Bruno Haible wrote:
TYPE_MAXIMUM (nfds_t) / 2 is good for a quick check against an out-of-bounds
nfd.
POSIX [1] says that nfd is out-of-bounds if it is > getdtablesize().
OK, but getdtablesize returns 'int' so the 'poll' code should compare to INT_MAX
rather than to an expression that would not be appropriate on (admittedly weird)
platforms where nfds_t differs in width from 'int'. Also, that comment is still
confusing. How about the attached?
>From daa5c31db0ba85578ed22cb9f133de2b20279afd Mon Sep 17 00:00:00 2001
From: Paul Eggert <egg...@cs.ucla.edu>
Date: Sat, 22 Apr 2017 18:48:39 -0700
Subject: [PATCH] poll: improve fast check for out-of-range NFD
* lib/poll.c: Do not include intprops.h.
(poll): Compare NFD to INT_MAX, not to TYPE_MAXIMUM (nfds_t) / 2.
---
ChangeLog | 4 ++++
lib/poll.c | 9 ++++-----
2 files changed, 8 insertions(+), 5 deletions(-)
diff --git a/ChangeLog b/ChangeLog
index ad436a7..8a13acc 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,5 +1,9 @@
2017-04-22 Paul Eggert <egg...@cs.ucla.edu>
+ poll: improve fast check for out-of-range NFD
+ * lib/poll.c: Do not include intprops.h.
+ (poll): Compare NFD to INT_MAX, not to TYPE_MAXIMUM (nfds_t) / 2.
+
ftoastr: cite a newer paper
* lib/ftoastr.c (FTOASTR): In comment, cite Andrysco et al. 2016
instead of Loitsch 2010.
diff --git a/lib/poll.c b/lib/poll.c
index 69b3672..078b1ba 100644
--- a/lib/poll.c
+++ b/lib/poll.c
@@ -60,7 +60,6 @@
#include <time.h>
#include "assure.h"
-#include "intprops.h"
#ifndef INFTIM
# define INFTIM (-1)
@@ -336,13 +335,13 @@ poll (struct pollfd *pfd, nfds_t nfd, int timeout)
int maxfd, rc;
nfds_t i;
- if (nfd > TYPE_MAXIMUM (nfds_t) / 2)
+ if (nfd > INT_MAX)
{
errno = EINVAL;
return -1;
}
- /* Don't check directly for NFD too large. Any practical use of a
- too-large NFD is caught by one of the other checks below, and
+ /* Don't check directly for NFD greater than OPEN_MAX. Any practical use
+ of a too-large NFD is caught by one of the other checks below, and
checking directly for getdtablesize is too much of a portability
and/or performance and/or correctness hassle. */
@@ -434,7 +433,7 @@ poll (struct pollfd *pfd, nfds_t nfd, int timeout)
int rc = 0;
nfds_t i;
- if (nfd > TYPE_MAXIMUM (nfds_t) / 2 || timeout < -1)
+ if (nfd > INT_MAX || timeout < -1)
{
errno = EINVAL;
return -1;
--
2.7.4
