SFD_NONBLOCK
BUILD_BUG_ON(SFD_NONBLOCK != O_NONBLOCK);
if (flags & ~(SFD_CLOEXEC | SFD_NONBLOCK))
sample_sig_fd = signalfd(-1, &st, SFD_CLOEXEC | SFD_NONBLOCK);
daemon->signal_fd = signalfd(-1, &mask, SFD_NONBLOCK|SFD_CLOEXEC);
self->signal_fd = signalfd(-1, &mask, SFD_NONBLOCK);