[master] Add option to suppress the use of fsync when writing lease files

The option is dont-use-async <flag> and it defaults to disabled.

RELNOTES

@@ -89,6 +89,13 @@ work on other platforms. Please report any problems and suggested fixes to
   key for security reasons.
   [ISC-Bugs 30461]
 
+- Add a configuration option to the server to suppress using fsync().
+  Enabling this option will mean that fsync() is never called.  This
+  may provide better performance but there is also a risk that a lease
+  will not be properly written to the disk after it has been issued
+  to a client and before the server stops.  Using this option is
+  not recommended.
+
 			Changes since 4.2.5
 
 - Address static analysis warnings.

includes/dhcpd.h

@@ -732,6 +732,7 @@ struct lease_state {
 #endif
 #endif
 #define SV_CACHE_THRESHOLD		78
+#define SV_DONT_USE_FSYNC		79
 
 #if !defined (DEFAULT_PING_TIMEOUT)
 # define DEFAULT_PING_TIMEOUT 1
@@ -1916,6 +1917,7 @@ extern struct timeval cur_tv;
 #define cur_time cur_tv.tv_sec
 
 extern int ddns_update_style;
+extern int dont_use_fsync;
 
 extern const char *path_dhcpd_conf;
 extern const char *path_dhcpd_db;

server/db.c

@@ -1015,11 +1015,12 @@ int commit_leases ()
 	   just in case the rewrite fails. */
 	if (fflush (db_file) == EOF) {
 		log_info("commit_leases: unable to commit, fflush(): %m");
-		return 0;
+		return (0);
 	}
-	if (fsync (fileno (db_file)) < 0) {
+	if ((dont_use_fsync == 0) &&
+	    (fsync(fileno (db_file)) < 0)) {
 		log_info ("commit_leases: unable to commit, fsync(): %m");
-		return 0;
+		return (0);
 	}
 
 	/* send out all deferred ACKs now */
@@ -1033,7 +1034,7 @@ int commit_leases ()
 		write_time = cur_time;
 		new_lease_file();
 	}
-	return 1;
+	return (1);
 }
 
 /*

server/dhcpd.c

@@ -78,6 +78,7 @@ option server.ddns-rev-domainname = \"in-addr.arpa.\";";
 
 #endif /* NSUPDATE */
 int ddns_update_style;
+int dont_use_fsync = 0; /* 0 = default, use fsync, 1 = don't use fsync */
 
 const char *path_dhcpd_conf = _PATH_DHCPD_CONF;
 const char *path_dhcpd_db = _PATH_DHCPD_DB;
@@ -800,7 +801,7 @@ main(int argc, char **argv) {
 
 void postconf_initialization (int quiet)
 {
-	struct option_state *options = (struct option_state *)0;
+	struct option_state *options = NULL;
 	struct data_string db;
 	struct option_cache *oc;
 	char *s;
@@ -816,9 +817,7 @@ void postconf_initialization (int quiet)
 	memset(&db, 0, sizeof db);
 	oc = lookup_option(&server_universe, options, SV_LEASE_FILE_NAME);
 	if (oc &&
-	    evaluate_option_cache (&db, (struct packet *)0,
+	    evaluate_option_cache(&db, NULL, NULL, NULL, options, NULL,
-				   (struct lease *)0, (struct client_state *)0,
-				   options, (struct option_state *)0,
 				  &global_scope, oc, MDL)) {
 		s = dmalloc(db.len + 1, MDL);
 		if (!s)
@@ -831,9 +830,7 @@ void postconf_initialization (int quiet)
 
