Issue 6010 - 389 ds ignores nsslapd-maxdescriptors (#6027)

Bug description: During server startup the connection table size is assumed
to be lower than or equal to the number of configured reserve file descriptors.
This prevents the server from starting whem the number of reserve descriptors
is high.

Fix description: Change the check to make sure the connection table size is
not greater than (max descriptors - reserve descriptors).

Also, the number of reserve descriptors is used to determine if the server can
accept a new connection. This has been changed to compare the connection table
size against the current number of connections.

Relates: #6010

Reviewed by: @progier389, @droideck, @tbordaz (Thank you)

dirsrvtests/tests/suites/resource_limits/fdlimits_test.py

@@ -83,7 +83,7 @@ def test_fd_limits(topology_st):
 def test_reserve_descriptor_validation(topology_st):
     """Test the reserve descriptor self check
 
-    :id: TODO
+    :id: 9bacdbcc-7754-4955-8a56-1d8c82bce274
     :setup: Standalone Instance
     :steps:
         1. Set attr nsslapd-reservedescriptors to a low value of RESRV_DESC_VAL (10)
@@ -121,6 +121,41 @@ def test_reserve_descriptor_validation(topology_st):
 
     log.info("test_reserve_descriptor_validation PASSED")
 
+@pytest.mark.skipif(ds_is_older("1.4.1.2"), reason="Not implemented")
+def test_reserve_descriptors_high(topology_st):
+    """Test setting reserve descriptor value to higher than average.
+
+    :id: 19c8991b-ef78-485e-bdf9-a0977fcbcd04
+    :setup: Standalone Instance
+    :steps:
+        1. Set attr nsslapd-maxdescriptors to systemd LimitNOFILE value
+        2. Verify value has been set
+        3. Set attr nsslapd-reservedescriptors to 2 less than nsslapd-maxdescriptors
+        4. Verify value has been set
+        5. Restart instance
+    :expectedresults:
+        1. Success
+        2. Value of SYSTEMD_LIMIT is returned
+        3. Success
+        4. Values of SYSTEMD_LIMIT -2 is returned
+        5. Instance starts correctly
+    """
+
+    # Set nsslapd-maxdescriptors to a custom value
+    topology_st.standalone.config.set(FD_ATTR, SYSTEMD_LIMIT)
+    max_fd = topology_st.standalone.config.get_attr_val_utf8(FD_ATTR)
+    assert max_fd == SYSTEMD_LIMIT
+
+    # Set nsslapd-reservedescriptors to 2 less than custom value
+    topology_st.standalone.config.set(RESRV_FD_ATTR, str(int(SYSTEMD_LIMIT) - 2))
+    resrv_fd = topology_st.standalone.config.get_attr_val_utf8(RESRV_FD_ATTR)
+    assert resrv_fd == str(int(SYSTEMD_LIMIT) - 2)
+
+    # Verify instance restart
+    topology_st.standalone.restart()
+    assert (topology_st.standalone.status())
+
+    log.info("test_reserve_descriptors_high PASSED")
 
 if __name__ == '__main__':
     # Run isolated

ldap/servers/slapd/conntable.c

@@ -122,7 +122,8 @@ connection_table_new(int table_size)
     ct->list_num = config_get_num_listeners();
     ct->num_active = (int *)slapi_ch_calloc(1, ct->list_num * sizeof(int));
     ct->size = table_size - (table_size % ct->list_num);
-    ct->list_size = ct->size/ct->list_num;
+    /* Account for first slot of each list being used as head (c_next).  */
+    ct->list_size = (ct->size/ct->list_num)+1;
     ct->c = (Connection **)slapi_ch_calloc(1, ct->size * sizeof(Connection *));
     ct->fd = (struct POLL_STRUCT **)slapi_ch_calloc(1, ct->list_num * sizeof(struct POLL_STRUCT*));
     ct->table_mutex = PR_NewLock();

ldap/servers/slapd/daemon.c

@@ -817,7 +817,6 @@ accept_thread(void *vports)
     PRErrorCode prerr;
     int last_accept_new_connections = -1;
     PRIntervalTime pr_timeout = PR_MillisecondsToInterval(slapd_accept_wakeup_timer);
-    slapdFrontendConfig_t *slapdFrontendConfig = getFrontendConfig();
     PRFileDesc **n_tcps = NULL;
     PRFileDesc **s_tcps = NULL;
     PRFileDesc **i_unix = NULL;
@@ -831,7 +830,7 @@ accept_thread(void *vports)
 
     while (!g_get_shutdown()) {
         /* Do we need to accept new connections? */
-        int accept_new_connections = ((ct->size - g_get_current_conn_count()) > slapdFrontendConfig->reservedescriptors);
+        int accept_new_connections = (ct->size > ct->conn_next_offset);
         if (!accept_new_connections) {
             if (last_accept_new_connections) {
                 slapi_log_err(SLAPI_LOG_ERR, "accept_thread",
@@ -2083,7 +2082,7 @@ unfurl_banners(Connection_Table *ct, daemon_ports_t *ports, PRFileDesc **n_tcps,
     char addrbuf[256];
     int isfirsttime = 1;
 
-    if (ct->size <= slapdFrontendConfig->reservedescriptors) {
+    if (ct->size > (slapdFrontendConfig->maxdescriptors - slapdFrontendConfig->reservedescriptors)) {
         slapi_log_err(SLAPI_LOG_ERR, "slapd_daemon",
                       "Not enough descriptors to accept any connections. "
                       "This may be because the maxdescriptors configuration "