Re: Add dprintk calls for control validation in v4l2-ctrls.c?

[Hans Verkuil <hverkuil@xs4all.nl>]

Hi Daniel,

On 27/04/2021 02:17, Daniel Almeida wrote:
> Hi Hans, Ezequiel & all.
> 
> I find it a bit hard to debug my own code when it invariably sneaks in a 
> bad control value with the VIDIOC_S_EXT_CTRLS ioctl.
> 
> 
> I feel that it would be tremendously beneficial to encourage the use of 
> dprintk calls in v4l2-ctrls.c to inform the user about what pieces of 
> data were actually rejected in the validation functions.

Makes sense!

> 
> #define dprintk(vdev, fmt, arg...) do {					\
> 	if (!WARN_ON(!(vdev)) && ((vdev)->dev_debug & V4L2_DEV_DEBUG_CTRL)) \
> 		printk(KERN_DEBUG pr_fmt("%s: %s: " fmt),		\
> 		       __func__, video_device_node_name(vdev), ##arg);	
> 
> 
> Unfortunately the dprintk macro above takes a pointer to struct 
> video_device as argument. This is not available in the places I want to 
> actually place the calls, as far as I could tell.
> 
> E.g. here:
> 
> static int std_validate_compound(const struct v4l2_ctrl *ctrl, u32 idx,
> 				 union v4l2_ctrl_ptr ptr)
> 
> I'd like to make the changes to make this possible, if any, or be 
> pointed at another solution if there is one - such as calling pr_err 
> directly or something along these lines - please.

I have no problem with changing the prototypes to pass a vdev pointer
along. The validate_new function is the starting point for that.

However, keep in mind that it can also be called from a driver via e.g.
__v4l2_ctrl_s_ctrl(), in which case there is no video_device, so the
debug code has to be able to handle the case where vdev == NULL, and
not do a WARN_ON in that case.

I would postpone working on this though. Early in the next cycle I want
to merge a large refactor patch found here:

https://git.linuxtv.org/hverkuil/media_tree.git/log/?h=ctrl-refactor

where v4l2-ctrls.c is split up in several pieces. I suggest you wait until
that's merged before making patches for the control framework.

Regards,

	Hans

> 
> Kindly advise?
> 
> -- thanks
> -- Daniel
>