svn commit: r292464 - stable/9/lib/libc/resolv

[Eric van Gyzen]

Author: vangyzen
Date: Sat Dec 19 02:49:59 2015
New Revision: 292464
URL: https://svnweb.freebsd.org/changeset/base/292464

Log:
  MFC r289315,r292216
  
  resolver: automatically reload /etc/resolv.conf
  
  On each resolver query, use stat(2) to see if the modification time
  of /etc/resolv.conf has changed.  If so, reload the file and reinitialize
  the resolver library.  However, only call stat(2) if at least two seconds
  have passed since the last call to stat(2), since calling it on every
  query could kill performance.
  
  This new behavior is enabled by default.  Add a "reload-period" option
  to disable it or change the period of the test.
  
  Document this behavior and option in resolv.conf(5).
  
  Polish the man page just enough to appease igor.
  
  Relnotes:       yes
  Sponsored by:   Dell Inc.

Modified:
  stable/9/lib/libc/resolv/res_init.c
  stable/9/lib/libc/resolv/res_private.h
  stable/9/lib/libc/resolv/res_state.c
Directory Properties:
  stable/9/include/   (props changed)
  stable/9/lib/libc/   (props changed)

Modified: stable/9/lib/libc/resolv/res_init.c
==============================================================================
--- stable/9/lib/libc/resolv/res_init.c	Sat Dec 19 02:47:05 2015	(r292463)
+++ stable/9/lib/libc/resolv/res_init.c	Sat Dec 19 02:49:59 2015	(r292464)
@@ -78,6 +78,7 @@ __FBSDID("$FreeBSD$");
 #include <sys/types.h>
 #include <sys/param.h>
 #include <sys/socket.h>
+#include <sys/stat.h>
 #include <sys/time.h>
 
 #include <netinet/in.h>
@@ -238,6 +239,7 @@ __res_vinit(res_state statp, int preinit
 		statp->_u._ext.ext->nsaddrs[0].sin = statp->nsaddr;
 		strcpy(statp->_u._ext.ext->nsuffix, "ip6.arpa");
 		strcpy(statp->_u._ext.ext->nsuffix2, "ip6.int");
+		statp->_u._ext.ext->reload_period = 2;
 	} else {
 		/*
 		 * Historically res_init() rarely, if at all, failed.
@@ -323,6 +325,18 @@ __res_vinit(res_state statp, int preinit
 
 	nserv = 0;
 	if ((fp = fopen(_PATH_RESCONF, "r")) != NULL) {
+	    struct stat sb;
+	    struct timespec now;
+
+	    if (statp->_u._ext.ext != NULL) {
+		if (_fstat(fileno(fp), &sb) == 0) {
+		    statp->_u._ext.ext->conf_mtim = sb.st_mtim;
+		    if (clock_gettime(CLOCK_MONOTONIC_FAST, &now) == 0) {
+			statp->_u._ext.ext->conf_stat = now.tv_sec;
+		    }
+		}
+	    }
+
 	    /* read the config file */
 	    while (fgets(buf, sizeof(buf), fp) != NULL) {
 		/* skip comments */
@@ -583,9 +597,7 @@ res_setoptions(res_state statp, const ch
 {
 	const char *cp = options;
 	int i;
-#ifndef _LIBC
 	struct __res_state_ext *ext = statp->_u._ext.ext;
-#endif
 
 #ifdef DEBUG
 	if (statp->options & RES_DEBUG)
@@ -668,6 +680,12 @@ res_setoptions(res_state statp, const ch
 		} else if (!strncmp(cp, "no-check-names",
 				    sizeof("no-check-names") - 1)) {
 			statp->options |= RES_NOCHECKNAME;
+		} else if (!strncmp(cp, "reload-period:",
+				    sizeof("reload-period:") - 1)) {
+			if (ext != NULL) {
+				ext->reload_period = (u_short)
+				    atoi(cp + sizeof("reload-period:") - 1);
+			}
 		}
 #ifdef RES_USE_EDNS0
 		else if (!strncmp(cp, "edns0", sizeof("edns0") - 1)) {

Modified: stable/9/lib/libc/resolv/res_private.h
==============================================================================
--- stable/9/lib/libc/resolv/res_private.h	Sat Dec 19 02:47:05 2015	(r292463)
+++ stable/9/lib/libc/resolv/res_private.h	Sat Dec 19 02:49:59 2015	(r292464)
@@ -1,3 +1,5 @@
+/* $FreeBSD$ */
+
 #ifndef res_private_h
 #define res_private_h
 
@@ -12,6 +14,9 @@ struct __res_state_ext {
 	} sort_list[MAXRESOLVSORT];
 	char nsuffix[64];
 	char nsuffix2[64];
+	struct timespec	conf_mtim;	/* mod time of loaded resolv.conf */
+	time_t		conf_stat;	/* time of last stat(resolv.conf) */
+	u_short	reload_period;		/* seconds between stat(resolv.conf) */
 };
 
 extern int

Modified: stable/9/lib/libc/resolv/res_state.c
==============================================================================
--- stable/9/lib/libc/resolv/res_state.c	Sat Dec 19 02:47:05 2015	(r292463)
+++ stable/9/lib/libc/resolv/res_state.c	Sat Dec 19 02:49:59 2015	(r292464)
@@ -26,6 +26,8 @@
  */
 
 #include <sys/types.h>
+#include <sys/stat.h>
+#include <sys/time.h>
 #include <netinet/in.h>
 #include <arpa/nameser.h>
 #include <resolv.h>
@@ -35,6 +37,8 @@
 #include "reentrant.h"
 #include "un-namespace.h"
 
+#include "res_private.h"
+
 #undef _res
 
 struct __res_state _res;
@@ -59,13 +63,44 @@ res_keycreate(void)
 	res_thr_keycreated = thr_keycreate(&res_key, free_res) == 0;
 }
 
+static res_state
+res_check_reload(res_state statp)
+{
+	struct timespec now;
+	struct stat sb;
+	struct __res_state_ext *ext;
+
+	if ((statp->options & RES_INIT) == 0) {
+		return (statp);
+	}
+
+	ext = statp->_u._ext.ext;
+	if (ext == NULL || ext->reload_period == 0) {
+		return (statp);
+	}
+
+	if (clock_gettime(CLOCK_MONOTONIC_FAST, &now) != 0 ||
+	    (now.tv_sec - ext->conf_stat) < ext->reload_period) {
+		return (statp);
+	}
+
+	ext->conf_stat = now.tv_sec;
+	if (stat(_PATH_RESCONF, &sb) == 0 &&
+	    (sb.st_mtim.tv_sec  != ext->conf_mtim.tv_sec ||
+	     sb.st_mtim.tv_nsec != ext->conf_mtim.tv_nsec)) {
+		statp->options &= ~RES_INIT;
+	}
+
+	return (statp);
+}
+
 res_state
 __res_state(void)
 {
 	res_state statp;
 
 	if (thr_main() != 0)
-		return (&_res);
+		return res_check_reload(&_res);
 
 	if (thr_once(&res_init_once, res_keycreate) != 0 ||
 	    !res_thr_keycreated)
@@ -73,7 +108,7 @@ __res_state(void)
 
 	statp = thr_getspecific(res_key);
 	if (statp != NULL)
-		return (statp);
+		return res_check_reload(statp);
 	statp = calloc(1, sizeof(*statp));
 	if (statp == NULL)
 		return (&_res);