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authorDenys Vlasenko2017-10-31 12:44:37 +0100
committerDenys Vlasenko2017-10-31 12:44:37 +0100
commit6a4f2231221c2c4f7ca82f081f442e31a6cfd051 (patch)
treef46898d1c966061177d82cb02be2ecf7aee0024f
parent518fb3ba193cddc1369090bfdf827618b42791db (diff)
downloadbusybox-6a4f2231221c2c4f7ca82f081f442e31a6cfd051.zip
busybox-6a4f2231221c2c4f7ca82f081f442e31a6cfd051.tar.gz
ntpd: improve treatment of DNS resolution failures
function old new delta ntpd_main 1106 1177 +71 resolve_peer_hostname 122 127 +5 ------------------------------------------------------------------------------ (add/remove: 0/0 grow/shrink: 2/0 up/down: 76/0) Total: 76 bytes Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
-rw-r--r--networking/ntpd.c48
1 files changed, 33 insertions, 15 deletions
diff --git a/networking/ntpd.c b/networking/ntpd.c
index 8f792d1..e0c9810 100644
--- a/networking/ntpd.c
+++ b/networking/ntpd.c
@@ -155,7 +155,8 @@
#define RETRY_INTERVAL 32 /* on send/recv error, retry in N secs (need to be power of 2) */
#define NOREPLY_INTERVAL 512 /* sent, but got no reply: cap next query by this many seconds */
#define RESPONSE_INTERVAL 16 /* wait for reply up to N secs */
-#define HOSTNAME_INTERVAL 5 /* hostname lookup failed. Wait N secs for next try */
+#define HOSTNAME_INTERVAL 4 /* hostname lookup failed. Wait N * peer->dns_errors secs for next try */
+#define DNS_ERRORS_CAP 0x3f /* peer->dns_errors is in [0..63] */
/* Step threshold (sec). std ntpd uses 0.128.
*/
@@ -301,6 +302,7 @@ typedef struct {
uint8_t lastpkt_status;
uint8_t lastpkt_stratum;
uint8_t reachable_bits;
+ uint8_t dns_errors;
/* when to send new query (if p_fd == -1)
* or when receive times out (if p_fd >= 0): */
double next_action_time;
@@ -802,10 +804,9 @@ resolve_peer_hostname(peer_t *p)
p->p_dotted = xmalloc_sockaddr2dotted_noport(&lsa->u.sa);
VERB1 if (strcmp(p->p_hostname, p->p_dotted) != 0)
bb_error_msg("'%s' is %s", p->p_hostname, p->p_dotted);
- } else {
- /* error message is emitted by host2sockaddr() */
- set_next(p, HOSTNAME_INTERVAL);
+ p->dns_errors = 0;
}
+ p->dns_errors = ((p->dns_errors << 1) | 1) & DNS_ERRORS_CAP;
return lsa;
}
@@ -2358,14 +2359,6 @@ int ntpd_main(int argc UNUSED_PARAM, char **argv)
int nfds, timeout;
double nextaction;
- /* Resolve peer names to IPs, if not resolved yet */
- for (item = G.ntp_peers; item != NULL; item = item->link) {
- peer_t *p = (peer_t *) item->data;
-
- if (p->next_action_time <= G.cur_time && !p->p_lsa)
- resolve_peer_hostname(p);
- }
-
/* Nothing between here and poll() blocks for any significant time */
nextaction = G.cur_time + 3600;
@@ -2447,13 +2440,38 @@ int ntpd_main(int argc UNUSED_PARAM, char **argv)
did_poll:
gettime1900d(); /* sets G.cur_time */
if (nfds <= 0) {
- if (!bb_got_signal /* poll wasn't interrupted by a signal */
- && G.cur_time - G.last_script_run > 11*60
- ) {
+ double ct;
+
+ if (bb_got_signal)
+ break; /* poll was interrupted by a signal */
+
+ if (G.cur_time - G.last_script_run > 11*60) {
/* Useful for updating battery-backed RTC and such */
run_script("periodic", G.last_update_offset);
gettime1900d(); /* sets G.cur_time */
}
+
+ /* Resolve peer names to IPs, if not resolved yet.
+ * We do it only when poll timed out:
+ * this way, we almost never overlap DNS resolution with
+ * "request-reply" packet round trip.
+ */
+ ct = G.cur_time;
+ for (item = G.ntp_peers; item != NULL; item = item->link) {
+ peer_t *p = (peer_t *) item->data;
+ if (p->next_action_time <= ct && !p->p_lsa) {
+ /* This can take up to ~10 sec per each DNS query */
+ resolve_peer_hostname(p);
+ }
+ }
+ gettime1900d(); /* sets G.cur_time (needed for set_next()) */
+ /* Set next time for those which are still not resolved */
+ for (item = G.ntp_peers; item != NULL; item = item->link) {
+ peer_t *p = (peer_t *) item->data;
+ if (p->next_action_time <= ct && !p->p_lsa) {
+ set_next(p, HOSTNAME_INTERVAL * p->dns_errors);
+ }
+ }
goto check_unsync;
}