xref: /src/sys/dev/raidframe/rf_reconstruct.c

/*	$NetBSD: rf_reconstruct.c,v 1.57 2003/12/29 02:38:18 oster Exp $	*/
/*
 * Copyright (c) 1995 Carnegie-Mellon University.
 * All rights reserved.
 *
 * Author: Mark Holland
 *
 * Permission to use, copy, modify and distribute this software and
 * its documentation is hereby granted, provided that both the copyright
 * notice and this permission notice appear in all copies of the
 * software, derivative works or modified versions, and any portions
 * thereof, and that both notices appear in supporting documentation.
 *
 * CARNEGIE MELLON ALLOWS FREE USE OF THIS SOFTWARE IN ITS "AS IS"
 * CONDITION.  CARNEGIE MELLON DISCLAIMS ANY LIABILITY OF ANY KIND
 * FOR ANY DAMAGES WHATSOEVER RESULTING FROM THE USE OF THIS SOFTWARE.
 *
 * Carnegie Mellon requests users of this software to return to
 *
 *  Software Distribution Coordinator  or  Software.Distribution (at) CS.CMU.EDU
 *  School of Computer Science
 *  Carnegie Mellon University
 *  Pittsburgh PA 15213-3890
 *
 * any improvements or extensions that they make and grant Carnegie the
 * rights to redistribute these changes.
 */

/************************************************************
 *
 * rf_reconstruct.c -- code to perform on-line reconstruction
 *
 ************************************************************/

#include <sys/cdefs.h>
__KERNEL_RCSID(0, "$NetBSD: rf_reconstruct.c,v 1.57 2003/12/29 02:38:18 oster Exp $");

#include <sys/time.h>
#include <sys/buf.h>
#include <sys/errno.h>

#include <sys/param.h>
#include <sys/systm.h>
#include <sys/proc.h>
#include <sys/ioctl.h>
#include <sys/fcntl.h>
#include <sys/vnode.h>
#include <dev/raidframe/raidframevar.h>

#include "rf_raid.h"
#include "rf_reconutil.h"
#include "rf_revent.h"
#include "rf_reconbuffer.h"
#include "rf_acctrace.h"
#include "rf_etimer.h"
#include "rf_dag.h"
#include "rf_desc.h"
#include "rf_debugprint.h"
#include "rf_general.h"
#include "rf_freelist.h"
#include "rf_driver.h"
#include "rf_utils.h"
#include "rf_shutdown.h"

#include "rf_kintf.h"

/* setting these to -1 causes them to be set to their default values if not set by debug options */

#if RF_DEBUG_RECON
#define Dprintf(s)         if (rf_reconDebug) rf_debug_printf(s,NULL,NULL,NULL,NULL,NULL,NULL,NULL,NULL)
#define Dprintf1(s,a)         if (rf_reconDebug) rf_debug_printf(s,(void *)((unsigned long)a),NULL,NULL,NULL,NULL,NULL,NULL,NULL)
#define Dprintf2(s,a,b)       if (rf_reconDebug) rf_debug_printf(s,(void *)((unsigned long)a),(void *)((unsigned long)b),NULL,NULL,NULL,NULL,NULL,NULL)
#define Dprintf3(s,a,b,c)     if (rf_reconDebug) rf_debug_printf(s,(void *)((unsigned long)a),(void *)((unsigned long)b),(void *)((unsigned long)c),NULL,NULL,NULL,NULL,NULL)
#define Dprintf4(s,a,b,c,d)   if (rf_reconDebug) rf_debug_printf(s,(void *)((unsigned long)a),(void *)((unsigned long)b),(void *)((unsigned long)c),(void *)((unsigned long)d),NULL,NULL,NULL,NULL)
#define Dprintf5(s,a,b,c,d,e) if (rf_reconDebug) rf_debug_printf(s,(void *)((unsigned long)a),(void *)((unsigned long)b),(void *)((unsigned long)c),(void *)((unsigned long)d),(void *)((unsigned long)e),NULL,NULL,NULL)
#define Dprintf6(s,a,b,c,d,e,f) if (rf_reconDebug) rf_debug_printf(s,(void *)((unsigned long)a),(void *)((unsigned long)b),(void *)((unsigned long)c),(void *)((unsigned long)d),(void *)((unsigned long)e),(void *)((unsigned long)f),NULL,NULL)
#define Dprintf7(s,a,b,c,d,e,f,g) if (rf_reconDebug) rf_debug_printf(s,(void *)((unsigned long)a),(void *)((unsigned long)b),(void *)((unsigned long)c),(void *)((unsigned long)d),(void *)((unsigned long)e),(void *)((unsigned long)f),(void *)((unsigned long)g),NULL)

#define DDprintf1(s,a)         if (rf_reconDebug) rf_debug_printf(s,(void *)((unsigned long)a),NULL,NULL,NULL,NULL,NULL,NULL,NULL)
#define DDprintf2(s,a,b)       if (rf_reconDebug) rf_debug_printf(s,(void *)((unsigned long)a),(void *)((unsigned long)b),NULL,NULL,NULL,NULL,NULL,NULL)

#else /* RF_DEBUG_RECON */

#define Dprintf(s) {}
#define Dprintf1(s,a) {}
#define Dprintf2(s,a,b) {}
#define Dprintf3(s,a,b,c) {}
#define Dprintf4(s,a,b,c,d) {}
#define Dprintf5(s,a,b,c,d,e) {}
#define Dprintf6(s,a,b,c,d,e,f) {}
#define Dprintf7(s,a,b,c,d,e,f,g) {}

#define DDprintf1(s,a) {}
#define DDprintf2(s,a,b) {}

#endif /* RF_DEBUG_RECON */


static RF_FreeList_t *rf_recond_freelist;
#define RF_MAX_FREE_RECOND  4
#define RF_RECOND_INC       1

static RF_RaidReconDesc_t *
AllocRaidReconDesc(RF_Raid_t * raidPtr,
    RF_RowCol_t col, RF_RaidDisk_t * spareDiskPtr,
    int numDisksDone, RF_RowCol_t scol);
static void FreeReconDesc(RF_RaidReconDesc_t * reconDesc);
static int
ProcessReconEvent(RF_Raid_t * raidPtr, RF_ReconEvent_t * event);
static int
IssueNextReadRequest(RF_Raid_t * raidPtr, RF_RowCol_t col);
static int TryToRead(RF_Raid_t * raidPtr, RF_RowCol_t col);
static int
ComputePSDiskOffsets(RF_Raid_t * raidPtr, RF_StripeNum_t psid,
    RF_RowCol_t col, RF_SectorNum_t * outDiskOffset,
    RF_SectorNum_t * outFailedDiskSectorOffset,
    RF_RowCol_t * spCol, RF_SectorNum_t * spOffset);
static int IssueNextWriteRequest(RF_Raid_t * raidPtr);
static int ReconReadDoneProc(void *arg, int status);
static int ReconWriteDoneProc(void *arg, int status);
static void
CheckForNewMinHeadSep(RF_Raid_t * raidPtr, RF_HeadSepLimit_t hsCtr);
static int
CheckHeadSeparation(RF_Raid_t * raidPtr, RF_PerDiskReconCtrl_t * ctrl,
    RF_RowCol_t col, RF_HeadSepLimit_t hsCtr,
    RF_ReconUnitNum_t which_ru);
static int
CheckForcedOrBlockedReconstruction(RF_Raid_t * raidPtr,
    RF_ReconParityStripeStatus_t * pssPtr, RF_PerDiskReconCtrl_t * ctrl,
    RF_RowCol_t col, RF_StripeNum_t psid,
    RF_ReconUnitNum_t which_ru);
static void ForceReconReadDoneProc(void *arg, int status);

static void rf_ShutdownReconstruction(void *);

struct RF_ReconDoneProc_s {
	void    (*proc) (RF_Raid_t *, void *);
	void   *arg;
	RF_ReconDoneProc_t *next;
};

static RF_FreeList_t *rf_rdp_freelist;
#define RF_MAX_FREE_RDP 4
#define RF_RDP_INC      1

static void
SignalReconDone(RF_Raid_t * raidPtr)
{
	RF_ReconDoneProc_t *p;

	RF_LOCK_MUTEX(raidPtr->recon_done_proc_mutex);
	for (p = raidPtr->recon_done_procs; p; p = p->next) {
		p->proc(raidPtr, p->arg);
	}
	RF_UNLOCK_MUTEX(raidPtr->recon_done_proc_mutex);
}

/**************************************************************************
 *
 * sets up the parameters that will be used by the reconstruction process
 * currently there are none, except for those that the layout-specific
 * configuration (e.g. rf_ConfigureDeclustered) routine sets up.
 *
 * in the kernel, we fire off the recon thread.
 *
 **************************************************************************/
static void
rf_ShutdownReconstruction(ignored)
	void   *ignored;
{
	RF_FREELIST_DESTROY(rf_recond_freelist, next, (RF_RaidReconDesc_t *));
	RF_FREELIST_DESTROY(rf_rdp_freelist, next, (RF_ReconDoneProc_t *));
}

int
rf_ConfigureReconstruction(listp)
	RF_ShutdownList_t **listp;
{
	int     rc;