 	oc = lookup_option(&server_universe, options, SV_PID_FILE_NAME);
 	if (oc &&
-	    evaluate_option_cache (&db, (struct packet *)0,
+	    evaluate_option_cache(&db, NULL, NULL, NULL, options, NULL,
-				   (struct lease *)0, (struct client_state *)0,
-				   options, (struct option_state *)0,
 				  &global_scope, oc, MDL)) {
 		s = dmalloc(db.len + 1, MDL);
 		if (!s)
@@ -853,9 +850,8 @@ void postconf_initialization (int quiet)
                 oc = lookup_option(&server_universe, options,
                                    SV_DHCPV6_LEASE_FILE_NAME);
                 if (oc &&
-                    evaluate_option_cache(&db, NULL, NULL, NULL,
+                    evaluate_option_cache(&db, NULL, NULL, NULL, options, NULL,
-				          options, NULL, &global_scope,
+					  &global_scope, oc, MDL)) {
-                                          oc, MDL)) {
                         s = dmalloc(db.len + 1, MDL);
                         if (!s)
                                 log_fatal("no memory for lease db filename.");
@@ -868,9 +864,8 @@ void postconf_initialization (int quiet)
                 oc = lookup_option(&server_universe, options,
                                    SV_DHCPV6_PID_FILE_NAME);
                 if (oc &&
-                    evaluate_option_cache(&db, NULL, NULL, NULL,
+                    evaluate_option_cache(&db, NULL, NULL, NULL, options, NULL,
-				          options, NULL, &global_scope,
+					  &global_scope, oc, MDL)) {
-                                          oc, MDL)) {
                         s = dmalloc(db.len + 1, MDL);
                         if (!s)
                                 log_fatal("no memory for pid filename.");
@@ -885,9 +880,7 @@ void postconf_initialization (int quiet)
 	omapi_port = -1;
 	oc = lookup_option(&server_universe, options, SV_OMAPI_PORT);
 	if (oc &&
-	    evaluate_option_cache (&db, (struct packet *)0,
+	    evaluate_option_cache(&db, NULL, NULL, NULL, options, NULL,
-				   (struct lease *)0, (struct client_state *)0,
-				   options, (struct option_state *)0,
 				  &global_scope, oc, MDL)) {
 		if (db.len == 2) {
 			omapi_port = getUShort(db.data);
@@ -898,10 +891,7 @@ void postconf_initialization (int quiet)
 
 	oc = lookup_option(&server_universe, options, SV_OMAPI_KEY);
 	if (oc &&
-	    evaluate_option_cache (&db, (struct packet *)0,
+	    evaluate_option_cache(&db, NULL, NULL, NULL, options, NULL,
-				   (struct lease *)0, (struct client_state *)0,
-				   options,
-				   (struct option_state *)0,
 				  &global_scope, oc, MDL)) {
 		s = dmalloc(db.len + 1, MDL);
 		if (!s)
@@ -918,10 +908,7 @@ void postconf_initialization (int quiet)
 
 	oc = lookup_option(&server_universe, options, SV_LOCAL_PORT);
 	if (oc &&
-	    evaluate_option_cache (&db, (struct packet *)0,
+	    evaluate_option_cache(&db, NULL, NULL, NULL, options, NULL,
-				   (struct lease *)0, (struct client_state *)0,
-				   options,
-				   (struct option_state *)0,
 				  &global_scope, oc, MDL)) {
 		if (db.len == 2) {
 			local_port = htons(getUShort (db.data));
@@ -932,9 +919,7 @@ void postconf_initialization (int quiet)
 
 	oc = lookup_option(&server_universe, options, SV_REMOTE_PORT);
 	if (oc &&
-	    evaluate_option_cache (&db, (struct packet *)0,
+	    evaluate_option_cache(&db, NULL, NULL, NULL, options, NULL,
-				   (struct lease *)0, (struct client_state *)0,
-				   options, (struct option_state *)0,
 				  &global_scope, oc, MDL)) {
 		if (db.len == 2) {
 			remote_port = htons(getUShort (db.data));
@@ -946,9 +931,7 @@ void postconf_initialization (int quiet)
 	oc = lookup_option(&server_universe, options,
 			   SV_LIMITED_BROADCAST_ADDRESS);
 	if (oc &&
-	    evaluate_option_cache (&db, (struct packet *)0,
+	    evaluate_option_cache(&db, NULL, NULL, NULL, options, NULL,
-				   (struct lease *)0, (struct client_state *)0,
-				   options, (struct option_state *)0,
 				  &global_scope, oc, MDL)) {
 		if (db.len == 4) {
 			memcpy(&limited_broadcast, db.data, 4);
@@ -957,12 +940,9 @@ void postconf_initialization (int quiet)
 		data_string_forget(&db, MDL);
 	}
 
-	oc = lookup_option (&server_universe, options,
+	oc = lookup_option(&server_universe, options, SV_LOCAL_ADDRESS);
-			    SV_LOCAL_ADDRESS);
 	if (oc &&
-	    evaluate_option_cache (&db, (struct packet *)0,
+	    evaluate_option_cache(&db, NULL, NULL, NULL, options, NULL,
-				   (struct lease *)0, (struct client_state *)0,
-				   options, (struct option_state *)0,
 				  &global_scope, oc, MDL)) {
 		if (db.len == 4) {
 			memcpy(&local_address, db.data, 4);
@@ -973,11 +953,7 @@ void postconf_initialization (int quiet)
 
 	oc = lookup_option(&server_universe, options, SV_DDNS_UPDATE_STYLE);
 	if (oc) {
-		if (evaluate_option_cache (&db, (struct packet *)0,
+		if (evaluate_option_cache(&db, NULL, NULL, NULL, options, NULL,
-					   (struct lease *)0,
-					   (struct client_state *)0,
-					   options,
-					   (struct option_state *)0,
 					  &global_scope, oc, MDL)) {
 			if (db.len == 1) {
 				ddns_update_style = db.data[0];
@@ -1002,11 +978,7 @@ void postconf_initialization (int quiet)
 
 	oc = lookup_option(&server_universe, options, SV_LOG_FACILITY);
 	if (oc) {
-		if (evaluate_option_cache (&db, (struct packet *)0,
+		if (evaluate_option_cache(&db, NULL, NULL, NULL, options, NULL,
-					   (struct lease *)0,
-					   (struct client_state *)0,
-					   options,
-					   (struct option_state *)0,
 					  &global_scope, oc, MDL)) {
 			if (db.len == 1) {
 				closelog ();
@@ -1058,6 +1030,14 @@ void postconf_initialization (int quiet)
 		data_string_forget(&db, MDL);
 	}
 
+	oc = lookup_option(&server_universe, options, SV_DONT_USE_FSYNC);
+	if ((oc != NULL) &&
+	    evaluate_boolean_option_cache(NULL, NULL, NULL, NULL, options, NULL,
+					  &global_scope, oc, MDL)) {
+		dont_use_fsync = 1;
+		log_error("Not using fsync() to flush lease writes");
+	}
+
 	/* Don't need the options anymore. */
 	option_state_dereference(&options, MDL);
 }

server/dhcpd.conf.5

@@ -2110,6 +2110,24 @@ will still honor the setting of the \fBclient-updates\fR flag.
 .RE
 .PP
 The
+.I dont-use-async
+statement
+.RS 0.25i
+.PP
+.B dont-use-async \fIflag\fB;\fR
+.PP
+The \fIdont-use-async\fR statement instructs the DHCP server if
+it should call fsync() when writing leases to the lease file.  By
+default and if the flag is set to false the server \fBwill\fR call
+fsync().  Suppressing the call to fsync() may increase the performance
+of the server but it also adds a risk that a lease will not be
+properly written to the disk after it has been issued to a client
+and before the server stops.  This can lead to duplicate leases
+being issued to different clients.  Using this option is \fBnot
+recommended\FR.
+.RE
+.PP
+The
 .I dynamic-bootp-lease-cutoff
 statement
 .RS 0.25i

server/stables.c

@@ -267,6 +267,7 @@ static struct option server_options[] = {
 #endif /* LDAP_USE_SSL */
 #endif /* LDAP_CONFIGURATION */
 	{ "dhcp-cache-threshold", "B",		&server_universe,  78, 1 },
+	{ "dont-use-fsync", "f",		&server_universe,  79, 1 },
 	{ NULL, NULL, NULL, 0, 0 }
 };