создать файловый дескриптор для обработки ошибок страниц в пользовательском пространстве (create a file descriptor for handling page faults in user space)
Ошибки (Error)
EINVAL An unsupported value was specified in flags.
EMFILE The per-process limit on the number of open file
descriptors has been reached
ENFILE The system-wide limit on the total number of open files
has been reached.
ENOMEM Insufficient kernel memory was available.
EPERM (since Linux 5.2)
The caller is not privileged (does not have the
CAP_SYS_PTRACE capability in the initial user namespace),
and /proc/sys/vm/unprivileged_userfaultfd has the value 0.