Rwhod inefficency fix

[dpk at BRL-VGR.ARPA]

Subject: Efficiency fix: Rwhod unnecessarily nlists the kernel
Index:	 etc/rwhod/rwhod.c 4.2BSD FIX

Description:
	Rwhod was nlisting the kernel every 10*sleep_interval
seconds whether it needed to or not.  This caused it to consume
far more CPU and disk I/O than it should have.

Repeat-By:
	Run "sa" and look at the stats for "rwhod".

Fix:
	The following diff lists shows some code (~12 lines) which
should be added to the top of getkmem().  This code will check to see
when kernel file has been changed by stating the file and comparing the
last inode change time with the current inode change time (it also
checks the inode number).  This feature of looking for vmunix to change
is so that rwhod can eventually get the load average information even if
you boot up an alternate kernel.  The assumption is that you will copy
or link the kernel you booted to /vmunix.  The line numbers will be offset
by a few lines do to a header we add to the files.

323a335,348
> 	struct stat statb;
> 	static time_t unixctime = 0L;
> 	static ino_t unixinode;
> 
> 	if (stat ("/vmunix", &statb) < 0) {
> 		if (unixctime != 0L)
> 			return;		/* get new values later ... */
> 	}
> 	else if (unixctime != statb.st_ctime || unixinode != statb.st_ino) {
> 		unixctime = statb.st_ctime;		/* we're updating */
> 		unixinode = statb.st_ino;
> 	}
> 	else
> 		return;