Man pages matching name cmsg_data in section 3:

CMSG_DATA.3.en	debian 10 / manpages-dev
CMSG_DATA.3.pl	debian 10 / manpages-pl-dev
CMSG_DATA.3.en	debian 11 / manpages-dev
CMSG_DATA.3.pl	debian 11 / manpages-pl-dev
CMSG_DATA.3.en	debian 12 / manpages-dev
CMSG_DATA.3.es	debian 12 / manpages-es-dev
CMSG_DATA.3.fr	debian 12 / manpages-fr-dev
CMSG_DATA.3.ja	debian 12 / manpages-ja-dev