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/export.h>
  22 #include <linux/raid/pq.h>
  23
  24 /* Recover two failed data blocks. */
  25 void raid6_2data_recov(int disks, size_t bytes, int faila, int failb,
  26                        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 EXPORT_SYMBOL_GPL(raid6_2data_recov);
  68
  69 /* Recover failure of one data block plus the P block */
  70 void raid6_datap_recov(int disks, size_t bytes, int faila, 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 EXPORT_SYMBOL_GPL(raid6_datap_recov);
 100
 101 #ifndef __KERNEL__
 102 /* Testing only */
 103
 104 /* Recover two failed blocks. */
 105 void 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