Observability: listen queue backlog

4 files changed, 38 insertions, 7 deletions

diff --git a/src/src/daemon.c b/src/src/daemon.c
index 626b43538..2d8b223c4 100644
--- a/src/src/daemon.c
+++ b/src/src/daemon.c
@@ -396,12 +396,18 @@ if (pid == 0)
   int save_debug_selector = debug_selector;
   BOOL local_queue_only;
   BOOL session_local_queue_only;
-  #ifdef SA_NOCLDWAIT
+#ifdef SA_NOCLDWAIT
   struct sigaction act;
-  #endif
+#endif
 
   smtp_accept_count++;    /* So that it includes this process */
 
+  /* If the listen backlog was over the monitoring level, log it. */
+
+  if (smtp_listen_backlog > smtp_backlog_monitor)
+    log_write(0, LOG_MAIN, "listen backlog %d I=[%s]:%d",
+		smtp_listen_backlog, interface_address, interface_port);
+
   /* May have been modified for the subprocess */
 
   *log_selector = save_log_selector;
@@ -685,6 +691,7 @@ if (pid == 0)
         (void)fclose(smtp_in);
 	(void)close(fileno(smtp_out));
         (void)fclose(smtp_out);
+	smtp_in = smtp_out = NULL;
 
         /* Don't ever molest the parent's SSL connection, but do clean up
         the data structures if necessary. */
@@ -2493,12 +2500,31 @@ for (;;)
 	  }
 	while (check_lsk < listen_socket_count)
 	  {
-	  int sk = check_lsk++;
-          if (FD_ISSET(listen_sockets[sk], &fds))
+	  int lfd = listen_sockets[check_lsk++];
+          if (FD_ISSET(lfd, &fds))
             {
-	    EXIM_SOCKLEN_T len = sizeof(accepted);
-            accept_socket = accept(listen_sockets[sk],
-              (struct sockaddr *)&accepted, &len);
+	    EXIM_SOCKLEN_T alen = sizeof(accepted);
+	    struct tcp_info ti;
+	    socklen_t tlen = sizeof(ti);
+
+	    /* If monitoring the backlog is wanted, grab for later logging */
+
+	    smtp_listen_backlog = 0;
+#if defined(TCP_INFO)
+	    if (  smtp_backlog_monitor > 0
+	       && getsockopt(lfd, IPPROTO_TCP, TCP_INFO, &ti, &tlen) == 0)
+	      {
+	      DEBUG(D_interface) debug_printf("listen fd %d queue max %u curr %u\n",
+# ifdef EXIM_HAVE_TCPI_UNACKED
+		      lfd, ti.tcpi_sacked, ti.tcpi_unacked);
+	      smtp_listen_backlog = ti.tcpi_unacked;
+# elif defined(__FreeBSD__)	/* This does not work. Investigate kernel sourcecode. */
+		      lfd, ti.__tcpi_sacked, ti.__tcpi_unacked);
+	      smtp_listen_backlog = ti.__tcpi_unacked;
+# endif
+	      }
+#endif
+            accept_socket = accept(lfd, (struct sockaddr *)&accepted, &alen);
             break;
             }
 	  }
diff --git a/src/src/globals.c b/src/src/globals.c
index e1837b67d..ef7063ddd 100644
--- a/src/src/globals.c
+++ b/src/src/globals.c
@@ -1471,6 +1471,7 @@ int     smtp_accept_queue      = 0;
 int     smtp_accept_queue_per_connection = 10;
 int     smtp_accept_reserve    = 0;
 uschar *smtp_active_hostname   = NULL;
+int	smtp_backlog_monitor   = 0;
 uschar *smtp_banner            = US"$smtp_active_hostname ESMTP "
                              "Exim $version_number $tod_full"
                              "\0<---------------Space to patch smtp_banner->";
@@ -1483,6 +1484,7 @@ int     smtp_connect_backlog   = 20;
 double  smtp_delay_mail        = 0.0;
 double  smtp_delay_rcpt        = 0.0;
 FILE   *smtp_in                = NULL;
+int     smtp_listen_backlog    = 0;
 int     smtp_load_reserve      = -1;
 int     smtp_mailcmd_count     = 0;
 FILE   *smtp_out               = NULL;
diff --git a/src/src/globals.h b/src/src/globals.h
index 4beb9d07e..c7a2635af 100644
--- a/src/src/globals.h
+++ b/src/src/globals.h
@@ -945,6 +945,7 @@ extern int     smtp_accept_queue;      /* Queue after so many connections */
 extern int     smtp_accept_queue_per_connection; /* Queue after so many msgs */
 extern int     smtp_accept_reserve;    /* Reserve these SMTP connections */
 extern uschar *smtp_active_hostname;   /* Hostname for this message */
+extern int     smtp_backlog_monitor;   /* listen backlog level to log */
 extern uschar *smtp_banner;            /* Banner string (to be expanded) */
 extern BOOL    smtp_check_spool_space; /* TRUE to check SMTP SIZE value */
 extern int     smtp_ch_index;          /* Index in smtp_connection_had */
@@ -959,6 +960,7 @@ extern BOOL    smtp_enforce_sync;      /* Enforce sync rules */
 extern uschar *smtp_etrn_command;      /* Command to run */
 extern BOOL    smtp_etrn_serialize;    /* Only one at once */
 extern FILE   *smtp_in;                /* Incoming SMTP input file */
+extern int     smtp_listen_backlog;    /* Current listener socket backlog, if monitored */
 extern int     smtp_load_reserve;      /* Only from reserved if load > this */
 extern int     smtp_mailcmd_count;     /* Count of MAIL commands */
 extern int     smtp_max_synprot_errors;/* Max syntax/protocol errors */
diff --git a/src/src/readconf.c b/src/src/readconf.c
index 816133329..6d7e7a19e 100644
--- a/src/src/readconf.c
+++ b/src/src/readconf.c
@@ -309,6 +309,7 @@ static optionlist optionlist_config[] = {
   { "smtp_accept_queue_per_connection", opt_int, {&smtp_accept_queue_per_connection} },
   { "smtp_accept_reserve",      opt_int,         {&smtp_accept_reserve} },
   { "smtp_active_hostname",     opt_stringptr,   {&raw_active_hostname} },
+  { "smtp_backlog_monitor",     opt_int,         {&smtp_backlog_monitor} },
   { "smtp_banner",              opt_stringptr,   {&smtp_banner} },
   { "smtp_check_spool_space",   opt_bool,        {&smtp_check_spool_space} },
   { "smtp_connect_backlog",     opt_int,         {&smtp_connect_backlog} },