	RF_FREELIST_CREATE(rf_recond_freelist, RF_MAX_FREE_RECOND,
	    RF_RECOND_INC, sizeof(RF_RaidReconDesc_t));
	if (rf_recond_freelist == NULL)
		return (ENOMEM);
	RF_FREELIST_CREATE(rf_rdp_freelist, RF_MAX_FREE_RDP,
	    RF_RDP_INC, sizeof(RF_ReconDoneProc_t));
	if (rf_rdp_freelist == NULL) {
		RF_FREELIST_DESTROY(rf_recond_freelist, next, (RF_RaidReconDesc_t *));
		return (ENOMEM);
	}
	rc = rf_ShutdownCreate(listp, rf_ShutdownReconstruction, NULL);
	if (rc) {
		rf_print_unable_to_add_shutdown(__FILE__, __LINE__, rc);
		rf_ShutdownReconstruction(NULL);
		return (rc);
	}
	return (0);
}

static RF_RaidReconDesc_t *
AllocRaidReconDesc(raidPtr, col, spareDiskPtr, numDisksDone, scol)
	RF_Raid_t *raidPtr;
	RF_RowCol_t col;
	RF_RaidDisk_t *spareDiskPtr;
	int     numDisksDone;
	RF_RowCol_t scol;
{

	RF_RaidReconDesc_t *reconDesc;

	RF_FREELIST_GET(rf_recond_freelist, reconDesc, next, (RF_RaidReconDesc_t *));

	reconDesc->raidPtr = raidPtr;
	reconDesc->col = col;
	reconDesc->spareDiskPtr = spareDiskPtr;
	reconDesc->numDisksDone = numDisksDone;
	reconDesc->scol = scol;
	reconDesc->state = 0;
	reconDesc->next = NULL;

	return (reconDesc);
}

static void
FreeReconDesc(reconDesc)
	RF_RaidReconDesc_t *reconDesc;
{
#if RF_RECON_STATS > 0
	printf("raid%d: %lu recon event waits, %lu recon delays\n",
	       reconDesc->raidPtr->raidid,
	       (long) reconDesc->numReconEventWaits,
	       (long) reconDesc->numReconExecDelays);
#endif				/* RF_RECON_STATS > 0 */
	printf("raid%d: %lu max exec ticks\n",
	       reconDesc->raidPtr->raidid,
	       (long) reconDesc->maxReconExecTicks);
#if (RF_RECON_STATS > 0) || defined(KERNEL)
	printf("\n");
#endif				/* (RF_RECON_STATS > 0) || KERNEL */
	RF_FREELIST_FREE(rf_recond_freelist, reconDesc, next);
}


/*****************************************************************************
 *
 * primary routine to reconstruct a failed disk.  This should be called from
 * within its own thread.  It won't return until reconstruction completes,
 * fails, or is aborted.
 *****************************************************************************/
int
rf_ReconstructFailedDisk(raidPtr, col)
	RF_Raid_t *raidPtr;
	RF_RowCol_t col;
{
	const RF_LayoutSW_t *lp;
	int     rc;

	lp = raidPtr->Layout.map;
	if (lp->SubmitReconBuffer) {
		/*
	         * The current infrastructure only supports reconstructing one
	         * disk at a time for each array.
	         */
		RF_LOCK_MUTEX(raidPtr->mutex);
		while (raidPtr->reconInProgress) {
			RF_WAIT_COND(raidPtr->waitForReconCond, raidPtr->mutex);
		}
		raidPtr->reconInProgress++;
		RF_UNLOCK_MUTEX(raidPtr->mutex);
		rc = rf_ReconstructFailedDiskBasic(raidPtr, col);
		RF_LOCK_MUTEX(raidPtr->mutex);
		raidPtr->reconInProgress--;
		RF_UNLOCK_MUTEX(raidPtr->mutex);
	} else {
		RF_ERRORMSG1("RECON: no way to reconstruct failed disk for arch %c\n",
		    lp->parityConfig);
		rc = EIO;
	}
	RF_SIGNAL_COND(raidPtr->waitForReconCond);
	return (rc);
}

int
rf_ReconstructFailedDiskBasic(raidPtr, col)
	RF_Raid_t *raidPtr;
	RF_RowCol_t col;
{
	RF_ComponentLabel_t c_label;
	RF_RaidDisk_t *spareDiskPtr = NULL;
	RF_RaidReconDesc_t *reconDesc;
	RF_RowCol_t scol;
	int     numDisksDone = 0, rc;

	/* first look for a spare drive onto which to reconstruct the data */
	/* spare disk descriptors are stored in row 0.  This may have to
	 * change eventually */

	RF_LOCK_MUTEX(raidPtr->mutex);
	RF_ASSERT(raidPtr->Disks[col].status == rf_ds_failed);

	if (raidPtr->Layout.map->flags & RF_DISTRIBUTE_SPARE) {
		if (raidPtr->status != rf_rs_degraded) {
			RF_ERRORMSG1("Unable to reconstruct disk at col %d because status not degraded\n", col);
			RF_UNLOCK_MUTEX(raidPtr->mutex);
			return (EINVAL);
		}
		scol = (-1);
	} else {
		for (scol = raidPtr->numCol; scol < raidPtr->numCol + raidPtr->numSpare; scol++) {
			if (raidPtr->Disks[scol].status == rf_ds_spare) {
				spareDiskPtr = &raidPtr->Disks[scol];
				spareDiskPtr->status = rf_ds_used_spare;
				break;
			}
		}
		if (!spareDiskPtr) {
			RF_ERRORMSG1("Unable to reconstruct disk at col %d because no spares are available\n", col);
			RF_UNLOCK_MUTEX(raidPtr->mutex);
			return (ENOSPC);
		}
		printf("RECON: initiating reconstruction on col %d -> spare at col %d\n", col, scol);
	}
	RF_UNLOCK_MUTEX(raidPtr->mutex);

	reconDesc = AllocRaidReconDesc((void *) raidPtr, col, spareDiskPtr, numDisksDone, scol);
	raidPtr->reconDesc = (void *) reconDesc;
#if RF_RECON_STATS > 0
	reconDesc->hsStallCount = 0;
	reconDesc->numReconExecDelays = 0;
	reconDesc->numReconEventWaits = 0;
#endif				/* RF_RECON_STATS > 0 */
	reconDesc->reconExecTimerRunning = 0;
	reconDesc->reconExecTicks = 0;
	reconDesc->maxReconExecTicks = 0;
	rc = rf_ContinueReconstructFailedDisk(reconDesc);

	if (!rc) {
		/* fix up the component label */
		/* Don't actually need the read here.. */
		raidread_component_label(
                        raidPtr->raid_cinfo[scol].ci_dev,
			raidPtr->raid_cinfo[scol].ci_vp,
			&c_label);

		raid_init_component_label( raidPtr, &c_label);
		c_label.row = 0;
		c_label.column = col;
		c_label.clean = RF_RAID_DIRTY;
		c_label.status = rf_ds_optimal;
		c_label.partitionSize = raidPtr->Disks[scol].partitionSize;

		/* We've just done a rebuild based on all the other
		   disks, so at this point the parity is known to be
		   clean, even if it wasn't before. */

		/* XXX doesn't hold for RAID 6!!*/

		RF_LOCK_MUTEX(raidPtr->mutex);
		raidPtr->parity_good = RF_RAID_CLEAN;
		RF_UNLOCK_MUTEX(raidPtr->mutex);

		/* XXXX MORE NEEDED HERE */

		raidwrite_component_label(
                        raidPtr->raid_cinfo[scol].ci_dev,
			raidPtr->raid_cinfo[scol].ci_vp,
			&c_label);


		rf_update_component_labels(raidPtr,
					   RF_NORMAL_COMPONENT_UPDATE);

	}
	return (rc);
}

/*

   Allow reconstructing a disk in-place -- i.e. component /dev/sd2e goes AWOL,
   and you don't get a spare until the next Monday.  With this function
   (and hot-swappable drives) you can now put your new disk containing
   /dev/sd2e on the bus, scsictl it alive, and then use raidctl(8) to
   rebuild the data "on the spot".

*/

int
rf_ReconstructInPlace(raidPtr, col)
	RF_Raid_t *raidPtr;
	RF_RowCol_t col;
{
	RF_RaidDisk_t *spareDiskPtr = NULL;
	RF_RaidReconDesc_t *reconDesc;
	const RF_LayoutSW_t *lp;
	RF_ComponentLabel_t c_label;
	int     numDisksDone = 0, rc;
	struct partinfo dpart;
	struct vnode *vp;
	struct vattr va;
	struct proc *proc;
	int retcode;
	int ac;

	lp = raidPtr->Layout.map;
	if (lp->SubmitReconBuffer) {
		/*
	         * The current infrastructure only supports reconstructing one
	         * disk at a time for each array.
	         */
		RF_LOCK_MUTEX(raidPtr->mutex);

		if (raidPtr->Disks[col].status != rf_ds_failed) {
			/* "It's gone..." */
			raidPtr->numFailures++;
			raidPtr->Disks[col].status = rf_ds_failed;
			raidPtr->status = rf_rs_degraded;
			RF_UNLOCK_MUTEX(raidPtr->mutex);
			rf_update_component_labels(raidPtr,
						   RF_NORMAL_COMPONENT_UPDATE);
			RF_LOCK_MUTEX(raidPtr->mutex);
		}

		while (raidPtr->reconInProgress) {
			RF_WAIT_COND(raidPtr->waitForReconCond, raidPtr->mutex);
		}

		raidPtr->reconInProgress++;


		/* first look for a spare drive onto which to reconstruct
		   the data.  spare disk descriptors are stored in row 0.
		   This may have to change eventually */

		/* Actually, we don't care if it's failed or not...
		   On a RAID set with correct parity, this function
		   should be callable on any component without ill affects. */
		/* RF_ASSERT(raidPtr->Disks[col].status == rf_ds_failed);
		 */

		if (raidPtr->Layout.map->flags & RF_DISTRIBUTE_SPARE) {
			RF_ERRORMSG1("Unable to reconstruct to disk at col %d: operation not supported for RF_DISTRIBUTE_SPARE\n", col);

			raidPtr->reconInProgress--;
			RF_UNLOCK_MUTEX(raidPtr->mutex);
			return (EINVAL);
		}

		proc = raidPtr->engine_thread;

		/* This device may have been opened successfully the
		   first time. Close it before trying to open it again.. */

		if (raidPtr->raid_cinfo[col].ci_vp != NULL) {
#if 0
			printf("Closed the open device: %s\n",
			       raidPtr->Disks[col].devname);
#endif
			vp = raidPtr->raid_cinfo[col].ci_vp;
			ac = raidPtr->Disks[col].auto_configured;
			RF_UNLOCK_MUTEX(raidPtr->mutex);
			rf_close_component(raidPtr, vp, ac);
			RF_LOCK_MUTEX(raidPtr->mutex);
			raidPtr->raid_cinfo[col].ci_vp = NULL;
		}
		/* note that this disk was *not* auto_configured (any longer)*/
		raidPtr->Disks[col].auto_configured = 0;

#if 0
		printf("About to (re-)open the device for rebuilding: %s\n",
		       raidPtr->Disks[col].devname);
#endif
		RF_UNLOCK_MUTEX(raidPtr->mutex);
		retcode = raidlookup(raidPtr->Disks[col].devname,
				     proc, &vp);

		if (retcode) {
			printf("raid%d: rebuilding: raidlookup on device: %s failed: %d!\n",raidPtr->raidid,
			       raidPtr->Disks[col].devname, retcode);

			/* the component isn't responding properly...
			   must be still dead :-( */
			RF_LOCK_MUTEX(raidPtr->mutex);
			raidPtr->reconInProgress--;
			RF_UNLOCK_MUTEX(raidPtr->mutex);
			return(retcode);

		} else {

			/* Ok, so we can at least do a lookup...
			   How about actually getting a vp for it? */

			if ((retcode = VOP_GETATTR(vp, &va, proc->p_ucred,
						   proc)) != 0) {
				RF_LOCK_MUTEX(raidPtr->mutex);
				raidPtr->reconInProgress--;
				RF_UNLOCK_MUTEX(raidPtr->mutex);
				return(retcode);
			}
			retcode = VOP_IOCTL(vp, DIOCGPART, &dpart,
					    FREAD, proc->p_ucred, proc);
			if (retcode) {
				RF_LOCK_MUTEX(raidPtr->mutex);
				raidPtr->reconInProgress--;
				RF_UNLOCK_MUTEX(raidPtr->mutex);
				return(retcode);
			}
			RF_LOCK_MUTEX(raidPtr->mutex);
			raidPtr->Disks[col].blockSize =
				dpart.disklab->d_secsize;

			raidPtr->Disks[col].numBlocks =
				dpart.part->p_size - rf_protectedSectors;

			raidPtr->raid_cinfo[col].ci_vp = vp;
			raidPtr->raid_cinfo[col].ci_dev = va.va_rdev;

			raidPtr->Disks[col].dev = va.va_rdev;

			/* we allow the user to specify that only a
			   fraction of the disks should be used this is
			   just for debug:  it speeds up
			 * the parity scan */
			raidPtr->Disks[col].numBlocks =
				raidPtr->Disks[col].numBlocks *
				rf_sizePercentage / 100;
			RF_UNLOCK_MUTEX(raidPtr->mutex);
		}



		spareDiskPtr = &raidPtr->Disks[col];
		spareDiskPtr->status = rf_ds_used_spare;

		printf("raid%d: initiating in-place reconstruction on column %d\n", raidPtr->raidid, col);

		reconDesc = AllocRaidReconDesc((void *) raidPtr, col,
					       spareDiskPtr, numDisksDone,
					       col);
		raidPtr->reconDesc = (void *) reconDesc;
#if RF_RECON_STATS > 0
		reconDesc->hsStallCount = 0;
		reconDesc->numReconExecDelays = 0;
		reconDesc->numReconEventWaits = 0;
#endif				/* RF_RECON_STATS > 0 */
		reconDesc->reconExecTimerRunning = 0;
		reconDesc->reconExecTicks = 0;
		reconDesc->maxReconExecTicks = 0;
		rc = rf_ContinueReconstructFailedDisk(reconDesc);

		RF_LOCK_MUTEX(raidPtr->mutex);
		raidPtr->reconInProgress--;
		RF_UNLOCK_MUTEX(raidPtr->mutex);

	} else {
		RF_ERRORMSG1("RECON: no way to reconstruct failed disk for arch %c\n",
			     lp->parityConfig);
		rc = EIO;
	}

	if (!rc) {
		RF_LOCK_MUTEX(raidPtr->mutex);
		/* Need to set these here, as at this point it'll be claiming
		   that the disk is in rf_ds_spared!  But we know better :-) */

		raidPtr->Disks[col].status = rf_ds_optimal;
		raidPtr->status = rf_rs_optimal;
		RF_UNLOCK_MUTEX(raidPtr->mutex);

		/* fix up the component label */
		/* Don't actually need the read here.. */
		raidread_component_label(raidPtr->raid_cinfo[col].ci_dev,
					 raidPtr->raid_cinfo[col].ci_vp,
					 &c_label);

		RF_LOCK_MUTEX(raidPtr->mutex);
		raid_init_component_label(raidPtr, &c_label);

		c_label.row = 0;
		c_label.column = col;

		/* We've just done a rebuild based on all the other
		   disks, so at this point the parity is known to be
		   clean, even if it wasn't before. */

		/* XXX doesn't hold for RAID 6!!*/

		raidPtr->parity_good = RF_RAID_CLEAN;
		RF_UNLOCK_MUTEX(raidPtr->mutex);

		raidwrite_component_label(raidPtr->raid_cinfo[col].ci_dev,
					  raidPtr->raid_cinfo[col].ci_vp,
					  &c_label);

		rf_update_component_labels(raidPtr,
					   RF_NORMAL_COMPONENT_UPDATE);

	}
	RF_SIGNAL_COND(raidPtr->waitForReconCond);
	return (rc);
}


int
rf_ContinueReconstructFailedDisk(reconDesc)
	RF_RaidReconDesc_t *reconDesc;
{
	RF_Raid_t *raidPtr = reconDesc->raidPtr;
	RF_RowCol_t col = reconDesc->col;
	RF_RowCol_t scol = reconDesc->scol;
	RF_ReconMap_t *mapPtr;
	RF_ReconCtrl_t *tmp_reconctrl;
	RF_ReconEvent_t *event;
	struct timeval etime, elpsd;
	unsigned long xor_s, xor_resid_us;
	int     i, ds;

	switch (reconDesc->state) {


	case 0:

		raidPtr->accumXorTimeUs = 0;

		/* create one trace record per physical disk */
		RF_Malloc(raidPtr->recon_tracerecs, raidPtr->numCol * sizeof(RF_AccTraceEntry_t), (RF_AccTraceEntry_t *));

		/* quiesce the array prior to starting recon.  this is needed
		 * to assure no nasty interactions with pending user writes.
		 * We need to do this before we change the disk or row status. */
		reconDesc->state = 1;

		Dprintf("RECON: begin request suspend\n");
		rf_SuspendNewRequestsAndWait(raidPtr);
		Dprintf("RECON: end request suspend\n");
		rf_StartUserStats(raidPtr);	/* zero out the stats kept on
						 * user accs */

		/* fall through to state 1 */

	case 1:

		/* allocate our RF_ReconCTRL_t before we protect raidPtr->reconControl[row] */
		tmp_reconctrl = rf_MakeReconControl(reconDesc, col, scol);

		RF_LOCK_MUTEX(raidPtr->mutex);

		/* create the reconstruction control pointer and install it in
		 * the right slot */
		raidPtr->reconControl = tmp_reconctrl;
		mapPtr = raidPtr->reconControl->reconMap;
		raidPtr->status = rf_rs_reconstructing;
		raidPtr->Disks[col].status = rf_ds_reconstructing;
		raidPtr->Disks[col].spareCol = scol;

		RF_UNLOCK_MUTEX(raidPtr->mutex);

		RF_GETTIME(raidPtr->reconControl->starttime);

		/* now start up the actual reconstruction: issue a read for
		 * each surviving disk */

		reconDesc->numDisksDone = 0;
		for (i = 0; i < raidPtr->numCol; i++) {
			if (i != col) {
				/* find and issue the next I/O on the
				 * indicated disk */
				if (IssueNextReadRequest(raidPtr, i)) {
					Dprintf1("RECON: done issuing for c%d\n", i);
					reconDesc->numDisksDone++;
				}
			}
		}

	case 2:
		Dprintf("RECON: resume requests\n");
		rf_ResumeNewRequests(raidPtr);


		reconDesc->state = 3;

	case 3:

		/* process reconstruction events until all disks report that
		 * they've completed all work */
		mapPtr = raidPtr->reconControl->reconMap;



		while (reconDesc->numDisksDone < raidPtr->numCol - 1) {

			event = rf_GetNextReconEvent(reconDesc, (void (*) (void *)) rf_ContinueReconstructFailedDisk, reconDesc);
			RF_ASSERT(event);

			if (ProcessReconEvent(raidPtr, event))
				reconDesc->numDisksDone++;
			raidPtr->reconControl->numRUsTotal =
				mapPtr->totalRUs;
			raidPtr->reconControl->numRUsComplete =
				mapPtr->totalRUs -
				rf_UnitsLeftToReconstruct(mapPtr);

			raidPtr->reconControl->percentComplete =
				(raidPtr->reconControl->numRUsComplete * 100 / raidPtr->reconControl->numRUsTotal);
#if RF_DEBUG_RECON
			if (rf_prReconSched) {
				rf_PrintReconSchedule(raidPtr->reconControl->reconMap, &(raidPtr->reconControl->starttime));
			}
#endif
		}



		reconDesc->state = 4;


	case 4:
		mapPtr = raidPtr->reconControl->reconMap;
		if (rf_reconDebug) {
			printf("RECON: all reads completed\n");
		}
		/* at this point all the reads have completed.  We now wait
		 * for any pending writes to complete, and then we're done */

		while (rf_UnitsLeftToReconstruct(raidPtr->reconControl->reconMap) > 0) {

			event = rf_GetNextReconEvent(reconDesc, (void (*) (void *)) rf_ContinueReconstructFailedDisk, reconDesc);
			RF_ASSERT(event);

			(void) ProcessReconEvent(raidPtr, event);	/* ignore return code */
			raidPtr->reconControl->percentComplete = 100 - (rf_UnitsLeftToReconstruct(mapPtr) * 100 / mapPtr->totalRUs);
#if RF_DEBUG_RECON
			if (rf_prReconSched) {
				rf_PrintReconSchedule(raidPtr->reconControl->reconMap, &(raidPtr->reconControl->starttime));
			}
#endif
		}
		reconDesc->state = 5;

	case 5:
		/* Success:  mark the dead disk as reconstructed.  We quiesce
		 * the array here to assure no nasty interactions with pending
		 * user accesses when we free up the psstatus structure as
		 * part of FreeReconControl() */

		reconDesc->state = 6;

		rf_SuspendNewRequestsAndWait(raidPtr);
		rf_StopUserStats(raidPtr);
		rf_PrintUserStats(raidPtr);	/* print out the stats on user
						 * accs accumulated during
						 * recon */

		/* fall through to state 6 */
	case 6:



		RF_LOCK_MUTEX(raidPtr->mutex);
		raidPtr->numFailures--;
		ds = (raidPtr->Layout.map->flags & RF_DISTRIBUTE_SPARE);
		raidPtr->Disks[col].status = (ds) ? rf_ds_dist_spared : rf_ds_spared;
		raidPtr->status = (ds) ? rf_rs_reconfigured : rf_rs_optimal;
		RF_UNLOCK_MUTEX(raidPtr->mutex);
		RF_GETTIME(etime);
		RF_TIMEVAL_DIFF(&(raidPtr->reconControl->starttime), &etime, &elpsd);

		/* XXX -- why is state 7 different from state 6 if there is no
		 * return() here? -- XXX Note that I set elpsd above & use it
		 * below, so if you put a return here you'll have to fix this.
		 * (also, FreeReconControl is called below) */

	case 7:

		rf_ResumeNewRequests(raidPtr);

		printf("raid%d: Reconstruction of disk at col %d completed\n",
		       raidPtr->raidid, col);
		xor_s = raidPtr->accumXorTimeUs / 1000000;
		xor_resid_us = raidPtr->accumXorTimeUs % 1000000;
		printf("raid%d: Recon time was %d.%06d seconds, accumulated XOR time was %ld us (%ld.%06ld)\n",
		       raidPtr->raidid,
		       (int) elpsd.tv_sec, (int) elpsd.tv_usec,
		       raidPtr->accumXorTimeUs, xor_s, xor_resid_us);
		printf("raid%d:  (start time %d sec %d usec, end time %d sec %d usec)\n",
		       raidPtr->raidid,
		       (int) raidPtr->reconControl->starttime.tv_sec,
		       (int) raidPtr->reconControl->starttime.tv_usec,
		       (int) etime.tv_sec, (int) etime.tv_usec);

#if RF_RECON_STATS > 0
		printf("raid%d: Total head-sep stall count was %d\n",
		       raidPtr->raidid, (int) reconDesc->hsStallCount);
#endif				/* RF_RECON_STATS > 0 */
		rf_FreeReconControl(raidPtr);
		RF_Free(raidPtr->recon_tracerecs, raidPtr->numCol * sizeof(RF_AccTraceEntry_t));
		FreeReconDesc(reconDesc);

	}

	SignalReconDone(raidPtr);
	return (0);
}
/*****************************************************************************
 * do the right thing upon each reconstruction event.
 * returns nonzero if and only if there is nothing left unread on the
 * indicated disk
 *****************************************************************************/
static int
ProcessReconEvent(raidPtr, event)
	RF_Raid_t *raidPtr;
	RF_ReconEvent_t *event;
{
	int     retcode = 0, submitblocked;
	RF_ReconBuffer_t *rbuf;
	RF_SectorCount_t sectorsPerRU;

	Dprintf1("RECON: ProcessReconEvent type %d\n", event->type);
	switch (event->type) {

		/* a read I/O has completed */
	case RF_REVENT_READDONE:
		rbuf = raidPtr->reconControl->perDiskInfo[event->col].rbuf;
		Dprintf2("RECON: READDONE EVENT: col %d psid %ld\n",
		    event->col, rbuf->parityStripeID);
		Dprintf7("RECON: done read  psid %ld buf %lx  %02x %02x %02x %02x %02x\n",
		    rbuf->parityStripeID, rbuf->buffer, rbuf->buffer[0] & 0xff, rbuf->buffer[1] & 0xff,
		    rbuf->buffer[2] & 0xff, rbuf->buffer[3] & 0xff, rbuf->buffer[4] & 0xff);
		rf_FreeDiskQueueData((RF_DiskQueueData_t *) rbuf->arg);
		submitblocked = rf_SubmitReconBuffer(rbuf, 0, 0);
		Dprintf1("RECON: submitblocked=%d\n", submitblocked);
		if (!submitblocked)
			retcode = IssueNextReadRequest(raidPtr, event->col);
		break;

		/* a write I/O has completed */
	case RF_REVENT_WRITEDONE:
#if RF_DEBUG_RECON
		if (rf_floatingRbufDebug) {
			rf_CheckFloatingRbufCount(raidPtr, 1);
		}
#endif
		sectorsPerRU = raidPtr->Layout.sectorsPerStripeUnit * raidPtr->Layout.SUsPerRU;
		rbuf = (RF_ReconBuffer_t *) event->arg;
		rf_FreeDiskQueueData((RF_DiskQueueData_t *) rbuf->arg);
		Dprintf3("RECON: WRITEDONE EVENT: psid %d ru %d (%d %% complete)\n",
		    rbuf->parityStripeID, rbuf->which_ru, raidPtr->reconControl->percentComplete);
		rf_ReconMapUpdate(raidPtr, raidPtr->reconControl->reconMap,
		    rbuf->failedDiskSectorOffset, rbuf->failedDiskSectorOffset + sectorsPerRU - 1);
		rf_RemoveFromActiveReconTable(raidPtr, rbuf->parityStripeID, rbuf->which_ru);

		if (rbuf->type == RF_RBUF_TYPE_FLOATING) {
			RF_LOCK_MUTEX(raidPtr->reconControl->rb_mutex);
			raidPtr->numFullReconBuffers--;
			rf_ReleaseFloatingReconBuffer(raidPtr, rbuf);
			RF_UNLOCK_MUTEX(raidPtr->reconControl->rb_mutex);
		} else
			if (rbuf->type == RF_RBUF_TYPE_FORCED)
				rf_FreeReconBuffer(rbuf);
			else
				RF_ASSERT(0);
		break;

	case RF_REVENT_BUFCLEAR:	/* A buffer-stall condition has been
					 * cleared */
		Dprintf1("RECON: BUFCLEAR EVENT: col %d\n", event->col);
		submitblocked = rf_SubmitReconBuffer(raidPtr->reconControl->perDiskInfo[event->col].rbuf, 0, (int) (long) event->arg);
		RF_ASSERT(!submitblocked);	/* we wouldn't have gotten the
						 * BUFCLEAR event if we
						 * couldn't submit */
		retcode = IssueNextReadRequest(raidPtr, event->col);
		break;

	case RF_REVENT_BLOCKCLEAR:	/* A user-write reconstruction
					 * blockage has been cleared */
		DDprintf1("RECON: BLOCKCLEAR EVENT: col %d\n", event->col);
		retcode = TryToRead(raidPtr, event->col);
		break;

	case RF_REVENT_HEADSEPCLEAR:	/* A max-head-separation
					 * reconstruction blockage has been
					 * cleared */
		Dprintf1("RECON: HEADSEPCLEAR EVENT: col %d\n", event->col);
		retcode = TryToRead(raidPtr, event->col);
		break;

		/* a buffer has become ready to write */
	case RF_REVENT_BUFREADY:
		Dprintf1("RECON: BUFREADY EVENT: col %d\n", event->col);
		retcode = IssueNextWriteRequest(raidPtr);
#if RF_DEBUG_RECON
		if (rf_floatingRbufDebug) {
			rf_CheckFloatingRbufCount(raidPtr, 1);
		}
#endif
		break;

		/* we need to skip the current RU entirely because it got
		 * recon'd while we were waiting for something else to happen */
	case RF_REVENT_SKIP:
		DDprintf1("RECON: SKIP EVENT: col %d\n", event->col);
		retcode = IssueNextReadRequest(raidPtr, event->col);
		break;

		/* a forced-reconstruction read access has completed.  Just
		 * submit the buffer */
	case RF_REVENT_FORCEDREADDONE:
		rbuf = (RF_ReconBuffer_t *) event->arg;
		rf_FreeDiskQueueData((RF_DiskQueueData_t *) rbuf->arg);
		DDprintf1("RECON: FORCEDREADDONE EVENT: col %d\n", event->col);
		submitblocked = rf_SubmitReconBuffer(rbuf, 1, 0);
		RF_ASSERT(!submitblocked);
		break;

	default:
		RF_PANIC();
	}
	rf_FreeReconEventDesc(event);
	return (retcode);
}
/*****************************************************************************
 *
 * find the next thing that's needed on the indicated disk, and issue
 * a read request for it.  We assume that the reconstruction buffer
 * associated with this process is free to receive the data.  If
 * reconstruction is blocked on the indicated RU, we issue a
 * blockage-release request instead of a physical disk read request.
 * If the current disk gets too far ahead of the others, we issue a
 * head-separation wait request and return.
 *
 * ctrl->{ru_count, curPSID, diskOffset} and
 * rbuf->failedDiskSectorOffset are maintained to point to the unit
 * we're currently accessing.  Note that this deviates from the
 * standard C idiom of having counters point to the next thing to be
 * accessed.  This allows us to easily retry when we're blocked by
 * head separation or reconstruction-blockage events.
 *
 * returns nonzero if and only if there is nothing left unread on the
 * indicated disk
 *
 *****************************************************************************/
static int
IssueNextReadRequest(raidPtr, col)
	RF_Raid_t *raidPtr;
	RF_RowCol_t col;
{
	RF_PerDiskReconCtrl_t *ctrl = &raidPtr->reconControl->perDiskInfo[col];
	RF_RaidLayout_t *layoutPtr = &raidPtr->Layout;
	RF_ReconBuffer_t *rbuf = ctrl->rbuf;
	RF_ReconUnitCount_t RUsPerPU = layoutPtr->SUsPerPU / layoutPtr->SUsPerRU;
	RF_SectorCount_t sectorsPerRU = layoutPtr->sectorsPerStripeUnit * layoutPtr->SUsPerRU;
	int     do_new_check = 0, retcode = 0, status;

	/* if we are currently the slowest disk, mark that we have to do a new
	 * check */
	if (ctrl->headSepCounter <= raidPtr->reconControl->minHeadSepCounter)
		do_new_check = 1;

	while (1) {

		ctrl->ru_count++;
		if (ctrl->ru_count < RUsPerPU) {
			ctrl->diskOffset += sectorsPerRU;
			rbuf->failedDiskSectorOffset += sectorsPerRU;
		} else {
			ctrl->curPSID++;
			ctrl->ru_count = 0;
			/* code left over from when head-sep was based on
			 * parity stripe id */
			if (ctrl->curPSID >= raidPtr->reconControl->lastPSID) {
				CheckForNewMinHeadSep(raidPtr, ++(ctrl->headSepCounter));
				return (1);	/* finito! */
			}
			/* find the disk offsets of the start of the parity
			 * stripe on both the current disk and the failed
			 * disk. skip this entire parity stripe if either disk
			 * does not appear in the indicated PS */
			status = ComputePSDiskOffsets(raidPtr, ctrl->curPSID, col, &ctrl->diskOffset, &rbuf->failedDiskSectorOffset,
			    &rbuf->spCol, &rbuf->spOffset);
			if (status) {
				ctrl->ru_count = RUsPerPU - 1;
				continue;
			}
		}
		rbuf->which_ru = ctrl->ru_count;

		/* skip this RU if it's already been reconstructed */
		if (rf_CheckRUReconstructed(raidPtr->reconControl->reconMap, rbuf->failedDiskSectorOffset)) {
			Dprintf2("Skipping psid %ld ru %d: already reconstructed\n", ctrl->curPSID, ctrl->ru_count);
			continue;
		}
		break;
	}
	ctrl->headSepCounter++;
	if (do_new_check)
		CheckForNewMinHeadSep(raidPtr, ctrl->headSepCounter);	/* update min if needed */


	/* at this point, we have definitely decided what to do, and we have
	 * only to see if we can actually do it now */
	rbuf->parityStripeID = ctrl->curPSID;
	rbuf->which_ru = ctrl->ru_count;
	memset((char *) &raidPtr->recon_tracerecs[col], 0,
	    sizeof(raidPtr->recon_tracerecs[col]));
	raidPtr->recon_tracerecs[col].reconacc = 1;
	RF_ETIMER_START(raidPtr->recon_tracerecs[col].recon_timer);
	retcode = TryToRead(raidPtr, col);
	return (retcode);
}

/*
 * tries to issue the next read on the indicated disk.  We may be
 * blocked by (a) the heads being too far apart, or (b) recon on the
 * indicated RU being blocked due to a write by a user thread.  In
 * this case, we issue a head-sep or blockage wait request, which will
 * cause this same routine to be invoked again later when the blockage
 * has cleared.
 */

static int
TryToRead(raidPtr, col)
	RF_Raid_t *raidPtr;
	RF_RowCol_t col;
{
	RF_PerDiskReconCtrl_t *ctrl = &raidPtr->reconControl->perDiskInfo[col];
	RF_SectorCount_t sectorsPerRU = raidPtr->Layout.sectorsPerStripeUnit * raidPtr->Layout.SUsPerRU;
	RF_StripeNum_t psid = ctrl->curPSID;
	RF_ReconUnitNum_t which_ru = ctrl->ru_count;
	RF_DiskQueueData_t *req;
	int     status, created = 0;
	RF_ReconParityStripeStatus_t *pssPtr;

	/* if the current disk is too far ahead of the others, issue a
	 * head-separation wait and return */
	if (CheckHeadSeparation(raidPtr, ctrl, col, ctrl->headSepCounter, which_ru))
		return (0);
	RF_LOCK_PSS_MUTEX(raidPtr, psid);
	pssPtr = rf_LookupRUStatus(raidPtr, raidPtr->reconControl->pssTable, psid, which_ru, RF_PSS_CREATE, &created);

	/* if recon is blocked on the indicated parity stripe, issue a
	 * block-wait request and return. this also must mark the indicated RU
	 * in the stripe as under reconstruction if not blocked. */
	status = CheckForcedOrBlockedReconstruction(raidPtr, pssPtr, ctrl, col, psid, which_ru);
	if (status == RF_PSS_RECON_BLOCKED) {
		Dprintf2("RECON: Stalling psid %ld ru %d: recon blocked\n", psid, which_ru);
		goto out;
	} else
		if (status == RF_PSS_FORCED_ON_WRITE) {
			rf_CauseReconEvent(raidPtr, col, NULL, RF_REVENT_SKIP);
			goto out;
		}
	/* make one last check to be sure that the indicated RU didn't get
	 * reconstructed while we were waiting for something else to happen.
	 * This is unfortunate in that it causes us to make this check twice
	 * in the normal case.  Might want to make some attempt to re-work
	 * this so that we only do this check if we've definitely blocked on
	 * one of the above checks.  When this condition is detected, we may
	 * have just created a bogus status entry, which we need to delete. */
	if (rf_CheckRUReconstructed(raidPtr->reconControl->reconMap, ctrl->rbuf->failedDiskSectorOffset)) {
		Dprintf2("RECON: Skipping psid %ld ru %d: prior recon after stall\n", psid, which_ru);
		if (created)
			rf_PSStatusDelete(raidPtr, raidPtr->reconControl->pssTable, pssPtr);
		rf_CauseReconEvent(raidPtr, col, NULL, RF_REVENT_SKIP);
		goto out;
	}
	/* found something to read.  issue the I/O */
	Dprintf4("RECON: Read for psid %ld on col %d offset %ld buf %lx\n",
	    psid, col, ctrl->diskOffset, ctrl->rbuf->buffer);
	RF_ETIMER_STOP(raidPtr->recon_tracerecs[col].recon_timer);
	RF_ETIMER_EVAL(raidPtr->recon_tracerecs[col].recon_timer);
	raidPtr->recon_tracerecs[col].specific.recon.recon_start_to_fetch_us =
	    RF_ETIMER_VAL_US(raidPtr->recon_tracerecs[col].recon_timer);
	RF_ETIMER_START(raidPtr->recon_tracerecs[col].recon_timer);

	/* should be ok to use a NULL proc pointer here, all the bufs we use
	 * should be in kernel space */
	req = rf_CreateDiskQueueData(RF_IO_TYPE_READ, ctrl->diskOffset, sectorsPerRU, ctrl->rbuf->buffer, psid, which_ru,
	    ReconReadDoneProc, (void *) ctrl, NULL, &raidPtr->recon_tracerecs[col], (void *) raidPtr, 0, NULL);

	RF_ASSERT(req);		/* XXX -- fix this -- XXX */

	ctrl->rbuf->arg = (void *) req;
	rf_DiskIOEnqueue(&raidPtr->Queues[col], req, RF_IO_RECON_PRIORITY);
	pssPtr->issued[col] = 1;

out:
	RF_UNLOCK_PSS_MUTEX(raidPtr, psid);
	return (0);
}


/*
 * given a parity stripe ID, we want to find out whether both the
 * current disk and the failed disk exist in that parity stripe.  If
 * not, we want to skip this whole PS.  If so, we want to find the
 * disk offset of the start of the PS on both the current disk and the
 * failed disk.
 *
 * this works by getting a list of disks comprising the indicated
 * parity stripe, and searching the list for the current and failed
 * disks.  Once we've decided they both exist in the parity stripe, we
 * need to decide whether each is data or parity, so that we'll know
 * which mapping function to call to get the corresponding disk
 * offsets.
 *
 * this is kind of unpleasant, but doing it this way allows the
 * reconstruction code to use parity stripe IDs rather than physical
 * disks address to march through the failed disk, which greatly
 * simplifies a lot of code, as well as eliminating the need for a
 * reverse-mapping function.  I also think it will execute faster,
 * since the calls to the mapping module are kept to a minimum.
 *
 * ASSUMES THAT THE STRIPE IDENTIFIER IDENTIFIES THE DISKS COMPRISING
 * THE STRIPE IN THE CORRECT ORDER */


static int
ComputePSDiskOffsets(
    RF_Raid_t * raidPtr,	/* raid descriptor */
    RF_StripeNum_t psid,	/* parity stripe identifier */
    RF_RowCol_t col,            /* column of disk to find the offsets for */
    RF_SectorNum_t * outDiskOffset,
    RF_SectorNum_t * outFailedDiskSectorOffset,
    RF_RowCol_t * spCol,        /* OUT: col of spare unit for failed unit */
    RF_SectorNum_t * spOffset)
{				/* OUT: offset into disk containing spare unit */
	RF_RaidLayout_t *layoutPtr = &raidPtr->Layout;
	RF_RowCol_t fcol = raidPtr->reconControl->fcol;
	RF_RaidAddr_t sosRaidAddress;	/* start-of-stripe */
	RF_RowCol_t *diskids;
	u_int   i, j, k, i_offset, j_offset;
	RF_RowCol_t pcol;
	int     testcol;
	RF_SectorNum_t poffset;
	char    i_is_parity = 0, j_is_parity = 0;
	RF_RowCol_t stripeWidth = layoutPtr->numDataCol + layoutPtr->numParityCol;

	/* get a listing of the disks comprising that stripe */
	sosRaidAddress = rf_ParityStripeIDToRaidAddress(layoutPtr, psid);
	(layoutPtr->map->IdentifyStripe) (raidPtr, sosRaidAddress, &diskids);
	RF_ASSERT(diskids);

	/* reject this entire parity stripe if it does not contain the
	 * indicated disk or it does not contain the failed disk */

	for (i = 0; i < stripeWidth; i++) {
		if (col == diskids[i])
			break;
	}
	if (i == stripeWidth)
		goto skipit;
	for (j = 0; j < stripeWidth; j++) {
		if (fcol == diskids[j])
			break;
	}
	if (j == stripeWidth) {
		goto skipit;
	}
	/* find out which disk the parity is on */
	(layoutPtr->map->MapParity) (raidPtr, sosRaidAddress, &pcol, &poffset, RF_DONT_REMAP);

	/* find out if either the current RU or the failed RU is parity */
	/* also, if the parity occurs in this stripe prior to the data and/or
	 * failed col, we need to decrement i and/or j */
	for (k = 0; k < stripeWidth; k++)
		if (diskids[k] == pcol)
			break;
	RF_ASSERT(k < stripeWidth);
	i_offset = i;
	j_offset = j;
	if (k < i)
		i_offset--;
	else
		if (k == i) {
			i_is_parity = 1;
			i_offset = 0;
		}		/* set offsets to zero to disable multiply
				 * below */
	if (k < j)
		j_offset--;
	else
		if (k == j) {
			j_is_parity = 1;
			j_offset = 0;
		}
	/* at this point, [ij]_is_parity tells us whether the [current,failed]
	 * disk is parity at the start of this RU, and, if data, "[ij]_offset"
	 * tells us how far into the stripe the [current,failed] disk is. */

	/* call the mapping routine to get the offset into the current disk,
	 * repeat for failed disk. */
	if (i_is_parity)
		layoutPtr->map->MapParity(raidPtr, sosRaidAddress + i_offset * layoutPtr->sectorsPerStripeUnit, &testcol, outDiskOffset, RF_DONT_REMAP);
	else
		layoutPtr->map->MapSector(raidPtr, sosRaidAddress + i_offset * layoutPtr->sectorsPerStripeUnit, &testcol, outDiskOffset, RF_DONT_REMAP);

	RF_ASSERT(col == testcol);

	if (j_is_parity)
		layoutPtr->map->MapParity(raidPtr, sosRaidAddress + j_offset * layoutPtr->sectorsPerStripeUnit, &testcol, outFailedDiskSectorOffset, RF_DONT_REMAP);
	else
		layoutPtr->map->MapSector(raidPtr, sosRaidAddress + j_offset * layoutPtr->sectorsPerStripeUnit, &testcol, outFailedDiskSectorOffset, RF_DONT_REMAP);
	RF_ASSERT(fcol == testcol);

	/* now locate the spare unit for the failed unit */
	if (layoutPtr->map->flags & RF_DISTRIBUTE_SPARE) {
		if (j_is_parity)
			layoutPtr->map->MapParity(raidPtr, sosRaidAddress + j_offset * layoutPtr->sectorsPerStripeUnit, spCol, spOffset, RF_REMAP);
		else
			layoutPtr->map->MapSector(raidPtr, sosRaidAddress + j_offset * layoutPtr->sectorsPerStripeUnit, spCol, spOffset, RF_REMAP);
	} else {
		*spCol = raidPtr->reconControl->spareCol;
		*spOffset = *outFailedDiskSectorOffset;
	}

	return (0);

skipit:
	Dprintf2("RECON: Skipping psid %ld: nothing needed from r%d c%d\n",
	    psid, col);
	return (1);
}
/* this is called when a buffer has become ready to write to the replacement disk */
static int
IssueNextWriteRequest(raidPtr)
	RF_Raid_t *raidPtr;
{
	RF_RaidLayout_t *layoutPtr = &raidPtr->Layout;
	RF_SectorCount_t sectorsPerRU = layoutPtr->sectorsPerStripeUnit * layoutPtr->SUsPerRU;
	RF_RowCol_t fcol = raidPtr->reconControl->fcol;
	RF_ReconBuffer_t *rbuf;
	RF_DiskQueueData_t *req;

	rbuf = rf_GetFullReconBuffer(raidPtr->reconControl);
	RF_ASSERT(rbuf);	/* there must be one available, or we wouldn't
				 * have gotten the event that sent us here */
	RF_ASSERT(rbuf->pssPtr);

	rbuf->pssPtr->writeRbuf = rbuf;
	rbuf->pssPtr = NULL;

	Dprintf6("RECON: New write (c %d offs %d) for psid %ld ru %d (failed disk offset %ld) buf %lx\n",
	    rbuf->spCol, rbuf->spOffset, rbuf->parityStripeID,
	    rbuf->which_ru, rbuf->failedDiskSectorOffset, rbuf->buffer);
	Dprintf6("RECON: new write psid %ld   %02x %02x %02x %02x %02x\n",
	    rbuf->parityStripeID, rbuf->buffer[0] & 0xff, rbuf->buffer[1] & 0xff,
	    rbuf->buffer[2] & 0xff, rbuf->buffer[3] & 0xff, rbuf->buffer[4] & 0xff);

	/* should be ok to use a NULL b_proc here b/c all addrs should be in
	 * kernel space */
	req = rf_CreateDiskQueueData(RF_IO_TYPE_WRITE, rbuf->spOffset,
	    sectorsPerRU, rbuf->buffer,
	    rbuf->parityStripeID, rbuf->which_ru,
	    ReconWriteDoneProc, (void *) rbuf, NULL,
	    &raidPtr->recon_tracerecs[fcol],
	    (void *) raidPtr, 0, NULL);

	RF_ASSERT(req);		/* XXX -- fix this -- XXX */

	rbuf->arg = (void *) req;
	rf_DiskIOEnqueue(&raidPtr->Queues[rbuf->spCol], req, RF_IO_RECON_PRIORITY);

	return (0);
}

/*
 * this gets called upon the completion of a reconstruction read
 * operation the arg is a pointer to the per-disk reconstruction
 * control structure for the process that just finished a read.
 *
 * called at interrupt context in the kernel, so don't do anything
 * illegal here.
 */
static int
ReconReadDoneProc(arg, status)
	void   *arg;
	int     status;
{
	RF_PerDiskReconCtrl_t *ctrl = (RF_PerDiskReconCtrl_t *) arg;
	RF_Raid_t *raidPtr = ctrl->reconCtrl->reconDesc->raidPtr;

	if (status) {
		/*
	         * XXX
	         */
		printf("Recon read failed!\n");
		RF_PANIC();
	}
	RF_ETIMER_STOP(raidPtr->recon_tracerecs[ctrl->col].recon_timer);
	RF_ETIMER_EVAL(raidPtr->recon_tracerecs[ctrl->col].recon_timer);
	raidPtr->recon_tracerecs[ctrl->col].specific.recon.recon_fetch_to_return_us =
	    RF_ETIMER_VAL_US(raidPtr->recon_tracerecs[ctrl->col].recon_timer);
	RF_ETIMER_START(raidPtr->recon_tracerecs[ctrl->col].recon_timer);

	rf_CauseReconEvent(raidPtr, ctrl->col, NULL, RF_REVENT_READDONE);
	return (0);
}
/* this gets called upon the completion of a reconstruction write operation.
 * the arg is a pointer to the rbuf that was just written
 *
 * called at interrupt context in the kernel, so don't do anything illegal here.
 */
static int
ReconWriteDoneProc(arg, status)
	void   *arg;
	int     status;
{
	RF_ReconBuffer_t *rbuf = (RF_ReconBuffer_t *) arg;

	Dprintf2("Reconstruction completed on psid %ld ru %d\n", rbuf->parityStripeID, rbuf->which_ru);
	if (status) {
		printf("Recon write failed!\n");	/* fprintf(stderr,"Recon
							 * write failed!\n"); */
		RF_PANIC();
	}
	rf_CauseReconEvent((RF_Raid_t *) rbuf->raidPtr, rbuf->col, arg, RF_REVENT_WRITEDONE);
	return (0);
}


/*
 * computes a new minimum head sep, and wakes up anyone who needs to
 * be woken as a result
 */
static void
CheckForNewMinHeadSep(raidPtr, hsCtr)
	RF_Raid_t *raidPtr;
	RF_HeadSepLimit_t hsCtr;
{
	RF_ReconCtrl_t *reconCtrlPtr = raidPtr->reconControl;
	RF_HeadSepLimit_t new_min;
	RF_RowCol_t i;
	RF_CallbackDesc_t *p;
	RF_ASSERT(hsCtr >= reconCtrlPtr->minHeadSepCounter);	/* from the definition
								 * of a minimum */


	RF_LOCK_MUTEX(reconCtrlPtr->rb_mutex);

	new_min = ~(1L << (8 * sizeof(long) - 1));	/* 0x7FFF....FFF */
	for (i = 0; i < raidPtr->numCol; i++)
		if (i != reconCtrlPtr->fcol) {
			if (reconCtrlPtr->perDiskInfo[i].headSepCounter < new_min)
				new_min = reconCtrlPtr->perDiskInfo[i].headSepCounter;
		}
	/* set the new minimum and wake up anyone who can now run again */
	if (new_min != reconCtrlPtr->minHeadSepCounter) {
		reconCtrlPtr->minHeadSepCounter = new_min;
		Dprintf1("RECON:  new min head pos counter val is %ld\n", new_min);
		while (reconCtrlPtr->headSepCBList) {
			if (reconCtrlPtr->headSepCBList->callbackArg.v > new_min)
				break;
			p = reconCtrlPtr->headSepCBList;
			reconCtrlPtr->headSepCBList = p->next;
			p->next = NULL;
			rf_CauseReconEvent(raidPtr, p->col, NULL, RF_REVENT_HEADSEPCLEAR);
			rf_FreeCallbackDesc(p);
		}

	}
	RF_UNLOCK_MUTEX(reconCtrlPtr->rb_mutex);
}

/*
 * checks to see that the maximum head separation will not be violated
 * if we initiate a reconstruction I/O on the indicated disk.
 * Limiting the maximum head separation between two disks eliminates
 * the nasty buffer-stall conditions that occur when one disk races
 * ahead of the others and consumes all of the floating recon buffers.
 * This code is complex and unpleasant but it's necessary to avoid
 * some very nasty, albeit fairly rare, reconstruction behavior.
 *
 * returns non-zero if and only if we have to stop working on the
 * indicated disk due to a head-separation delay.
 */
static int
CheckHeadSeparation(
    RF_Raid_t * raidPtr,
    RF_PerDiskReconCtrl_t * ctrl,
    RF_RowCol_t col,
    RF_HeadSepLimit_t hsCtr,
    RF_ReconUnitNum_t which_ru)
{
	RF_ReconCtrl_t *reconCtrlPtr = raidPtr->reconControl;
	RF_CallbackDesc_t *cb, *p, *pt;
	int     retval = 0;

	/* if we're too far ahead of the slowest disk, stop working on this
	 * disk until the slower ones catch up.  We do this by scheduling a
	 * wakeup callback for the time when the slowest disk has caught up.
	 * We define "caught up" with 20% hysteresis, i.e. the head separation
	 * must have fallen to at most 80% of the max allowable head
	 * separation before we'll wake up.
	 *
	 */
	RF_LOCK_MUTEX(reconCtrlPtr->rb_mutex);
	if ((raidPtr->headSepLimit >= 0) &&
	    ((ctrl->headSepCounter - reconCtrlPtr->minHeadSepCounter) > raidPtr->headSepLimit)) {
		Dprintf5("raid%d: RECON: head sep stall: col %d hsCtr %ld minHSCtr %ld limit %ld\n",
			 raidPtr->raidid, col, ctrl->headSepCounter,
			 reconCtrlPtr->minHeadSepCounter,
			 raidPtr->headSepLimit);
		cb = rf_AllocCallbackDesc();
		/* the minHeadSepCounter value we have to get to before we'll
		 * wake up.  build in 20% hysteresis. */
		cb->callbackArg.v = (ctrl->headSepCounter - raidPtr->headSepLimit + raidPtr->headSepLimit / 5);
		cb->col = col;
		cb->next = NULL;

		/* insert this callback descriptor into the sorted list of
		 * pending head-sep callbacks */
		p = reconCtrlPtr->headSepCBList;
		if (!p)
			reconCtrlPtr->headSepCBList = cb;
		else
			if (cb->callbackArg.v < p->callbackArg.v) {
				cb->next = reconCtrlPtr->headSepCBList;
				reconCtrlPtr->headSepCBList = cb;
			} else {
				for (pt = p, p = p->next; p && (p->callbackArg.v < cb->callbackArg.v); pt = p, p = p->next);
				cb->next = p;
				pt->next = cb;
			}
		retval = 1;
#if RF_RECON_STATS > 0
		ctrl->reconCtrl->reconDesc->hsStallCount++;
#endif				/* RF_RECON_STATS > 0 */
	}
	RF_UNLOCK_MUTEX(reconCtrlPtr->rb_mutex);

	return (retval);
}
/*
 * checks to see if reconstruction has been either forced or blocked
 * by a user operation.  if forced, we skip this RU entirely.  else if
 * blocked, put ourselves on the wait list.  else return 0.
 *
 * ASSUMES THE PSS MUTEX IS LOCKED UPON ENTRY
 */
static int
CheckForcedOrBlockedReconstruction(
    RF_Raid_t * raidPtr,
    RF_ReconParityStripeStatus_t * pssPtr,
    RF_PerDiskReconCtrl_t * ctrl,
    RF_RowCol_t col,
    RF_StripeNum_t psid,
    RF_ReconUnitNum_t which_ru)
{
	RF_CallbackDesc_t *cb;
	int     retcode = 0;

	if ((pssPtr->flags & RF_PSS_FORCED_ON_READ) || (pssPtr->flags & RF_PSS_FORCED_ON_WRITE))
		retcode = RF_PSS_FORCED_ON_WRITE;
	else
		if (pssPtr->flags & RF_PSS_RECON_BLOCKED) {
			Dprintf3("RECON: col %d blocked at psid %ld ru %d\n", col, psid, which_ru);
			cb = rf_AllocCallbackDesc();	/* append ourselves to
							 * the blockage-wait
							 * list */
			cb->col = col;
			cb->next = pssPtr->blockWaitList;
			pssPtr->blockWaitList = cb;
			retcode = RF_PSS_RECON_BLOCKED;
		}
	if (!retcode)
		pssPtr->flags |= RF_PSS_UNDER_RECON;	/* mark this RU as under
							 * reconstruction */

	return (retcode);
}
/*
 * if reconstruction is currently ongoing for the indicated stripeID,
 * reconstruction is forced to completion and we return non-zero to
 * indicate that the caller must wait.  If not, then reconstruction is
 * blocked on the indicated stripe and the routine returns zero.  If
 * and only if we return non-zero, we'll cause the cbFunc to get
 * invoked with the cbArg when the reconstruction has completed.
 */
int
rf_ForceOrBlockRecon(raidPtr, asmap, cbFunc, cbArg)
	RF_Raid_t *raidPtr;
	RF_AccessStripeMap_t *asmap;
	void    (*cbFunc) (RF_Raid_t *, void *);
	void   *cbArg;
{
	RF_StripeNum_t stripeID = asmap->stripeID;	/* the stripe ID we're
							 * forcing recon on */
	RF_SectorCount_t sectorsPerRU = raidPtr->Layout.sectorsPerStripeUnit * raidPtr->Layout.SUsPerRU;	/* num sects in one RU */
	RF_ReconParityStripeStatus_t *pssPtr;	/* a pointer to the parity
						 * stripe status structure */
	RF_StripeNum_t psid;	/* parity stripe id */
	RF_SectorNum_t offset, fd_offset;	/* disk offset, failed-disk
						 * offset */
	RF_RowCol_t *diskids;
	RF_ReconUnitNum_t which_ru;	/* RU within parity stripe */
	RF_RowCol_t fcol, diskno, i;
	RF_ReconBuffer_t *new_rbuf;	/* ptr to newly allocated rbufs */
	RF_DiskQueueData_t *req;/* disk I/O req to be enqueued */
	RF_CallbackDesc_t *cb;
	int     created = 0, nPromoted;

	psid = rf_MapStripeIDToParityStripeID(&raidPtr->Layout, stripeID, &which_ru);

	RF_LOCK_PSS_MUTEX(raidPtr, psid);

	pssPtr = rf_LookupRUStatus(raidPtr, raidPtr->reconControl->pssTable, psid, which_ru, RF_PSS_CREATE | RF_PSS_RECON_BLOCKED, &created);

	/* if recon is not ongoing on this PS, just return */
	if (!(pssPtr->flags & RF_PSS_UNDER_RECON)) {
		RF_UNLOCK_PSS_MUTEX(raidPtr, psid);
		return (0);
	}
	/* otherwise, we have to wait for reconstruction to complete on this
	 * RU. */
	/* In order to avoid waiting for a potentially large number of
	 * low-priority accesses to complete, we force a normal-priority (i.e.
	 * not low-priority) reconstruction on this RU. */
	if (!(pssPtr->flags & RF_PSS_FORCED_ON_WRITE) && !(pssPtr->flags & RF_PSS_FORCED_ON_READ)) {
		DDprintf1("Forcing recon on psid %ld\n", psid);
		pssPtr->flags |= RF_PSS_FORCED_ON_WRITE;	/* mark this RU as under
								 * forced recon */
		pssPtr->flags &= ~RF_PSS_RECON_BLOCKED;	/* clear the blockage
							 * that we just set */
		fcol = raidPtr->reconControl->fcol;

		/* get a listing of the disks comprising the indicated stripe */
		(raidPtr->Layout.map->IdentifyStripe) (raidPtr, asmap->raidAddress, &diskids);

		/* For previously issued reads, elevate them to normal
		 * priority.  If the I/O has already completed, it won't be
		 * found in the queue, and hence this will be a no-op. For
		 * unissued reads, allocate buffers and issue new reads.  The
		 * fact that we've set the FORCED bit means that the regular
		 * recon procs will not re-issue these reqs */
		for (i = 0; i < raidPtr->Layout.numDataCol + raidPtr->Layout.numParityCol; i++)
			if ((diskno = diskids[i]) != fcol) {
				if (pssPtr->issued[diskno]) {
					nPromoted = rf_DiskIOPromote(&raidPtr->Queues[diskno], psid, which_ru);
					if (rf_reconDebug && nPromoted)
						printf("raid%d: promoted read from col %d\n", raidPtr->raidid, diskno);
				} else {
					new_rbuf = rf_MakeReconBuffer(raidPtr, diskno, RF_RBUF_TYPE_FORCED);	/* create new buf */
					ComputePSDiskOffsets(raidPtr, psid, diskno, &offset, &fd_offset,
					    &new_rbuf->spCol, &new_rbuf->spOffset);	/* find offsets & spare
													 * location */
					new_rbuf->parityStripeID = psid;	/* fill in the buffer */
					new_rbuf->which_ru = which_ru;
					new_rbuf->failedDiskSectorOffset = fd_offset;
					new_rbuf->priority = RF_IO_NORMAL_PRIORITY;

					/* use NULL b_proc b/c all addrs
					 * should be in kernel space */
					req = rf_CreateDiskQueueData(RF_IO_TYPE_READ, offset + which_ru * sectorsPerRU, sectorsPerRU, new_rbuf->buffer,
					    psid, which_ru, (int (*) (void *, int)) ForceReconReadDoneProc, (void *) new_rbuf, NULL,
					    NULL, (void *) raidPtr, 0, NULL);

					RF_ASSERT(req);	/* XXX -- fix this --
							 * XXX */

					new_rbuf->arg = req;
					rf_DiskIOEnqueue(&raidPtr->Queues[diskno], req, RF_IO_NORMAL_PRIORITY);	/* enqueue the I/O */
					Dprintf2("raid%d: Issued new read req on col %d\n", raidPtr->raidid, diskno);
				}
			}
		/* if the write is sitting in the disk queue, elevate its
		 * priority */
		if (rf_DiskIOPromote(&raidPtr->Queues[fcol], psid, which_ru))
			printf("raid%d: promoted write to col %d\n",
			       raidPtr->raidid, fcol);
	}
	/* install a callback descriptor to be invoked when recon completes on
	 * this parity stripe. */
	cb = rf_AllocCallbackDesc();
	/* XXX the following is bogus.. These functions don't really match!!
	 * GO */
	cb->callbackFunc = (void (*) (RF_CBParam_t)) cbFunc;
	cb->callbackArg.p = (void *) cbArg;
	cb->next = pssPtr->procWaitList;
	pssPtr->procWaitList = cb;
	DDprintf2("raid%d: Waiting for forced recon on psid %ld\n",
		  raidPtr->raidid, psid);

	RF_UNLOCK_PSS_MUTEX(raidPtr, psid);
	return (1);
}
/* called upon the completion of a forced reconstruction read.
 * all we do is schedule the FORCEDREADONE event.
 * called at interrupt context in the kernel, so don't do anything illegal here.
 */
static void
ForceReconReadDoneProc(arg, status)
	void   *arg;
	int     status;
{
	RF_ReconBuffer_t *rbuf = arg;

	if (status) {
		printf("Forced recon read failed!\n");	/* fprintf(stderr,"Forced
							 *  recon read
							 * failed!\n"); */
		RF_PANIC();
	}
	rf_CauseReconEvent((RF_Raid_t *) rbuf->raidPtr, rbuf->col, (void *) rbuf, RF_REVENT_FORCEDREADDONE);
}
/* releases a block on the reconstruction of the indicated stripe */
int
rf_UnblockRecon(raidPtr, asmap)
	RF_Raid_t *raidPtr;
	RF_AccessStripeMap_t *asmap;
{
	RF_StripeNum_t stripeID = asmap->stripeID;
	RF_ReconParityStripeStatus_t *pssPtr;
	RF_ReconUnitNum_t which_ru;
	RF_StripeNum_t psid;
	int     created = 0;
	RF_CallbackDesc_t *cb;

	psid = rf_MapStripeIDToParityStripeID(&raidPtr->Layout, stripeID, &which_ru);
	RF_LOCK_PSS_MUTEX(raidPtr, psid);
	pssPtr = rf_LookupRUStatus(raidPtr, raidPtr->reconControl->pssTable, psid, which_ru, RF_PSS_NONE, &created);

	/* When recon is forced, the pss desc can get deleted before we get
	 * back to unblock recon. But, this can _only_ happen when recon is
	 * forced. It would be good to put some kind of sanity check here, but
	 * how to decide if recon was just forced or not? */
	if (!pssPtr) {
		/* printf("Warning: no pss descriptor upon unblock on psid %ld
		 * RU %d\n",psid,which_ru); */
#if (RF_DEBUG_RECON > 0) || (RF_DEBUG_PSS > 0)
		if (rf_reconDebug || rf_pssDebug)
			printf("Warning: no pss descriptor upon unblock on psid %ld RU %d\n", (long) psid, which_ru);
#endif
		goto out;
	}
	pssPtr->blockCount--;
	Dprintf3("raid%d: unblocking recon on psid %ld: blockcount is %d\n",
		 raidPtr->raidid, psid, pssPtr->blockCount);
	if (pssPtr->blockCount == 0) {	/* if recon blockage has been released */

		/* unblock recon before calling CauseReconEvent in case
		 * CauseReconEvent causes us to try to issue a new read before
		 * returning here. */
		pssPtr->flags &= ~RF_PSS_RECON_BLOCKED;


		while (pssPtr->blockWaitList) {
			/* spin through the block-wait list and
			   release all the waiters */
			cb = pssPtr->blockWaitList;
			pssPtr->blockWaitList = cb->next;
			cb->next = NULL;
			rf_CauseReconEvent(raidPtr, cb->col, NULL, RF_REVENT_BLOCKCLEAR);
			rf_FreeCallbackDesc(cb);
		}
		if (!(pssPtr->flags & RF_PSS_UNDER_RECON)) {
			/* if no recon was requested while recon was blocked */
			rf_PSStatusDelete(raidPtr, raidPtr->reconControl->pssTable, pssPtr);
		}
	}
out:
	RF_UNLOCK_PSS_MUTEX(raidPtr, psid);
	return (0);
}