in this error handling.
> The problem the patch addresses is related to another problem: how to tell
> the user space all devices in the media hardware complex have been
> registered successfully. Order generally has been the node first, and only
> then the entity. That suggests the order should probably be:
>
> 1. video_register_media_controller
> 2. set_bit(V4L2_FL_REGISTERED)
> 3. device_register
>
> I wonder what Hans thinks.

Yes, that's my suggestion, thanks for the highlight. I also want to know 
if it's worth to make this change.
> > +	}
> > +
> >   	return 0;
> >   
> >   cleanup: