Implement eventfd system call.

[dchagin]

Summary

In collaboration with: Jilles Tjoelker

[trasz]

A general note: have you considered turning it into a FreeBSD syscall, living in eg sys/kern/kern_eventfd.c, with a Linux wrapper around it? This - and some other Linux-specific syscalls - could end up making porting software easier.

[trasz]

sys/compat/linux/linux_event.c

523

Use UMA with its own zone instead of malloc with M_EPOLL? You could then move mtx_init/mtx_destroy into ctor/dtor.

[dchagin]

In D1094#3, @trasz wrote:

A general note: have you considered turning it into a FreeBSD syscall, living in eg sys/kern/kern_eventfd.c, with a Linux wrapper around it? This - and some other Linux-specific syscalls - could end up making porting software easier.

ugh, I can, it seems to me that we need discuss it in public, some people ask me to make native epoll also.

[dchagin]

After D2172 rewrite as a tiny wrapper.

[dchagin]

Full Linuxulator version commited.