bump descriptors limit to the max and set the maximum connections count to

three quarters of that limit (a session typically has 3 descriptors). when
we hit that limit, we stop accepting connections, and when client closes a
session, we start accepting connections again. this prevents us from going
into a session that is likely to fail because of scarce resources.

idea discussed with jacekm@, code mostly ripped from relayd

4 files changed, 34 insertions, 9 deletions

diff --git a/usr.sbin/smtpd/smtp.c b/usr.sbin/smtpd/smtp.c
index 0f5f24c18fb..a2338ab4353 100644
--- a/usr.sbin/smtpd/smtp.c
+++ b/usr.sbin/smtpd/smtp.c
@@ -1,4 +1,4 @@
-/*	$OpenBSD: smtp.c,v 1.19 2009/01/30 16:37:52 gilles Exp $	*/
+/*	$OpenBSD: smtp.c,v 1.20 2009/01/30 17:34:58 gilles Exp $	*/
 
 /*
  * Copyright (c) 2008 Gilles Chehade <gilles@openbsd.org>
@@ -698,7 +698,7 @@ smtp_accept(int fd, short event, void *p)
 	log_debug("smtp_accept: incoming client on listener: %p", l);
 	len = sizeof(struct sockaddr_storage);
 	if ((s_fd = accept(l->fd, (struct sockaddr *)&ss, &len)) == -1) {
-		event_add(&l->ev, NULL);
+		event_del(&l->ev);
 		return;
 	}
 
@@ -709,10 +709,18 @@ smtp_accept(int fd, short event, void *p)
 
 	s->s_fd = s_fd;
 	s->s_tm = time(NULL);
+	s->s_env = l->env;
+	s->s_l = l;
+
 	(void)memcpy(&s->s_ss, &ss, sizeof(s->s_ss));
 
 	session_init(l, s);
 	event_add(&l->ev, NULL);
+
+	s_smtp.clients++;
+
+	if (s_smtp.clients == s->s_env->sc_maxconn)
+		event_del(&l->ev);
 }
 
 void
diff --git a/usr.sbin/smtpd/smtp_session.c b/usr.sbin/smtpd/smtp_session.c
index 1340cc703e5..3b1a6552371 100644
--- a/usr.sbin/smtpd/smtp_session.c
+++ b/usr.sbin/smtpd/smtp_session.c
@@ -1,4 +1,4 @@
-/*	$OpenBSD: smtp_session.c,v 1.48 2009/01/30 16:37:52 gilles Exp $	*/
+/*	$OpenBSD: smtp_session.c,v 1.49 2009/01/30 17:34:58 gilles Exp $	*/
 
 /*
  * Copyright (c) 2008 Gilles Chehade <gilles@openbsd.org>
@@ -748,12 +748,8 @@ void
 session_init(struct listener *l, struct session *s)
 {
 	s->s_state = S_INIT;
-	s->s_env = l->env;
-	s->s_l = l;
 	s->s_id = queue_generate_id();
 
-	s_smtp.clients++;
-
 	if ((s->s_bev = bufferevent_new(s->s_fd, session_read, session_write,
 	    session_error, s)) == NULL)
 		fatalx("session_init: bufferevent_new failed");
@@ -912,6 +908,8 @@ session_destroy(struct session *s)
 	close(s->s_fd);
 
 	s_smtp.clients--;
+	if (s_smtp.clients < s->s_env->sc_maxconn)
+		event_add(&s->s_l->ev, NULL);
 
 	if (s->s_bev != NULL) {
 		bufferevent_free(s->s_bev);
diff --git a/usr.sbin/smtpd/smtpd.c b/usr.sbin/smtpd/smtpd.c
index 6f13c500d39..4dbfcaa5c0c 100644
--- a/usr.sbin/smtpd/smtpd.c
+++ b/usr.sbin/smtpd/smtpd.c
@@ -1,4 +1,4 @@
-/*	$OpenBSD: smtpd.c,v 1.28 2009/01/30 10:03:29 form Exp $	*/
+/*	$OpenBSD: smtpd.c,v 1.29 2009/01/30 17:34:58 gilles Exp $	*/
 
 /*
  * Copyright (c) 2008 Gilles Chehade <gilles@openbsd.org>
@@ -25,6 +25,7 @@
 #include <sys/wait.h>
 #include <sys/stat.h>
 #include <sys/uio.h>
+#include <sys/resource.h>
 
 #include <bsd_auth.h>
 #include <err.h>
@@ -591,6 +592,7 @@ main(int argc, char *argv[])
 	struct event	 ev_sigchld;
 	struct event	 ev_sighup;
 	struct timeval	 tv;
+	struct rlimit	 rl;
 	struct peer	 peers[] = {
 		{ PROC_CONTROL,	parent_dispatch_control },
 		{ PROC_LKA,	parent_dispatch_lka },
@@ -659,6 +661,22 @@ main(int argc, char *argv[])
 
 	log_info("startup%s", (debug > 1)?" [debug mode]":"");
 
+	if (getrlimit(RLIMIT_NOFILE, &rl) == -1)
+		fatal("smtpd: failed to get resource limit");
+
+	log_debug("smtpd: max open files %lld", rl.rlim_max);
+
+	/*
+	 * Allow the maximum number of open file descriptors for this
+	 * login class (which should be the class "daemon" by default).
+	 */
+	rl.rlim_cur = rl.rlim_max;
+	if (setrlimit(RLIMIT_NOFILE, &rl) == -1)
+		fatal("smtpd: failed to set resource limit");
+
+	env.sc_maxconn = (rl.rlim_cur / 4) * 3;
+	log_debug("smtpd: will accept at most %d clients", env.sc_maxconn);
+
 	init_peers(&env);
 
 	/* start subprocesses */
diff --git a/usr.sbin/smtpd/smtpd.h b/usr.sbin/smtpd/smtpd.h
index 60b50aa413d..2c6da0c217d 100644
--- a/usr.sbin/smtpd/smtpd.h
+++ b/usr.sbin/smtpd/smtpd.h
@@ -1,4 +1,4 @@
-/*	$OpenBSD: smtpd.h,v 1.63 2009/01/30 16:37:52 gilles Exp $	*/
+/*	$OpenBSD: smtpd.h,v 1.64 2009/01/30 17:34:58 gilles Exp $	*/
 
 /*
  * Copyright (c) 2008 Gilles Chehade <gilles@openbsd.org>
@@ -624,6 +624,7 @@ struct smtpd {
 #define SMTPD_SMTP_PAUSED		       	 0x00000010
 	u_int32_t				 sc_flags;
 	struct timeval				 sc_qintval;
+	u_int32_t				 sc_maxconn;
 	struct event				 sc_ev;
 	int					 sc_pipes[PROC_COUNT]
 						    [PROC_COUNT][2];