ioctl() for dev/video0 gives ENOTTY error

[btarnowski]

Hi all
There is device list in my Linux system

and Im going to set exposure to my camera sensor. I work on C/C++ application.
I can make a picture and set exposure from command this way:

v4l2-ctl --device=/dev/v4l-subdev0 --get-ctrl=exposure
v4l2-ctl -d /dev/v4l-subdev0 --set-ctrl exposure=512 
v4l2-ctl --device=/dev/v4l-subdev0 --get-ctrl=analogue_gain

it uses subdevice concept.

And there is my piece of code, here I work with video0. 
open(...) works ok but I can not set any parameter like exposure.
The v4l2_ioctl(...) returns errno= ENOTTY  (the same errno I get with ioct(...) )

ENOTTY - Not a typewriter

    char *videodevice = (char*)"/dev/video0";
	v4l2_control c;
	int descriptor;

	descriptor = open(videodevice, O_RDWR);
    if(descriptor < 0){
        printf("Error Opening VideoDevice,  errno=%d\n",errno);
    }

 	c.id = V4L2_CID_EXPOSURE_ABSOLUTE;
	c.value = 300;
	if(v4l2_ioctl(descriptor, VIDIOC_S_CTRL, &c) == 0)
		printf("V4L2_CID_EXPOSURE_ABSOLUTE:  Value : %d \n",c.value);
	else
		printf("V4L2_CID_EXPOSURE_ABSOLUTE fail,  errno=%d\n",errno);

What is wrong ? What can I check/debug ?

[btarnowski · Accepted solution]

The control name is wrong. I had to use V4L2_CID_EXPOSURE and  V4L2_CID_ANALOGUE_GAIN as a control id.

Conclusion - do not trust in examples or other working solutions, your specific code can depend on specific details differ than you see in examples

[Bio_TICFSL]

Hello,

Yes you can debug it, but the ENOTY error mean the frmsize structure was left initialize to 0, as side effect, the driver was reporting an invalid frmsize. Size: Stepwise 0x0 - 0x0 with step 0/0 Fix this by replicating the constraints in the raw formats too. This fixes is with software using GSteamer encodebin feature.

 Regards

[btarnowski]

Thank you for your replay,
Do you mean this one structure ?

I found this as your base for answer and it is not so clear for me.
https://lkml.org/lkml/2022/12/23/380

By the way, I can get picture with gstreamer