TFD_NONBLOCK
BUILD_BUG_ON(TFD_NONBLOCK != O_NONBLOCK);
#define TFD_SHARED_FCNTL_FLAGS (TFD_CLOEXEC | TFD_NONBLOCK)
timerfd = timerfd_create(CLOCK_MONOTONIC, TFD_CLOEXEC | TFD_NONBLOCK);
int fd = timerfd_create(CLOCK_MONOTONIC, TFD_NONBLOCK);
kvm->timerfd = timerfd_create(CLOCK_MONOTONIC, TFD_NONBLOCK);