[src/trunk]: src/sys/kern Add slop of 1000 and explain why.

[christos <christos%NetBSD.org@localhost>]

details:   https://anonhg.NetBSD.org/src/rev/d020fd97adc8
branches:  trunk
changeset: 451145:d020fd97adc8
user:      christos <christos%NetBSD.org@localhost>
date:      Wed May 08 00:55:18 2019 +0000

description:
Add slop of 1000 and explain why.

diffstat:

 sys/kern/sys_select.c |  12 ++++++++----
 1 files changed, 8 insertions(+), 4 deletions(-)

diffs (40 lines):

diff -r a15e54026aeb -r d020fd97adc8 sys/kern/sys_select.c
--- a/sys/kern/sys_select.c     Tue May 07 22:00:10 2019 +0000
+++ b/sys/kern/sys_select.c     Wed May 08 00:55:18 2019 +0000
@@ -1,4 +1,4 @@
-/*     $NetBSD: sys_select.c,v 1.44 2019/05/07 20:10:21 christos Exp $ */
+/*     $NetBSD: sys_select.c,v 1.45 2019/05/08 00:55:18 christos Exp $ */
 
 /*-
  * Copyright (c) 2007, 2008, 2009, 2010 The NetBSD Foundation, Inc.
@@ -84,7 +84,7 @@
  */
 
 #include <sys/cdefs.h>
-__KERNEL_RCSID(0, "$NetBSD: sys_select.c,v 1.44 2019/05/07 20:10:21 christos Exp $");
+__KERNEL_RCSID(0, "$NetBSD: sys_select.c,v 1.45 2019/05/08 00:55:18 christos Exp $");
 
 #include <sys/param.h>
 #include <sys/systm.h>
@@ -488,7 +488,7 @@
        int             error;
        size_t          ni;
 
-       if (nfds > curlwp->l_proc->p_rlimit[RLIMIT_NOFILE].rlim_max) {
+       if (nfds > curlwp->l_proc->p_rlimit[RLIMIT_NOFILE].rlim_max + 1000) {
                /*
                 * Prevent userland from causing over-allocation.
                 * Raising the default limit too high can still cause
@@ -505,7 +505,11 @@
                 *
                 * Using the max limit equivalent to sysctl
                 * kern.maxfiles is the moral equivalent of OPEN_MAX
-                * as specified by POSIX
+                * as specified by POSIX.
+                *
+                * We add a slop of 1000 in case the resource limit was
+                * changed after opening descriptors or the same descriptor
+                * was specified more than once.
                 */
                return EINVAL;
        }