lib/raid6/recov.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  *   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/raid/pq.h>
  22
  23 /* Recover two failed data blocks. */
  24 void 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 EXPORT_SYMBOL_GPL(raid6_2data_recov);
  67
  68 /* Recover failure of one data block plus the P block */
  69 void raid6_datap_recov(int disks, size_t bytes, int faila, void **ptrs)
  70 {
  71         u8 *p, *q, *dq;
  72         const u8 *qmul;         /* Q multiplier table */
  73
  74         p = (u8 *)ptrs[disks-2];
  75         q = (u8 *)ptrs[disks-1];
  76
  77         /* Compute syndrome with zero for the missing data page
  78            Use the dead data page as temporary storage for delta q */
  79         dq = (u8 *)ptrs[faila];
  80         ptrs[faila] = (void *)raid6_empty_zero_page;
  81         ptrs[disks-1] = dq;
  82
  83         raid6_call.gen_syndrome(disks, bytes, ptrs);
  84
  85         /* Restore pointer table */
  86         ptrs[faila]   = dq;
  87         ptrs[disks-1] = q;
  88
  89         /* Now, pick the proper data tables */
  90         qmul  = raid6_gfmul[raid6_gfinv[raid6_gfexp[faila]]];
  91
  92         /* Now do it... */
  93         while ( bytes-- ) {
  94                 *p++ ^= *dq = qmul[*q ^ *dq];
  95                 q++; dq++;
  96         }
  97 }
  98 EXPORT_SYMBOL_GPL(raid6_datap_recov);
  99
 100 #ifndef __KERNEL__
 101 /* Testing only */
 102
 103 /* Recover two failed blocks. */
 104 void raid6_dual_recov(int disks, size_t bytes, int faila, int failb, void **ptrs)
 105 {
 106         if ( faila > failb ) {
 107                 int tmp = faila;
 108                 faila = failb;
 109                 failb = tmp;
 110         }
 111
 112         if ( failb == disks-1 ) {
 113                 if ( faila == disks-2 ) {
 114                         /* P+Q failure.  Just rebuild the syndrome. */
 115                         raid6_call.gen_syndrome(disks, bytes, ptrs);
 116                 } else {
 117                         /* data+Q failure.  Reconstruct data from P,
 118                            then rebuild syndrome. */
 119                         /* NOT IMPLEMENTED - equivalent to RAID-5 */
 120                 }
 121         } else {
 122                 if ( failb == disks-2 ) {
 123                         /* data+P failure. */
 124                         raid6_datap_recov(disks, bytes, faila, ptrs);
 125                 } else {
 126                         /* data+data failure. */
 127                         raid6_2data_recov(disks, bytes, faila, failb, ptrs);
 128                 }
 129         }
 130 }
 131
 132 #endif