dpkg s-s-d --retry --pidfile changes

[Justin Pryzby <jpryzby+d@quoininc.com>]

Hi everyone,

In debian/changelog for dpkg-1.14.16.3:
| * Fix timeout computations for start-stop-daemon --retry option. This has
|   not worked properly for a long time (maybe never), but came to light
|   due to #460903's fix. Closes: #462104

In utils/start-stop-daemon.c (the ! are mine):
|static void
|tmul(struct timeval *a, int b)
|{
|        a->tv_sec *= b;
!        fprintf(stderr, "%d, %ld\n", b, a->tv_usec);
!        assert(a->tv_usec<2000000./b);
|        a->tv_usec *= b;
!        assert(a->tv_usec<2000000);
|        if (a->tv_usec >= 1000000) {
|                ++a->tv_sec;
|                a->tv_usec -= 1000000;
|        }
!        assert(a->tv_usec<1000000);
|}

I wonder whether that "if()" should be a "while()" since b (aka ratio) is
initialized to 1 and incremented (although the comments state that it is
initialized to 2).

Indeed, I was able to make it abort in a few runs by sending sigstop
at strategic places:

|kill(0, SIGSTOP);
|xgettimeofday(&after);

$ sleep 300 & echo $! >./pidfile
[...]
$ fg
./start-stop-daemon --verbose --retry 10 --pidfile ./pidfile --stop --name sleep --signal CONT
3, 896334
start-stop-daemon: start-stop-daemon.c:235: tmul: Assertion `a->tv_usec<2000000./b' failed.
Aborted

Justin