From: "Michael Kerrisk (man-pages)" <mtk.manpages@gmail.com>
To: Alan Stern <stern@rowland.harvard.edu>,
linux-man@vger.kernel.org,
Kernel development list <linux-kernel@vger.kernel.org>
Cc: mtk.manpages@gmail.com
Subject: Re: Error (?) in man page for ppoll(2)
Date: Mon, 29 Jul 2019 14:07:23 +0200 [thread overview]
Message-ID: <4ce02b01-f174-99a1-ac34-21a2c6414df2@gmail.com> (raw)
In-Reply-To: <Pine.LNX.4.44L0.1907211104350.15063-100000@netrider.rowland.org>
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/
next prev parent reply other threads:[~2019-07-29 12:07 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-07-21 15:32 Error (?) in man page for ppoll(2) Alan Stern
2019-07-29 12:07 ` Michael Kerrisk (man-pages) [this message]
2019-07-29 13:23 ` Alan Stern
2019-07-29 18:56 ` Michael Kerrisk (man-pages)
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=4ce02b01-f174-99a1-ac34-21a2c6414df2@gmail.com \
--to=mtk.manpages@gmail.com \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-man@vger.kernel.org \
--cc=stern@rowland.harvard.edu \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).