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

/*	$NetBSD: rf_reconstruct.c,v 1.104 2008/05/19 19:49:54 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 1.104 2008/05/19 19:49:54 oster Exp $");

#include <sys/param.h>
#include <sys/time.h>
#include <sys/buf.h>
#include <sys/errno.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_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 */

#define RF_RECON_DONE_READS   1
#define RF_RECON_READ_ERROR   2
#define RF_RECON_WRITE_ERROR  3
#define RF_RECON_READ_STOPPED 4
#define RF_RECON_WRITE_DONE   5

#define RF_MAX_FREE_RECONBUFFER 32
#define RF_MIN_FREE_RECONBUFFER 16

static RF_RaidReconDesc_t *AllocRaidReconDesc(RF_Raid_t *, RF_RowCol_t,
					      RF_RaidDisk_t *, int, RF_RowCol_t);
static void FreeReconDesc(RF_RaidReconDesc_t *);
static int ProcessReconEvent(RF_Raid_t *, RF_ReconEvent_t *);
static int IssueNextReadRequest(RF_Raid_t *, RF_RowCol_t);
static int TryToRead(RF_Raid_t *, RF_RowCol_t);
static int ComputePSDiskOffsets(RF_Raid_t *, RF_StripeNum_t, RF_RowCol_t,
				RF_SectorNum_t *, RF_SectorNum_t *, RF_RowCol_t *,
				RF_SectorNum_t *);
static int IssueNextWriteRequest(RF_Raid_t *);
static int ReconReadDoneProc(void *, int);
static int ReconWriteDoneProc(void *, int);
static void CheckForNewMinHeadSep(RF_Raid_t *, RF_HeadSepLimit_t);
static int CheckHeadSeparation(RF_Raid_t *, RF_PerDiskReconCtrl_t *,
			       RF_RowCol_t, RF_HeadSepLimit_t,
			       RF_ReconUnitNum_t);
static int CheckForcedOrBlockedReconstruction(RF_Raid_t *,
					      RF_ReconParityStripeStatus_t *,
					      RF_PerDiskReconCtrl_t *,
					      RF_RowCol_t, RF_StripeNum_t,
					      RF_ReconUnitNum_t);
static void ForceReconReadDoneProc(void *, int);
static void rf_ShutdownReconstruction(void *);

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

/**************************************************************************
 *
 * 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(void *ignored)
{
	pool_destroy(&rf_pools.reconbuffer);
}

int
rf_ConfigureReconstruction(RF_ShutdownList_t **listp)
{

	rf_pool_init(&rf_pools.reconbuffer, sizeof(RF_ReconBuffer_t),
		     "rf_reconbuffer_pl", RF_MIN_FREE_RECONBUFFER, RF_MAX_FREE_RECONBUFFER);
	rf_ShutdownCreate(listp, rf_ShutdownReconstruction, NULL);

	return (0);
}

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

	RF_RaidReconDesc_t *reconDesc;

	RF_Malloc(reconDesc, sizeof(RF_RaidReconDesc_t),
		  (RF_RaidReconDesc_t *));
	reconDesc->raidPtr = raidPtr;
	reconDesc->col = col;
	reconDesc->spareDiskPtr = spareDiskPtr;
	reconDesc->numDisksDone = numDisksDone;
	reconDesc->scol = scol;
	reconDesc->next = NULL;

	return (reconDesc);
}

static void
FreeReconDesc(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_Free(reconDesc, sizeof(RF_RaidReconDesc_t));
}


/*****************************************************************************
 *
 * 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(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(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 RF_INCLUDE_PARITY_DECLUSTERING_DS > 0
	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 {
#endif
		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);
#if RF_INCLUDE_PARITY_DECLUSTERING_DS > 0
	}
#endif
	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);

	} else {
		/* Reconstruct failed. */

		RF_LOCK_MUTEX(raidPtr->mutex);
		/* Failed disk goes back to "failed" status */
		raidPtr->Disks[col].status = rf_ds_failed;

		/* Spare disk goes back to "spare" status. */
		spareDiskPtr->status = rf_ds_spare;
		RF_UNLOCK_MUTEX(raidPtr->mutex);

	}
	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(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;
	int retcode;
	int ac;

	lp = raidPtr->Layout.map;
	if (!lp->SubmitReconBuffer) {
		RF_ERRORMSG1("RECON: no way to reconstruct failed disk for arch %c\n",
			     lp->parityConfig);
		/* wakeup anyone who might be waiting to do a reconstruct */
		RF_SIGNAL_COND(raidPtr->waitForReconCond);
		return(EIO);
	}

