6a4f22312
Denys Vlasenko
2017-10-31
Subject
ntpd: improve treatment of DNS resolution failures
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networking/ntpd.c+33 -15
| @@ -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; | |
| } | |