LXR linux/drivers/md/raid6recov.c

   1/* -*- linux-c -*- ------------------------------------------------------- *
   2 *
   3 *   Copyright 2002 H. Peter Anvin - All Rights Reserved
   4 *
   5 *   This program is free software; you can redistribute it and/or modify
   6 *   it under the terms of the GNU General Public License as published by
   7 *   the Free Software Foundation, Inc., 53 Temple Place Ste 330,
   8 *   Bostom MA 02111-1307, USA; either version 2 of the License, or
   9 *   (at your option) any later version; incorporated herein by reference.
  10 *
  11 * ----------------------------------------------------------------------- */
  12
  13/*
  14 * raid6recov.c
  15 *
  16 * RAID-6 data recovery in dual failure mode.  In single failure mode,
  17 * use the RAID-5 algorithm (or, in the case of Q failure, just reconstruct
  18 * the syndrome.)
  19 */
  20
  21#include "raid6.h"
  22
  23/* Recover two failed data blocks. */
  24void raid6_2data_recov(int disks, size_t bytes, int faila, int failb,
  25                       void **ptrs)
  26{
  27        u8 *p, *q, *dp, *dq;
  28        u8 px, qx, db;
  29        const u8 *pbmul;        /* P multiplier table for B data */
  30        const u8 *qmul;         /* Q multiplier table (for both) */
  31
  32        p = (u8 *)ptrs[disks-2];
  33        q = (u8 *)ptrs[disks-1];
  34
  35        /* Compute syndrome with zero for the missing data pages
  36           Use the dead data pages as temporary storage for
  37           delta p and delta q */
  38        dp = (u8 *)ptrs[faila];
  39        ptrs[faila] = (void *)raid6_empty_zero_page;
  40        ptrs[disks-2] = dp;
  41        dq = (u8 *)ptrs[failb];
  42        ptrs[failb] = (void *)raid6_empty_zero_page;
  43        ptrs[disks-1] = dq;
  44
  45        raid6_call.gen_syndrome(disks, bytes, ptrs);
  46
  47        /* Restore pointer table */
  48        ptrs[faila]   = dp;
  49        ptrs[failb]   = dq;
  50        ptrs[disks-2] = p;
  51        ptrs[disks-1] = q;
  52
  53        /* Now, pick the proper data tables */
  54        pbmul = raid6_gfmul[raid6_gfexi[failb-faila]];
  55        qmul  = raid6_gfmul[raid6_gfinv[raid6_gfexp[faila]^raid6_gfexp[failb]]];
  56
  57        /* Now do it... */
  58        while ( bytes-- ) {
  59                px    = *p ^ *dp;
  60                qx    = qmul[*q ^ *dq];
  61                *dq++ = db = pbmul[px] ^ qx; /* Reconstructed B */
  62                *dp++ = db ^ px; /* Reconstructed A */
  63                p++; q++;
  64        }
  65}
  66
  67
  68
  69
  70/* Recover failure of one data block plus the P block */
  71void raid6_datap_recov(int disks, size_t bytes, int faila, void **ptrs)
  72{
  73        u8 *p, *q, *dq;
  74        const u8 *qmul;         /* Q multiplier table */
  75
  76        p = (u8 *)ptrs[disks-2];
  77        q = (u8 *)ptrs[disks-1];
  78
  79        /* Compute syndrome with zero for the missing data page
  80           Use the dead data page as temporary storage for delta q */
  81        dq = (u8 *)ptrs[faila];
  82        ptrs[faila] = (void *)raid6_empty_zero_page;
  83        ptrs[disks-1] = dq;
  84
  85        raid6_call.gen_syndrome(disks, bytes, ptrs);
  86
  87        /* Restore pointer table */
  88        ptrs[faila]   = dq;
  89        ptrs[disks-1] = q;
  90
  91        /* Now, pick the proper data tables */
  92        qmul  = raid6_gfmul[raid6_gfinv[raid6_gfexp[faila]]];
  93
  94        /* Now do it... */
  95        while ( bytes-- ) {
  96                *p++ ^= *dq = qmul[*q ^ *dq];
  97                q++; dq++;
  98        }
  99}
 100
 101
 102#ifndef __KERNEL__              /* Testing only */
 103
 104/* Recover two failed blocks. */
 105void raid6_dual_recov(int disks, size_t bytes, int faila, int failb, void **ptrs)
 106{
 107        if ( faila > failb ) {
 108                int tmp = faila;
 109                faila = failb;
 110                failb = tmp;
 111        }
 112
 113        if ( failb == disks-1 ) {
 114                if ( faila == disks-2 ) {
 115                        /* P+Q failure.  Just rebuild the syndrome. */
 116                        raid6_call.gen_syndrome(disks, bytes, ptrs);
 117                } else {
 118                        /* data+Q failure.  Reconstruct data from P,
 119                           then rebuild syndrome. */
 120                        /* NOT IMPLEMENTED - equivalent to RAID-5 */
 121                }
 122        } else {
 123                if ( failb == disks-2 ) {
 124                        /* data+P failure. */
 125                        raid6_datap_recov(disks, bytes, faila, ptrs);
 126                } else {
 127                        /* data+data failure. */
 128                        raid6_2data_recov(disks, bytes, faila, failb, ptrs);
 129                }
 130        }
 131}
 132
 133#endif
 134