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raid6recov.c

/* -*- linux-c -*- ------------------------------------------------------- *
 *
 *   Copyright 2002 H. Peter Anvin - All Rights Reserved
 *
 *   This program is free software; you can redistribute it and/or modify
 *   it under the terms of the GNU General Public License as published by
 *   the Free Software Foundation, Inc., 53 Temple Place Ste 330,
 *   Bostom MA 02111-1307, USA; either version 2 of the License, or
 *   (at your option) any later version; incorporated herein by reference.
 *
 * ----------------------------------------------------------------------- */

/*
 * raid6recov.c
 *
 * RAID-6 data recovery in dual failure mode.  In single failure mode,
 * use the RAID-5 algorithm (or, in the case of Q failure, just reconstruct
 * the syndrome.)
 */

#include "raid6.h"

/* Recover two failed data blocks. */
void raid6_2data_recov(int disks, size_t bytes, int faila, int failb,
                   void **ptrs)
{
      u8 *p, *q, *dp, *dq;
      u8 px, qx, db;
      const u8 *pbmul;  /* P multiplier table for B data */
      const u8 *qmul;         /* Q multiplier table (for both) */

      p = (u8 *)ptrs[disks-2];
      q = (u8 *)ptrs[disks-1];

      /* Compute syndrome with zero for the missing data pages
         Use the dead data pages as temporary storage for
         delta p and delta q */
      dp = (u8 *)ptrs[faila];
      ptrs[faila] = (void *)raid6_empty_zero_page;
      ptrs[disks-2] = dp;
      dq = (u8 *)ptrs[failb];
      ptrs[failb] = (void *)raid6_empty_zero_page;
      ptrs[disks-1] = dq;

      raid6_call.gen_syndrome(disks, bytes, ptrs);

      /* Restore pointer table */
      ptrs[faila]   = dp;
      ptrs[failb]   = dq;
      ptrs[disks-2] = p;
      ptrs[disks-1] = q;

      /* Now, pick the proper data tables */
      pbmul = raid6_gfmul[raid6_gfexi[failb-faila]];
      qmul  = raid6_gfmul[raid6_gfinv[raid6_gfexp[faila]^raid6_gfexp[failb]]];

      /* Now do it... */
      while ( bytes-- ) {
            px    = *p ^ *dp;
            qx    = qmul[*q ^ *dq];
            *dq++ = db = pbmul[px] ^ qx; /* Reconstructed B */
            *dp++ = db ^ px; /* Reconstructed A */
            p++; q++;
      }
}




/* Recover failure of one data block plus the P block */
void raid6_datap_recov(int disks, size_t bytes, int faila, void **ptrs)
{
      u8 *p, *q, *dq;
      const u8 *qmul;         /* Q multiplier table */

      p = (u8 *)ptrs[disks-2];
      q = (u8 *)ptrs[disks-1];

      /* Compute syndrome with zero for the missing data page
         Use the dead data page as temporary storage for delta q */
      dq = (u8 *)ptrs[faila];
      ptrs[faila] = (void *)raid6_empty_zero_page;
      ptrs[disks-1] = dq;

      raid6_call.gen_syndrome(disks, bytes, ptrs);

      /* Restore pointer table */
      ptrs[faila]   = dq;
      ptrs[disks-1] = q;

      /* Now, pick the proper data tables */
      qmul  = raid6_gfmul[raid6_gfinv[raid6_gfexp[faila]]];

      /* Now do it... */
      while ( bytes-- ) {
            *p++ ^= *dq = qmul[*q ^ *dq];
            q++; dq++;
      }
}


#ifndef __KERNEL__            /* Testing only */

/* Recover two failed blocks. */
void raid6_dual_recov(int disks, size_t bytes, int faila, int failb, void **ptrs)
{
      if ( faila > failb ) {
            int tmp = faila;
            faila = failb;
            failb = tmp;
      }

      if ( failb == disks-1 ) {
            if ( faila == disks-2 ) {
                  /* P+Q failure.  Just rebuild the syndrome. */
                  raid6_call.gen_syndrome(disks, bytes, ptrs);
            } else {
                  /* data+Q failure.  Reconstruct data from P,
                     then rebuild syndrome. */
                  /* NOT IMPLEMENTED - equivalent to RAID-5 */
            }
      } else {
            if ( failb == disks-2 ) {
                  /* data+P failure. */
                  raid6_datap_recov(disks, bytes, faila, ptrs);
            } else {
                  /* data+data failure. */
                  raid6_2data_recov(disks, bytes, faila, failb, ptrs);
            }
      }
}

#endif

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