Hi, although being used in quite a number of init scripts I didn't find any documentation about the mountinfo/fstabinfo utilities. Although one can find some information about both tools by calling them directly I think they deserve to be mentioned in some man page.
Looking this over, it seems that the best place for this documentation will be the BUILTINS section of the openrc-run man page.
https://github.com/openrc/openrc/commit/c2d256ba Documentation has been added to the openrc-run man page. This will be part of openrc-0.29.