I'm aware what sections 2 and 3 are traditionally for. However, you can have "sub-sections", indicated by a letter suffix on the section. E.g. several sections have POSIX specific sub-sections. Compare "man 1 sh" to "man 1p sh", or "man nan" to "man 3p nan".
There's no reason you couldn't have a "k" sub-section (so "2k" and/or "3k"), to document kernel specific things about programming interfaces. There's no reason why you can't have *both* a glibc and Linux kernel specific version for a man-page.