Hello Alan, On 7/21/19 5:32 PM, Alan Stern wrote: > 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. Thanks for the report, and the text change suggestions. I've applied the patch below. Thanks, Michael diff --git a/man2/poll.2 b/man2/poll.2 index 0b023e0a5..3eacb88b7 100644 --- a/man2/poll.2 +++ b/man2/poll.2 @@ -271,7 +271,7 @@ ready = ppoll(&fds, nfds, tmo_p, &sigmask); .EE .in .PP -is equivalent to +is nearly equivalent to .I atomically executing the following calls: .PP @@ -288,6 +288,17 @@ pthread_sigmask(SIG_SETMASK, &origmask, NULL); .EE .in .PP +The above code segment is described as +.I nearly +equivalent because whereas a negative +.I timeout +value for +.BR poll () +is interpreted as an infinite timeout, a negative value expressed in +.IR *tmo_p +results in an error from +.BR ppoll (). +.PP See the description of .BR pselect (2) for an explanation of why @@ -354,6 +365,12 @@ value exceeds the .B RLIMIT_NOFILE value. .TP +.B EINVAL +.RB ( ppoll ()) +The timeout value expressed in +.IR *ip +is invalid (nragtive). +.TP .B ENOMEM There was no space to allocate file descriptor tables. .SH VERSIONS -- Michael Kerrisk Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/ Linux/UNIX System Programming Training: http://man7.org/training/
