The accept4() function, compared to accept(), allows setting the new file descriptor atomically close-on-exec and explicitly controlling the non-blocking status on the new socket. (Note that the latter point means that accept() is not equivalent to any form of accept4().) The linuxulator's accept4 implementation leaves a race window where the new file descriptor is not close-on-exec because it calls sys_accept(). This implementation leaves no such race window (by using falloc() flags). The linuxulator could be fixed and simplified by using the new code. Like accept(), accept4() is async-signal-safe, a cancellation point and permitted in capability mode.