	/*
	 * 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 effects. */
	/* RF_ASSERT(raidPtr->Disks[col].status == rf_ds_failed); */

#if RF_INCLUDE_PARITY_DECLUSTERING_DS > 0
	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);
		RF_SIGNAL_COND(raidPtr->waitForReconCond);
		return (EINVAL);
	}
#endif

	/* 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 = dk_lookup(raidPtr->Disks[col].devname, curlwp, &vp, UIO_SYSSPACE);

	if (retcode) {
		printf("raid%d: rebuilding: dk_lookup 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);
		RF_SIGNAL_COND(raidPtr->waitForReconCond);
		return(retcode);
	}

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

	if ((retcode = VOP_GETATTR(vp, &va, curlwp->l_cred)) != 0) {
		RF_LOCK_MUTEX(raidPtr->mutex);
		raidPtr->reconInProgress--;
		RF_UNLOCK_MUTEX(raidPtr->mutex);
		RF_SIGNAL_COND(raidPtr->waitForReconCond);
		return(retcode);
	}

	retcode = VOP_IOCTL(vp, DIOCGPART, &dpart, FREAD, curlwp->l_cred);
	if (retcode) {
		RF_LOCK_MUTEX(raidPtr->mutex);
		raidPtr->reconInProgress--;
		RF_UNLOCK_MUTEX(raidPtr->mutex);
		RF_SIGNAL_COND(raidPtr->waitForReconCond);
		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);

	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);

	} else {
		/* Reconstruct-in-place failed.  Disk goes back to
		   "failed" status, regardless of what it was before.  */
		RF_LOCK_MUTEX(raidPtr->mutex);
		raidPtr->Disks[col].status = rf_ds_failed;
		RF_UNLOCK_MUTEX(raidPtr->mutex);
	}

	rf_update_component_labels(raidPtr, RF_NORMAL_COMPONENT_UPDATE);

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

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


int
rf_ContinueReconstructFailedDisk(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;
	RF_StripeCount_t incPSID,lastPSID,num_writes,pending_writes,prev;
	RF_ReconUnitCount_t RUsPerPU;
	struct timeval etime, elpsd;
	unsigned long xor_s, xor_resid_us;
	int     i, ds;
	int status, done;
	int recon_error, write_error;

	raidPtr->accumXorTimeUs = 0;
#if RF_ACC_TRACE > 0
	/* create one trace record per physical disk */
	RF_Malloc(raidPtr->recon_tracerecs, raidPtr->numCol * sizeof(RF_AccTraceEntry_t), (RF_AccTraceEntry_t *));
#endif

	/* 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. */

	Dprintf("RECON: begin request suspend\n");
	rf_SuspendNewRequestsAndWait(raidPtr);
	Dprintf("RECON: end request suspend\n");

	/* 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->reconControl->numRUsTotal = mapPtr->totalRUs;
	raidPtr->reconControl->numRUsComplete =	0;
	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);

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


	mapPtr = raidPtr->reconControl->reconMap;

	incPSID = RF_RECONMAP_SIZE;
	lastPSID = raidPtr->Layout.numStripe / raidPtr->Layout.SUsPerPU;
	RUsPerPU = raidPtr->Layout.SUsPerPU / raidPtr->Layout.SUsPerRU;
	recon_error = 0;
	write_error = 0;
	pending_writes = incPSID;
	raidPtr->reconControl->lastPSID = incPSID;

	/* start the actual reconstruction */

	done = 0;
	while (!done) {

		num_writes = 0;

		/* 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++;
				}
			}
		}

		/* process reconstruction events until all disks report that
		 * they've completed all work */

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

			event = rf_GetNextReconEvent(reconDesc);
			status = ProcessReconEvent(raidPtr, event);

			/* the normal case is that a read completes, and all is well. */
			if (status == RF_RECON_DONE_READS) {
				reconDesc->numDisksDone++;
			} else if ((status == RF_RECON_READ_ERROR) ||
				   (status == RF_RECON_WRITE_ERROR)) {
				/* an error was encountered while reconstructing...
				   Pretend we've finished this disk.
				*/
				recon_error = 1;
				raidPtr->reconControl->error = 1;

				/* bump the numDisksDone count for reads,
				   but not for writes */
				if (status == RF_RECON_READ_ERROR)
					reconDesc->numDisksDone++;

				/* write errors are special -- when we are
				   done dealing with the reads that are
				   finished, we don't want to wait for any
				   writes */
				if (status == RF_RECON_WRITE_ERROR)
					write_error = 1;

			} else if (status == RF_RECON_READ_STOPPED) {
				/* count this component as being "done" */
				reconDesc->numDisksDone++;
			} else if (status == RF_RECON_WRITE_DONE) {
				num_writes++;
			}

			if (recon_error) {
				/* make sure any stragglers are woken up so that
				   their theads will complete, and we can get out
				   of here with all IO processed */

				rf_WakeupHeadSepCBWaiters(raidPtr);
			}

			raidPtr->reconControl->numRUsTotal =
				mapPtr->totalRUs;
			raidPtr->reconControl->numRUsComplete =
				mapPtr->totalRUs -
				rf_UnitsLeftToReconstruct(mapPtr);

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

		/* reads done, wakup any waiters, and then wait for writes */

		rf_WakeupHeadSepCBWaiters(raidPtr);

		while (!recon_error && (num_writes < pending_writes)) {
			event = rf_GetNextReconEvent(reconDesc);
			status = ProcessReconEvent(raidPtr, event);

			if (status == RF_RECON_WRITE_ERROR) {
				recon_error = 1;
				raidPtr->reconControl->error = 1;
				/* an error was encountered at the very end... bail */
			} else if (status == RF_RECON_WRITE_DONE) {
				num_writes++;
			}
		}
		if (recon_error ||
		    (raidPtr->reconControl->lastPSID == lastPSID)) {
			done = 1;
			break;
		}

		prev = raidPtr->reconControl->lastPSID;
		raidPtr->reconControl->lastPSID += incPSID;

		if (raidPtr->reconControl->lastPSID > lastPSID) {
			pending_writes = lastPSID - prev;
			raidPtr->reconControl->lastPSID = lastPSID;
		}

		/* back down curPSID to get ready for the next round... */
		for (i = 0; i < raidPtr->numCol; i++) {
			if (i != col) {
				raidPtr->reconControl->perDiskInfo[i].curPSID--;
				raidPtr->reconControl->perDiskInfo[i].ru_count = RUsPerPU - 1;
			}
		}
	}

	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 (!recon_error && rf_UnitsLeftToReconstruct(raidPtr->reconControl->reconMap) > 0) {

		event = rf_GetNextReconEvent(reconDesc);
		status = ProcessReconEvent(raidPtr, event);

		if (status == RF_RECON_WRITE_ERROR) {
			recon_error = 1;
			raidPtr->reconControl->error = 1;
			/* an error was encountered at the very end... bail */
		} else {
#if RF_DEBUG_RECON
			raidPtr->reconControl->percentComplete = 100 - (rf_UnitsLeftToReconstruct(mapPtr) * 100 / mapPtr->totalRUs);
			if (rf_prReconSched) {
				rf_PrintReconSchedule(raidPtr->reconControl->reconMap, &(raidPtr->reconControl->starttime));
			}
#endif
		}
	}

	if (recon_error) {
		/* we've encountered an error in reconstructing. */
		printf("raid%d: reconstruction failed.\n", raidPtr->raidid);

		/* we start by blocking IO to the RAID set. */
		rf_SuspendNewRequestsAndWait(raidPtr);

		RF_LOCK_MUTEX(raidPtr->mutex);
		/* mark set as being degraded, rather than
		   rf_rs_reconstructing as we were before the problem.
		   After this is done we can update status of the
		   component disks without worrying about someone
		   trying to read from a failed component.
		*/
		raidPtr->status = rf_rs_degraded;
		RF_UNLOCK_MUTEX(raidPtr->mutex);

		/* resume IO */
		rf_ResumeNewRequests(raidPtr);

		/* At this point there are two cases:
		   1) If we've experienced a read error, then we've
		   already waited for all the reads we're going to get,
		   and we just need to wait for the writes.

		   2) If we've experienced a write error, we've also
		   already waited for all the reads to complete,
		   but there is little point in waiting for the writes --
		   when they do complete, they will just be ignored.

		   So we just wait for writes to complete if we didn't have a
		   write error.
		*/

		if (!write_error) {
			/* wait for writes to complete */
			while (raidPtr->reconControl->pending_writes > 0) {

				event = rf_GetNextReconEvent(reconDesc);
				status = ProcessReconEvent(raidPtr, event);

				if (status == RF_RECON_WRITE_ERROR) {
					raidPtr->reconControl->error = 1;
					/* an error was encountered at the very end... bail.
					   This will be very bad news for the user, since
					   at this point there will have been a read error
					   on one component, and a write error on another!
					*/
					break;
				}
			}
		}


		/* cleanup */

		/* drain the event queue - after waiting for the writes above,
		   there shouldn't be much (if anything!) left in the queue. */

		rf_DrainReconEventQueue(reconDesc);

		/* XXX  As much as we'd like to free the recon control structure
		   and the reconDesc, we have no way of knowing if/when those will
		   be touched by IO that has yet to occur.  It is rather poor to be
		   basically causing a 'memory leak' here, but there doesn't seem to be
		   a cleaner alternative at this time.  Perhaps when the reconstruct code
		   gets a makeover this problem will go away.
		*/
#if 0
		rf_FreeReconControl(raidPtr);
#endif

#if RF_ACC_TRACE > 0
		RF_Free(raidPtr->recon_tracerecs, raidPtr->numCol * sizeof(RF_AccTraceEntry_t));
#endif
		/* XXX see comment above */
#if 0
		FreeReconDesc(reconDesc);
#endif

		return (1);
	}

	/* 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() */

	rf_SuspendNewRequestsAndWait(raidPtr);

	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);

	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);
#if RF_ACC_TRACE > 0
	RF_Free(raidPtr->recon_tracerecs, raidPtr->numCol * sizeof(RF_AccTraceEntry_t));
#endif
	FreeReconDesc(reconDesc);

	return (0);

}
/*****************************************************************************
 * do the right thing upon each reconstruction event.
 *****************************************************************************/
static int
ProcessReconEvent(RF_Raid_t *raidPtr, RF_ReconEvent_t *event)
{
	int     retcode = 0, submitblocked;
	RF_ReconBuffer_t *rbuf;
	RF_SectorCount_t sectorsPerRU;

	retcode = RF_RECON_READ_STOPPED;

	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);
		if (!raidPtr->reconControl->error) {
			submitblocked = rf_SubmitReconBuffer(rbuf, 0, 0);
			Dprintf1("RECON: submitblocked=%d\n", submitblocked);
			if (!submitblocked)
				retcode = IssueNextReadRequest(raidPtr, event->col);
			else
				retcode = 0;
		}
		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);

		RF_LOCK_MUTEX(raidPtr->reconControl->rb_mutex);
		raidPtr->reconControl->pending_writes--;
		RF_UNLOCK_MUTEX(raidPtr->reconControl->rb_mutex);

		if (rbuf->type == RF_RBUF_TYPE_FLOATING) {
			RF_LOCK_MUTEX(raidPtr->reconControl->rb_mutex);
			while(raidPtr->reconControl->rb_lock) {
				ltsleep(&raidPtr->reconControl->rb_lock, PRIBIO, "reconctrlpre1", 0,
					&raidPtr->reconControl->rb_mutex);
			}
			raidPtr->reconControl->rb_lock = 1;
			RF_UNLOCK_MUTEX(raidPtr->reconControl->rb_mutex);

			raidPtr->numFullReconBuffers--;
			rf_ReleaseFloatingReconBuffer(raidPtr, rbuf);

			RF_LOCK_MUTEX(raidPtr->reconControl->rb_mutex);
			raidPtr->reconControl->rb_lock = 0;
			wakeup(&raidPtr->reconControl->rb_lock);
			RF_UNLOCK_MUTEX(raidPtr->reconControl->rb_mutex);
		} else
			if (rbuf->type == RF_RBUF_TYPE_FORCED)
				rf_FreeReconBuffer(rbuf);
			else
				RF_ASSERT(0);
		retcode = RF_RECON_WRITE_DONE;
		break;

	case RF_REVENT_BUFCLEAR:	/* A buffer-stall condition has been
					 * cleared */
		Dprintf1("RECON: BUFCLEAR EVENT: col %d\n", event->col);
		if (!raidPtr->reconControl->error) {
			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);
		if (!raidPtr->reconControl->error) {
			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);
		if (!raidPtr->reconControl->error) {
			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);
		if (!raidPtr->reconControl->error) {
			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);
		if (!raidPtr->reconControl->error) {
			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);
		if (!raidPtr->reconControl->error) {
			submitblocked = rf_SubmitReconBuffer(rbuf, 1, 0);
			RF_ASSERT(!submitblocked);
			retcode = 0;
		}
		break;

		/* A read I/O failed to complete */
	case RF_REVENT_READ_FAILED:
		retcode = RF_RECON_READ_ERROR;
		break;

		/* A write I/O failed to complete */
	case RF_REVENT_WRITE_FAILED:
		retcode = RF_RECON_WRITE_ERROR;

		rbuf = (RF_ReconBuffer_t *) event->arg;

		/* cleanup the disk queue data */
		rf_FreeDiskQueueData((RF_DiskQueueData_t *) rbuf->arg);

		/* At this point we're erroring out, badly, and floatingRbufs
		   may not even be valid.  Rather than putting this back onto
		   the floatingRbufs list, just arrange for its immediate
		   destruction.
		*/
		rf_FreeReconBuffer(rbuf);
		break;

		/* a forced read I/O failed to complete */
	case RF_REVENT_FORCEDREAD_FAILED:
		retcode = RF_RECON_READ_ERROR;
		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.
 *
 *****************************************************************************/
static int
IssueNextReadRequest(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 (RF_RECON_DONE_READS);	/* 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;
#if RF_ACC_TRACE > 0
	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);
#endif
	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(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;
	RF_ReconParityStripeStatus_t *pssPtr, *newpssPtr;

	/* 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);

	/* allocate a new PSS in case we need it */
	newpssPtr = rf_AllocPSStatus(raidPtr);

	RF_LOCK_PSS_MUTEX(raidPtr, psid);
	pssPtr = rf_LookupRUStatus(raidPtr, raidPtr->reconControl->pssTable, psid, which_ru, RF_PSS_CREATE, newpssPtr);

	if (pssPtr != newpssPtr) {
		rf_FreePSStatus(raidPtr, newpssPtr);
	}

	/* 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 (pssPtr == newpssPtr)
			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);
#if RF_ACC_TRACE > 0
	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);
#endif
	/* 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,
#if RF_ACC_TRACE > 0
				     &raidPtr->recon_tracerecs[col],
#else
				     NULL,
#endif
				     (void *) raidPtr, 0, NULL, PR_WAITOK);

	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
 *
 * raidPtr          - raid descriptor
 * psid             - parity stripe identifier
 * col              - column of disk to find the offsets for
 * spCol            - out: col of spare unit for failed unit
 * spOffset         - out: offset into disk containing spare unit
 *
 */


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)
{
	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 RF_INCLUDE_PARITY_DECLUSTERING_DS > 0
	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 {
#endif
		*spCol = raidPtr->reconControl->spareCol;
		*spOffset = *outFailedDiskSectorOffset;
#if RF_INCLUDE_PARITY_DECLUSTERING_DS > 0
	}
#endif
	return (0);

skipit:
	Dprintf2("RECON: Skipping psid %ld: nothing needed from 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(RF_Raid_t *raidPtr)
{
	RF_RaidLayout_t *layoutPtr = &raidPtr->Layout;
	RF_SectorCount_t sectorsPerRU = layoutPtr->sectorsPerStripeUnit * layoutPtr->SUsPerRU;
#if RF_ACC_TRACE > 0
	RF_RowCol_t fcol = raidPtr->reconControl->fcol;
#endif
	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,
#if RF_ACC_TRACE > 0
	    &raidPtr->recon_tracerecs[fcol],
#else
				     NULL,
#endif
	    (void *) raidPtr, 0, NULL, PR_WAITOK);

	rbuf->arg = (void *) req;
	RF_LOCK_MUTEX(raidPtr->reconControl->rb_mutex);
	raidPtr->reconControl->pending_writes++;
	RF_UNLOCK_MUTEX(raidPtr->reconControl->rb_mutex);
	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(void *arg, int status)
{
	RF_PerDiskReconCtrl_t *ctrl = (RF_PerDiskReconCtrl_t *) arg;
	RF_Raid_t *raidPtr;

	/* Detect that reconCtrl is no longer valid, and if that
	   is the case, bail without calling rf_CauseReconEvent().
	   There won't be anyone listening for this event anyway */

	if (ctrl->reconCtrl == NULL)
		return(0);

	raidPtr = ctrl->reconCtrl->reconDesc->raidPtr;

	if (status) {
		printf("raid%d: Recon read failed: %d\n", raidPtr->raidid, status);
		rf_CauseReconEvent(raidPtr, ctrl->col, NULL, RF_REVENT_READ_FAILED);
		return(0);
	}
#if RF_ACC_TRACE > 0
	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);
#endif
	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(void *arg, int status)
{
	RF_ReconBuffer_t *rbuf = (RF_ReconBuffer_t *) arg;

	/* Detect that reconControl is no longer valid, and if that
	   is the case, bail without calling rf_CauseReconEvent().
	   There won't be anyone listening for this event anyway */

	if (rbuf->raidPtr->reconControl == NULL)
		return(0);

	Dprintf2("Reconstruction completed on psid %ld ru %d\n", rbuf->parityStripeID, rbuf->which_ru);
	if (status) {
		printf("raid%d: Recon write failed!\n", rbuf->raidPtr->raidid);
		rf_CauseReconEvent(rbuf->raidPtr, rbuf->col, arg, RF_REVENT_WRITE_FAILED);
		return(0);
	}
	rf_CauseReconEvent(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(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);
	while(reconCtrlPtr->rb_lock) {
		ltsleep(&reconCtrlPtr->rb_lock, PRIBIO, "reconctlcnmhs", 0, &reconCtrlPtr->rb_mutex);
	}
	reconCtrlPtr->rb_lock = 1;
	RF_UNLOCK_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_LOCK_MUTEX(reconCtrlPtr->rb_mutex);
	reconCtrlPtr->rb_lock = 0;
	wakeup(&reconCtrlPtr->rb_lock);
	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);
	while(reconCtrlPtr->rb_lock) {
		ltsleep(&reconCtrlPtr->rb_lock, PRIBIO, "reconctlchs", 0, &reconCtrlPtr->rb_mutex);
	}
	reconCtrlPtr->rb_lock = 1;
	RF_UNLOCK_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_LOCK_MUTEX(reconCtrlPtr->rb_mutex);
	reconCtrlPtr->rb_lock = 0;
	wakeup(&reconCtrlPtr->rb_lock);
	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(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, *newpssPtr;	/* 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     nPromoted;

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

	/* allocate a new PSS in case we need it */
        newpssPtr = rf_AllocPSStatus(raidPtr);

	RF_LOCK_PSS_MUTEX(raidPtr, psid);

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

        if (pssPtr != newpssPtr) {
                rf_FreePSStatus(raidPtr, newpssPtr);
        }

	/* 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, (void *) raidPtr, 0, NULL, PR_WAITOK);

					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))
			if (rf_reconDebug)
				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(void *arg, int status)
{
	RF_ReconBuffer_t *rbuf = arg;

	/* Detect that reconControl is no longer valid, and if that
	   is the case, bail without calling rf_CauseReconEvent().
	   There won't be anyone listening for this event anyway */

	if (rbuf->raidPtr->reconControl == NULL)
		return;

	if (status) {
		printf("raid%d: Forced recon read failed!\n", rbuf->raidPtr->raidid);
		rf_CauseReconEvent(rbuf->raidPtr, rbuf->col, (void *) rbuf, RF_REVENT_FORCEDREAD_FAILED);
		return;
	}
	rf_CauseReconEvent(rbuf->raidPtr, rbuf->col, (void *) rbuf, RF_REVENT_FORCEDREADDONE);
}
/* releases a block on the reconstruction of the indicated stripe */
int
rf_UnblockRecon(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;
	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, NULL);

	/* 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);
}

void
rf_WakeupHeadSepCBWaiters(RF_Raid_t *raidPtr)
{
	RF_CallbackDesc_t *p;

	RF_LOCK_MUTEX(raidPtr->reconControl->rb_mutex);
	while(raidPtr->reconControl->rb_lock) {
		ltsleep(&raidPtr->reconControl->rb_lock, PRIBIO,
			"rf_wakeuphscbw", 0, &raidPtr->reconControl->rb_mutex);
	}

	raidPtr->reconControl->rb_lock = 1;
	RF_UNLOCK_MUTEX(raidPtr->reconControl->rb_mutex);

	while (raidPtr->reconControl->headSepCBList) {
		p = raidPtr->reconControl->headSepCBList;
		raidPtr->reconControl->headSepCBList = p->next;
		p->next = NULL;
		rf_CauseReconEvent(raidPtr, p->col, NULL, RF_REVENT_HEADSEPCLEAR);
		rf_FreeCallbackDesc(p);
	}
	RF_LOCK_MUTEX(raidPtr->reconControl->rb_mutex);
	raidPtr->reconControl->rb_lock = 0;
	wakeup(&raidPtr->reconControl->rb_lock);
	RF_UNLOCK_MUTEX(raidPtr->reconControl->rb_mutex);

}