缺少 v4l2、linux 与 uapi/linux 中的包含

Question

I'm learning the v4l2 API for configuring video devices through v4l2-ctl. The code samples from ages ago are really out of date and some of the defines don't work anymore. There is a new method of requesting everything for the API from the kerhel which is shown in v4l2-utils. I'm trying to incorporate some of the code from v4l2-utils into my code. However, I'm getting an error from the compiler:

camera.hpp:1038:8: error: 'struct v4l2_ext_controls' has no member named 'which'

ctrls.which = V4L2_CTRL_ID2WHICH(qctrl.id);

And:

camera.hpp:1038:43: error: 'V4L2_CTRL_ID2WHICH' was not declared in this scope

ctrls.which = V4L2_CTRL_ID2WHICH(qctrl.id);

The field and define are in a file located in the linux source tree: /usr/src/linux-4.6.3-gentoo/include/uapi/linux/videodev2.h, but that file is not included when I specify:

#include <linux/videodev2.h>

What is the voodoo to get the compiler to include the correct file?

I've been studying the v4l2-utils source but can't figure it out.

Thanks much.

Answer 1

The file located in /usr/include was out of date. I had the headers installed for kernel 4.3 and needed the ones from a later version. The solution for my gentoo install was to add a keyword for sys-kernel/linux-headers and install the latest headers (4.7).

It turns out that the UAPI file becomes the headers when installed into /usr/include. I could probably have accomplished this with make headers_install in my /usr/src/linux directory as well, but I'm not sure whether that is more "correct" than installing the linux-headers ebuild. I worry about conflicts.

Hope this helps someone else...