Re: [dev][sdhcp] more updates

From: Michael Forney <mforney_AT_mforney.org>
Date: Sat, 2 Feb 2019 22:28:33 -0800

On 2019-02-02, Sean MacLennan <seanm_AT_seanm.ca> wrote:
> First a question: how portable do we want things? The current sdhcp
> works only on Linux.

I think that depends on how feasible it is to make it portable without
relying on a bunch of ifdefs to support different platforms.

In terms of timerfd, I think it should be okay to use POSIX timers and
a self-pipe (like that patch I sent you a while back), but it is kind
of ugly to have to recreate the timers after the fork. Personally, I
don't see much value in having sdhcp fork; I always run it with a
service supervisor.

CLOCK_BOOTTIME is pretty important for being able to resume from
suspend, but I'm not sure how portable this is. It looks like OpenBSD
has it, but not FreeBSD. Maybe this could be an option in a config.h?

> * calctimeout() was dividing the timeout by 2. Not sure why so I
> removed it. Also, the check for less than 60 seconds would only
> work if you went back in time to Jan 1, 1970 for the first minute
> after midnight.

Check the comment for the calctimeout() function. It sets the
itimerspec passed by the caller to half-way until the expiration of
the specified timer. The struct itimerspec here specifies a time
*duration*, not a time instant, so I don't think 1970 has anything to
do with it.

The function uses timerfd_gettime to determine the duration of time
left until timer `n` expires, then sets `ts` to half of that duration,
down to a minimum of 60 seconds. This is what RFC 2131 says to do:

   In both RENEWING and REBINDING states, if the client receives no
   response to its DHCPREQUEST message, the client SHOULD wait one-half
   of the remaining time until T2 (in RENEWING state) and one-half of
   the remaining lease time (in REBINDING state), down to a minimum of
   60 seconds, before retransmitting the DHCPREQUEST message.
Received on Sun Feb 03 2019 - 07:28:33 CET