tsleep_nsec(9): add MAXTSLP macro, the maximum sleep duration

This macro will be useful for truncating durations below INFSLP
(UINT64_MAX) when converting from a timespec or timeval to a count
of nanoseconds before calling tsleep_nsec(9), msleep_nsec(9), or
rwsleep_nsec(9).

A relative timespec can hold many more nanoseconds than a uint64_t
can.  TIMESPEC_TO_NSEC() and TIMEVAL_TO_NSEC() check for overflow,
returning UINT64_MAX if the conversion would overflow a uint64_t.

Thus, MAXTSLP will make it easy to avoid inadvertently passing INFSLP
to tsleep_nsec(9) et al. when the caller intended to set a timeout.

The code in such a case might look something like this:

	uint64_t nsecs = MIN(TIMESPEC_TO_NSEC(&ts), MAXTSLP);

The macro may also be useful for rejecting intervals that are "too large",
e.g. for sockets with timeouts, if the timeout duration is to be stored
as a uint64_t in an object in the kernel.  The code in such a case might
look something like this:

	case SIOCTIMEOUT:
	{
		struct timeval *tv = (struct timeval *)data;
		uint64_t nsecs;

		if (tv->tv_sec < 0 || !timerisvalid(tv))
			return EINVAL;

		nsecs = TIMEVAL_TO_NSEC(tv);
		if (nsecs > MAXTSLP)
			return EOVERFLOW;

		obj.timeout = nsecs;
		break;
	}

Idea suggested by visa@.

ok visa@

0 files changed, 0 insertions, 0 deletions