Messages in this thread | | | Date | Sun, 21 Jul 2019 11:32:16 -0400 (EDT) | From | Alan Stern <> | Subject | Error (?) in man page for ppoll(2) |
| |
Here are two extracts from the man page for ppoll(2) (from the man-pages 4.16 package; the 5.01 version is the same):
Specifying a negative value in timeout means an infinite timeout.
Other than the difference in the precision of the timeout argument, the following ppoll() call:
ready = ppoll(&fds, nfds, tmo_p, &sigmask);
is equivalent to atomically executing the following calls:
sigset_t origmask; int timeout;
timeout = (tmo_p == NULL) ? -1 : (tmo_p->tv_sec * 1000 + tmo_p->tv_nsec / 1000000); pthread_sigmask(SIG_SETMASK, &sigmask, &origmask); ready = poll(&fds, nfds, timeout); pthread_sigmask(SIG_SETMASK, &origmask, NULL);
But if tmo_p->tv_sec is negative, the ppoll() call is not equivalent to the corresponding poll() call. The kernel rejects negative values of tv_sec with an EINVAL error; it does not interpret the value as meaning an infinite timeout.
(Yes, the kernel interprets tmo_p == NULL as an infinite timeout, but the man page is still wrong for the case tmo_p->tv_sec < 0.)
Suggested fix: Following the end of the second extract above, add:
except that negative time values in tmo_p are not interpreted as an infinite timeout.
Also, in the ERRORS section, change the text for EINVAL to:
EINVAL The nfds value exceeds the RLIMIT_NOFILE value or *tmo_p contains an invalid (negative) time value.
Alan Stern
| |