fix(dnsmasq): make --conf-poll actually wake the loop periodically

poll_dynamic_dirs() was only ever invoked opportunistically, whenever
something else (a DNS/DHCP packet, an inotify event, a signal) already
woke up dnsmasq's main loop. With no such activity, the loop's
do_poll() blocks indefinitely, so on a quiet dnsmasq instance the
poller never actually ran on its own, no matter how long
--conf-poll-interval was set to.

conf-poll.patch now also clamps the loop's wait timeout to
--conf-poll-interval when --conf-poll is set, the same way TFTP/DBus/
DAD already force more frequent wake-ups.

Reproduced against a live pod (dhcp-hostsdir file created from a
different host, dnsmasq never picked it up despite --conf-poll being
set) and verified the fix by running dnsmasq with --conf-poll, no
upstream DNS servers and no DHCP traffic (so nothing else would ever
wake the loop), then confirming a new dhcp-hostsdir file is picked up
within ~1s with zero other interaction with the process.

Author: skrobul

containers/dnsmasq/dnsmasq/conf-poll.patch

@@ -7,6 +7,13 @@ SIGHUP or restart. --conf-poll (with --conf-poll-interval, default 1s)
 adds an opt-in stat-based poll of these directories, running alongside
 inotify and reusing the same reload path.
 
+Also forces the main loop to wake up at least once every
+--conf-poll-interval seconds when --conf-poll is set (the same way
+TFTP/DBus/DAD already force more frequent wake-ups): without any other
+DNS/DHCP/inotify activity, the loop's do_poll() would otherwise block
+indefinitely and the poller would never actually run, no matter how
+long the process had been up.
+
 Rebased against dnsmasq 2.93 (as packaged in Debian forky).
 ---
 diff --git a/man/dnsmasq.8 b/man/dnsmasq.8
@@ -54,7 +61,7 @@ index 099c65f..ea835bb 100644
  .B --dhcp-optsdir=<path>
  This is equivalent to \fB--dhcp-optsfile\fP, with the differences noted for \fB--dhcp-hostsdir\fP.
 diff --git a/src/dnsmasq.c b/src/dnsmasq.c
-index adaa692..f9be116 100644
+index adaa692..4bf4d2c 100644
 --- a/src/dnsmasq.c
 +++ b/src/dnsmasq.c
 @@ -184,8 +184,11 @@ int main (int argc, char **argv)
@@ -70,7 +77,25 @@ index adaa692..f9be116 100644
    if (option_bool(OPT_DNSSEC_VALID))
      {
  #ifdef HAVE_DNSSEC
-@@ -1248,7 +1251,19 @@ int main (int argc, char **argv)
+@@ -1117,7 +1120,16 @@ int main (int argc, char **argv)
+       else if (is_dad_listeners() &&
+ 	       (timeout == -1 || timeout > 1000))
+ 	timeout = 1000;
+-      
++
++      /* --conf-poll: with nothing else to wake the loop (no DNS/DHCP traffic,
++	 no inotify event), do_poll() below would otherwise block indefinitely
++	 and poll_dynamic_dirs(), below, would never get a chance to run. Force
++	 a periodic wake-up so it's actually polled every conf_poll_interval
++	 seconds, not just opportunistically when something else wakes us. */
++      if (option_bool(OPT_CONF_POLL) &&
++	  (timeout == -1 || timeout > daemon->conf_poll_interval * 1000))
++	timeout = daemon->conf_poll_interval * 1000;
++
+       if (daemon->port != 0)
+ 	set_dns_listeners();
+       
+@@ -1248,7 +1260,19 @@ int main (int argc, char **argv)
  	{
  	  if (daemon->port != 0 && !option_bool(OPT_NO_POLL))
  	    poll_resolv(1, 1, now);