средство уведомления о событиях ввода / вывода (I/O event notification facility)
Примечание (Note)
The set of file descriptors that is being monitored via an epoll
file descriptor can be viewed via the entry for the epoll file
descriptor in the process's /proc/[pid]/fdinfo directory. See
proc(5) for further details.
The kcmp(2) KCMP_EPOLL_TFD operation can be used to test whether
a file descriptor is present in an epoll instance.
