linux/lib/raid6/recov.c
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   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 *   Boston 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 * raid6/recov.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 <linux/export.h>
  22#include <linux/raid/pq.h>
  23
  24/* Recover two failed data blocks. */
  25static void raid6_2data_recov_intx1(int disks, size_t bytes, int faila,
  26                int failb, void **ptrs)
  27{
  28        u8 *p, *q, *dp, *dq;
  29        u8 px, qx, db;
  30        const u8 *pbmul;        /* P multiplier table for B data */
  31        const u8 *qmul;         /* Q multiplier table (for both) */
  32
  33        p = (u8 *)ptrs[disks-2];
  34        q = (u8 *)ptrs[disks-1];
  35
  36        /* Compute syndrome with zero for the missing data pages
  37           Use the dead data pages as temporary storage for
  38           delta p and delta q */
  39        dp = (u8 *)ptrs[faila];
  40        ptrs[faila] = (void *)raid6_empty_zero_page;
  41        ptrs[disks-2] = dp;
  42        dq = (u8 *)ptrs[failb];
  43        ptrs[failb] = (void *)raid6_empty_zero_page;
  44        ptrs[disks-1] = dq;
  45
  46        raid6_call.gen_syndrome(disks, bytes, ptrs);
  47
  48        /* Restore pointer table */
  49        ptrs[faila]   = dp;
  50        ptrs[failb]   = dq;
  51        ptrs[disks-2] = p;
  52        ptrs[disks-1] = q;
  53
  54        /* Now, pick the proper data tables */
  55        pbmul = raid6_gfmul[raid6_gfexi[failb-faila]];
  56        qmul  = raid6_gfmul[raid6_gfinv[raid6_gfexp[faila]^raid6_gfexp[failb]]];
  57
  58        /* Now do it... */
  59        while ( bytes-- ) {
  60                px    = *p ^ *dp;
  61                qx    = qmul[*q ^ *dq];
  62                *dq++ = db = pbmul[px] ^ qx; /* Reconstructed B */
  63                *dp++ = db ^ px; /* Reconstructed A */
  64                p++; q++;
  65        }
  66}
  67
  68/* Recover failure of one data block plus the P block */
  69static void raid6_datap_recov_intx1(int disks, size_t bytes, int faila,
  70                void **ptrs)
  71{
  72        u8 *p, *q, *dq;
  73        const u8 *qmul;         /* Q multiplier table */
  74
  75        p = (u8 *)ptrs[disks-2];
  76        q = (u8 *)ptrs[disks-1];
  77
  78        /* Compute syndrome with zero for the missing data page
  79           Use the dead data page as temporary storage for delta q */
  80        dq = (u8 *)ptrs[faila];
  81        ptrs[faila] = (void *)raid6_empty_zero_page;
  82        ptrs[disks-1] = dq;
  83
  84        raid6_call.gen_syndrome(disks, bytes, ptrs);
  85
  86        /* Restore pointer table */
  87        ptrs[faila]   = dq;
  88        ptrs[disks-1] = q;
  89
  90        /* Now, pick the proper data tables */
  91        qmul  = raid6_gfmul[raid6_gfinv[raid6_gfexp[faila]]];
  92
  93        /* Now do it... */
  94        while ( bytes-- ) {
  95                *p++ ^= *dq = qmul[*q ^ *dq];
  96                q++; dq++;
  97        }
  98}
  99
 100
 101const struct raid6_recov_calls raid6_recov_intx1 = {
 102        .data2 = raid6_2data_recov_intx1,
 103        .datap = raid6_datap_recov_intx1,
 104        .valid = NULL,
 105        .name = "intx1",
 106        .priority = 0,
 107};
 108
 109#ifndef __KERNEL__
 110/* Testing only */
 111
 112/* Recover two failed blocks. */
 113void raid6_dual_recov(int disks, size_t bytes, int faila, int failb, void **ptrs)
 114{
 115        if ( faila > failb ) {
 116                int tmp = faila;
 117                faila = failb;
 118                failb = tmp;
 119        }
 120
 121        if ( failb == disks-1 ) {
 122                if ( faila == disks-2 ) {
 123                        /* P+Q failure.  Just rebuild the syndrome. */
 124                        raid6_call.gen_syndrome(disks, bytes, ptrs);
 125                } else {
 126                        /* data+Q failure.  Reconstruct data from P,
 127                           then rebuild syndrome. */
 128                        /* NOT IMPLEMENTED - equivalent to RAID-5 */
 129                }
 130        } else {
 131                if ( failb == disks-2 ) {
 132                        /* data+P failure. */
 133                        raid6_datap_recov(disks, bytes, faila, ptrs);
 134                } else {
 135                        /* data+data failure. */
 136                        raid6_2data_recov(disks, bytes, faila, failb, ptrs);
 137                }
 138        }
 139}
 140
 141#endif
 142
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