With epoll-shim 0.0.20210418 the warning in x11/foot should hopefully be fixed.

Whoops, the x11/foot failure actually is a bug in epoll-shim. I messed up the "fcntl" dispatch logic a bit, is actually was intended to compile warning free on all C99 conforming compilers. A fix for epoll-shim is incoming.

I wrote/compiled a bunch of eventfd ATF tests as part of epoll-shim (https://github.com/jiixyj/epoll-shim/blob/master/test/eventfd-ctx-test.c, https://github.com/jiixyj/epoll-shim/blob/master/test/tst-eventfd.c). I would be happy to clean them up further and contribute them to the FreeBSD test suite in case a native eventfd gets accepted.

There also was https://reviews.freebsd.org/D2172 but I'm not sure how much of that is relevant anymore.

I've uploaded a new version of the patch:

Thank you for the review! I've incorporated your comments and updated the diff.

... so it's worth trying to enable it by default again as support of this device is definitely changed since 2013.

This was tried some years ago, but then reverted as the probing was deemed too intrusive (see r255152 and r255210). I don't know if something changed in the meantime.

I've added some inline comments about Linux device names, IDs and properties.
Here is a patch that I'm using on top of this series right now: