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Darwin 0.2 Driver Kit

			Disk Statistics notes
			
int 	dk_ndrive = DK_NDRIVE;
int 	dk_busy;
long	dk_time[DK_NDRIVE];
long	dk_seek[DK_NDRIVE];
long	dk_xfer[DK_NDRIVE];
long	dk_wds[DK_NDRIVE];
float	dk_mspw[DK_NDRIVE];		// never Used!!!!!!
long	dk_bps[DK_NDRIVE];

SCSI Disk Driver

	dk_bps[dk] set once, in sdsetbratio. Calculated from values in 
		label (dlp->nsect, dlp->dl_secsize, dlp->rpm)
	sdstart:
		dk_busy |= 1 << device;
		dk_xfer[device]++;
		dk_seek[device]++;
		dk_wds[device] += bp->b_bcount >> 6;
		
	sdintr:
		dk_busy &=~ (1 << device);
		
OD driver

	od_read_label:
		dk_bps[dk] = l->dl_secsize * l->dl_nsect *
				l->dl_rpm / 60;

	od_go:
		dk_busy |= 1 << dk;
		dk_xfer[dk]++;
		dk_wds[dk] += bp->b_bcount >> 6;
	
	od_done:
		dk_busy &= ~(1 << dk);
		
	state machine starting seek:
		dk_seek[dk]++;

In gatherstats(), every hardclock (hz times per second?)

	for (s = 0; s < DK_NDRIVE; s++)
		if (dk_busy & (1 << s))
			dk_time[s]++;

In mach table() syscall:

	ti.io_dkbusy = dk_busy;
	ti.io_ndrive = dk_ndrive;	// don't know any better
	
In bsd machine_table() syscall:

	ti.io_dkbusy = dk_busy;
	ti.io_ndrive = 0;
	for (i = 0; bus_dinit[i].bd_driver; i++)
		if (bus_dinit[i].bd_dk >= 0)
			ti.io_ndrive++;

Proposed IODiskDevice counters (all unsigned int's)
	readOps		
	bytesRead
	timeReading
	writeOps
	timeWriting
	bytesWritten
	
methods
	- (void)startRead;
	- (void)endRead : (int)bytesTransferred;
	- (void)startWrite;
	- (void)endWrite : (int)bytesTransferred;

..also, in kernel, current dk_XXX variables will be supported for a while.

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