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ntpd: retry initial DNS resolution (forever, no timeout for now). 

Some users start ntpd on boot, and don't babysit it. If it dies because
DNS is not yet up and therefore NTP servers can't be found, users are
not happy.

Example behavior with a peer name which can't be resolved:

ntpd: bad address 'qwe.rty.ghj.kl'
...5 sec...
ntpd: bad address 'qwe.rty.ghj.kl'
ntpd: bad address 'qwe.rty.ghj.kl'
ntpd: bad address 'qwe.rty.ghj.kl'
ntpd: bad address 'qwe.rty.ghj.kl'
ntpd: bad address 'qwe.rty.ghj.kl'
ntpd: bad address 'qwe.rty.ghj.kl'
ntpd: bad address 'qwe.rty.ghj.kl'
ntpd: bad address 'qwe.rty.ghj.kl'
ntpd: bad address 'qwe.rty.ghj.kl'
...

Based on the patch by Kaarle Ritvanen <kaarle.ritvanen@datakunkku.fi>

function                                             old     new   delta
resolve_peer_hostname                                  -      81     +81
ntpd_main                                           1130    1061     -69
------------------------------------------------------------------------------
(add/remove: 1/0 grow/shrink: 0/1 up/down: 81/-69)             Total: 12 bytes

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
This commit is contained in:
Denys Vlasenko 2016-06-06 02:26:49 +02:00
parent b684d1b186
commit e4caf1dd9c
1 changed files with 30 additions and 17 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

47
networking/ntpd.c
View File

@ -267,7 +267,6 @@ typedef struct {
typedef struct {
len_and_sockaddr *p_lsa;
char *p_hostname;
char *p_dotted;
int p_fd;
int datapoint_idx;
@ -293,6 +292,7 @@ typedef struct {
datapoint_t filter_datapoint[NUM_DATAPOINTS];
/* last sent packet: */
msg_t p_xmt_msg;
char p_hostname[1];
} peer_t;
@ -764,15 +764,39 @@ reset_peer_stats(peer_t *p, double offset)
VERB6 bb_error_msg("%s->lastpkt_recv_time=%f", p->p_dotted, p->lastpkt_recv_time);
}
static void
resolve_peer_hostname(peer_t *p, int loop_on_fail)
{
len_and_sockaddr *lsa;
again:
lsa = host2sockaddr(p->p_hostname, 123);
if (!lsa) {
/* error message already emitted by host2sockaddr() */
if (!loop_on_fail)
return;
//FIXME: do this to avoid infinite looping on typo in a hostname?
//well... in which case, what is a good value for loop_on_fail?
//if (--loop_on_fail == 0)
// xfunc_die();
sleep(5);
goto again;
}
free(p->p_lsa);
free(p->p_dotted);
p->p_lsa = lsa;
p->p_dotted = xmalloc_sockaddr2dotted_noport(&lsa->u.sa);
}
static void
add_peers(const char *s)
{
llist_t *item;
peer_t *p;
p = xzalloc(sizeof(*p));
p->p_lsa = xhost2sockaddr(s, 123);
p->p_dotted = xmalloc_sockaddr2dotted_noport(&p->p_lsa->u.sa);
p = xzalloc(sizeof(*p) + strlen(s));
strcpy(p->p_hostname, s);
resolve_peer_hostname(p, /*loop_on_fail=*/ 1);
/* Names like N.<country2chars>.pool.ntp.org are randomly resolved
* to a pool of machines. Sometimes different N's resolve to the same IP.
@ -789,7 +813,6 @@ add_peers(const char *s)
}
}
p->p_hostname = xstrdup(s);
p->p_fd = -1;
p->p_xmt_msg.m_status = MODE_CLIENT | (NTP_VERSION << 3);
p->next_action_time = G.cur_time; /* = set_next(p, 0); */
@ -2338,18 +2361,8 @@ int ntpd_main(int argc UNUSED_PARAM, char **argv)
p->p_dotted, p->reachable_bits, timeout);
/* What if don't see it because it changed its IP? */
if (p->reachable_bits == 0) {
len_and_sockaddr *lsa = host2sockaddr(p->p_hostname, 123);
if (lsa) {
char *dotted = xmalloc_sockaddr2dotted_noport(&lsa->u.sa);
//if (strcmp(dotted, p->p_dotted) != 0)
// bb_error_msg("peer IP changed");
free(p->p_lsa);
free(p->p_dotted);
p->p_lsa = lsa;
p->p_dotted = dotted;
}
}
if (p->reachable_bits == 0)
resolve_peer_hostname(p, /*loop_on_fail=*/ 0);
set_next(p, timeout);
}