/dev/null on FreeBSD: invalid fd

[segoon]

First, thanks for such a good library. I tried to run unit tests of userver (https://github.com/userver-framework/userver) on FreeBSD 13.1 and got an assert from libev: libev: kqueue found invalid fd. I think it is a problem of libev:

1. it is not EBADF, it is ENODEV (device doesn't support operation0, /dev/null doesn't support read/write I suppose. One should not assert on that. It looks odd to get "ok, you can read from fd" on Linux and assert on FreeBSD for /dev/null read polls.
2. the error message is cryptic, it is "operation not supported" and not "invalid fd".