[ntp:hackers] nonblocking DNS code nearly complete

Dave Hart davehart at gmail.com
Sun Jan 10 21:28:48 UTC 2010


On Mon, Jun 1, 2009 Dave Hart wrote:
>                        getaddrinfo_sometime(curr_peer->addr->address, "ntp",
>                                             &hints, 2, peer_name_resolved,
>                                             (void *)curr_peer);
> void
> peer_name_resolved(
>        int                     retcode,
>        int                     gai_errno,
>        void *                  context,
>        const char *            name,
>        const char *            service,
>        const struct addrinfo * ai_in,
>        const struct addrinfo * res
>        )
> {

About 6 months ago I sidelined a prototype of a replacement for
ntp_intres with its funky temporary file and mode 7 to 127.0.0.1
interface, deeming it too disruptive for the looming 4.2.6 release.
With 4.2.6 out and a bunch of the initial hiccups smoothed over, I
spent some time merging the intervening changes.  I also added a
previously-missing piece, forking off the child worker on demand and
idling it out when there are no more DNS queries remaining.

Aside from some cleanup and shuffling of code between files, the only
other item I'd like to see is optional support for using pthreads and
directly sharing pointers instead of fork() and serializing over a
pipe on POSIXy systems.  That seems like an item that can wait, and it
might be best to wait to flush out bugs in the fork-based code first.
It would be most useful on systems that support pthreads but not
fork(), including some embedded Linux solutions.

As the quoted code above shows, the interface presented to DNS
consumer code in ntpd is based on getaddrinfo() with a callback
routine invoked later via the I/O loop when the query results are
ready.  Unlike some options for achieving asynchronous DNS, this code
simply uses the standard getaddrinfo() interface provided by the
system, rather than attempt to replace it with UDP/TCP 53 queries.

I believe the code works better than the current intres now, in that
all DNS queries are performed without blocking the daemon, including
the first queries which block the daemon in the current code.  I would
appreciate testing and feedback.

The code is in ~hart/ntp-dev-block on pogo and psp-deb1, and also in
~hart/ntp-4.2.7p2-new-intres.tar.gz on both.  It can also be
downloaded from:

http://davehart.net/ntp/dns/ntp-4.2.7p2-new-intres.tar.gz

MD5 hash: 13ab2f7b760f287928a72486b63388a2

Cheers,
Dave Hart


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