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poll.2: Fix discussion of ppoll() timeout argument 

1. Rename ppoll)(_ argument to "timeout_ts" to distinguish it
   from the poll() argument in the text.
2. More accurately describe the poll() call that is equivalent
   to ppoll().

Reported-by: Andi Kleen <andi@firstfloor.org>
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
This commit is contained in:
Michael Kerrisk 2010-06-12 14:15:00 +02:00
parent ed31c5727f
commit b8c599cba0
1 changed files with 16 additions and 14 deletions
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30
man2/poll.2
View File

@ -28,7 +28,7 @@
.\" 2006-07-01, mtk, Added POLLRDHUP + various other wording and
.\" formatting changes.
.\"
.TH POLL 2 2009-09-15 "Linux" "Linux Programmer's Manual"
.TH POLL 2 2010-06-12 "Linux" "Linux Programmer's Manual"
.SH NAME
poll, ppoll \- wait for some event on a file descriptor
.SH SYNOPSIS
@ -41,7 +41,7 @@ poll, ppoll \- wait for some event on a file descriptor
.B #include <poll.h>
.sp
.BI "int ppoll(struct pollfd *" fds ", nfds_t " nfds ", "
.BI " const struct timespec *" timeout ", const sigset_t *" sigmask );
.BI " const struct timespec *" timeout_ts ", const sigset_t *" sigmask );
.fi
.SH DESCRIPTION
.BR poll ()
@ -186,14 +186,13 @@ like
allows an application to safely wait until either a file descriptor
becomes ready or until a signal is caught.
.PP
Other than the difference in the
.I timeout
argument, the following
Other than the difference in the precision of the
timeout argument, the following
.BR ppoll ()
call:
.nf
ready = ppoll(&fds, nfds, timeout, &sigmask);
ready = ppoll(&fds, nfds, timeout_ts, &sigmask);
.fi
is equivalent to
@ -202,7 +201,10 @@ executing the following calls:
.nf
sigset_t origmask;
int timeout;
timeout = (timeout_ts == NULL) ? -1 :
(timeout_ts.tv_sec * 1000 + timeout_ts.tv_nsec / 1000000);
sigprocmask(SIG_SETMASK, &sigmask, &origmask);
ready = poll(&fds, nfds, timeout);
sigprocmask(SIG_SETMASK, &origmask, NULL);
@ -222,12 +224,10 @@ no signal mask manipulation is performed
.BR ppoll ()
differs from
.BR poll ()
only in the precision of the
.I timeout
argument).
only in the precision of the timeout argument).
The
.I timeout
.I timeout_ts
argument specifies an upper limit on the amount of time that
.BR ppoll ()
will block.
@ -243,7 +243,7 @@ struct timespec {
.in
If
.I timeout
.I timeout_ts
is specified as NULL, then
.BR ppoll ()
can block indefinitely.
@ -304,13 +304,15 @@ is Linux-specific.
Some implementations define the nonstandard constant
.B INFTIM
with the value \-1 for use as a
.IR timeout .
.IR timeout
for
.BR poll ()..
This constant is not provided in glibc.
.SS "Linux Notes"
The Linux
.BR ppoll ()
system call modifies its
.I timeout
.I timeout_ts
argument.
However, the glibc wrapper function hides this behavior
by using a local variable for the timeout argument that
@ -318,7 +320,7 @@ is passed to the system call.
Thus, the glibc
.BR ppoll ()
function does not modify its
.I timeout
.I timeout_ts
argument.
.SH BUGS
See the discussion of spurious readiness notifications under the