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Check for carrier before sendto() or write() on interface fd.

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Linux will quietly proceed as if the data were sent even if the carrier
is down and nothing actually happened.  There is still a tiny race
condition where the carrier could drop between the check and the actual
write, but we really can't do anything about that and it is a very
small race.
This commit is contained in:
Nicholas J. Kain
2015-02-13 21:53:15 -05:00
parent 911d4cc58e
commit b4b6ed8fd5
4 changed files with 44 additions and 2 deletions
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11
src/arp.c
View File

@ -257,8 +257,14 @@ static int arp_send(struct client_state_t *cs, struct arpMsg *arp)
return -1;
}
ssize_t r = safe_sendto(cs->arpFd, (const char *)arp, sizeof *arp,
0, (struct sockaddr *)&addr, sizeof addr);
ssize_t r;
if (!check_carrier(cs->arpFd)) {
log_error("%s: (%s) carrier down; sendto would fail",
client_config.interface, __func__);
goto carrier_down;
}
r = safe_sendto(cs->arpFd, (const char *)arp, sizeof *arp, 0,
(struct sockaddr *)&addr, sizeof addr);
if (r < 0 || (size_t)r != sizeof *arp) {
if (r < 0)
log_error("%s: (%s) sendto failed: %s",
@ -266,6 +272,7 @@ static int arp_send(struct client_state_t *cs, struct arpMsg *arp)
else
log_error("%s: (%s) sendto short write: %z < %zu",
client_config.interface, __func__, r, sizeof *arp);
carrier_down:
arp_reopen_fd(cs);
return -1;
}