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ntpd: improve treatment of DNS resolution failures

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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>
This commit is contained in:
Denys Vlasenko 2017-10-31 12:44:37 +01:00
parent 518fb3ba19
commit 6a4f223122
1 changed files with 33 additions and 15 deletions
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48
networking/ntpd.c
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@ -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;
}