From 8d113f4aeccc18d4c473855fdd4c865297decdd9 Mon Sep 17 00:00:00 2001
From: Edward Tomasz Napierala <trasz@FreeBSD.org>
Date: Sat, 10 Nov 2018 23:07:46 +0000
Subject: [PATCH] Don't call stat(2) on nsswitch.conf(5) every time
 nsdispatch(3) and dependent functions (eg getpwname(3)) get called. This can
 improve performance of binaries that perform a lot of name lookups, such as
 gssd(8). It also matches documented behaviour of Linux and Solaris.

The old code is left in place, should anyone need it, guarded
by #ifdef NS_REREAD_CONF.

Reviewed by:	imp, bcr
MFC after:	2 weeks
Relnotes:	yes
Sponsored by:	DARPA, AFRL
Differential Revision:	https://reviews.freebsd.org/D17934
---
 lib/libc/net/nsdispatch.c      | 11 +++++++++++
 share/man/man5/nsswitch.conf.5 |  8 +++++++-
 2 files changed, 18 insertions(+), 1 deletion(-)

diff --git a/lib/libc/net/nsdispatch.c b/lib/libc/net/nsdispatch.c
index b9533bd1ca4..b0f80d079b0 100644
--- a/lib/libc/net/nsdispatch.c
+++ b/lib/libc/net/nsdispatch.c
@@ -335,6 +335,7 @@ static int
 nss_configure(void)
 {
 	static time_t	 confmod;
+	static int	 already_initialized = 0;
 	struct stat	 statbuf;
 	int		 result, isthreaded;
 	const char	*path;
@@ -352,6 +353,16 @@ nss_configure(void)
 	if (path == NULL)
 #endif
 		path = _PATH_NS_CONF;
+#ifndef NS_REREAD_CONF
+	/*
+	 * Define NS_REREAD_CONF to have nsswitch notice changes
+	 * to nsswitch.conf(5) during runtime.  This involves calling
+	 * stat(2) every time, which can result in performance hit.
+	 */
+	if (already_initialized)
+		return (0);
+	already_initialized = 1;
+#endif /* NS_REREAD_CONF */
 	if (stat(path, &statbuf) != 0)
 		return (0);
 	if (statbuf.st_mtime <= confmod)
diff --git a/share/man/man5/nsswitch.conf.5 b/share/man/man5/nsswitch.conf.5
index ec5d94c313f..4ebb4a38356 100644
--- a/share/man/man5/nsswitch.conf.5
+++ b/share/man/man5/nsswitch.conf.5
@@ -33,7 +33,7 @@
 .\"
 .\" $FreeBSD$
 .\"
-.Dd June 6, 2016
+.Dd November 10, 2018
 .Dt NSSWITCH.CONF 5
 .Os
 .Sh NAME
@@ -340,6 +340,12 @@ sets a policy of "if the user is notfound in nis, do not try files."
 This treats nis as the authoritative source of information, except
 when the server is down.
 .Sh NOTES
+The
+.Nm
+file is parsed by each program only once.
+Subsequent changes will not be applied until the program
+is restarted.
+.Pp
 If system got compiled with
 .Va WITHOUT_NIS
 you have to remove