lib/raid6/recov.c

   1 // SPDX-License-Identifier: GPL-2.0-or-later
   2 /* -*- linux-c -*- ------------------------------------------------------- *
   3  *
   4  *   Copyright 2002 H. Peter Anvin - All Rights Reserved
   5  *
   6  * ----------------------------------------------------------------------- */
   7
   8 /*
   9  * raid6/recov.c
  10  *
  11  * RAID-6 data recovery in dual failure mode.  In single failure mode,
  12  * use the RAID-5 algorithm (or, in the case of Q failure, just reconstruct
  13  * the syndrome.)
  14  */
  15
  16 #include <linux/raid/pq.h>
  17
  18 /* Recover two failed data blocks. */
  19 static void raid6_2data_recov_intx1(int disks, size_t bytes, int faila,
  20                 int failb, void **ptrs)
  21 {
  22         u8 *p, *q, *dp, *dq;
  23         u8 px, qx, db;
  24         const u8 *pbmul;        /* P multiplier table for B data */
  25         const u8 *qmul;         /* Q multiplier table (for both) */
  26
  27         p = (u8 *)ptrs[disks-2];
  28         q = (u8 *)ptrs[disks-1];
  29
  30         /* Compute syndrome with zero for the missing data pages
  31            Use the dead data pages as temporary storage for
  32            delta p and delta q */
  33         dp = (u8 *)ptrs[faila];
  34         ptrs[faila] = (void *)raid6_empty_zero_page;
  35         ptrs[disks-2] = dp;
  36         dq = (u8 *)ptrs[failb];
  37         ptrs[failb] = (void *)raid6_empty_zero_page;
  38         ptrs[disks-1] = dq;
  39
  40         raid6_call.gen_syndrome(disks, bytes, ptrs);
  41
  42         /* Restore pointer table */
  43         ptrs[faila]   = dp;
  44         ptrs[failb]   = dq;
  45         ptrs[disks-2] = p;
  46         ptrs[disks-1] = q;
  47
  48         /* Now, pick the proper data tables */
  49         pbmul = raid6_gfmul[raid6_gfexi[failb-faila]];
  50         qmul  = raid6_gfmul[raid6_gfinv[raid6_gfexp[faila]^raid6_gfexp[failb]]];
  51
  52         /* Now do it... */
  53         while ( bytes-- ) {
  54                 px    = *p ^ *dp;
  55                 qx    = qmul[*q ^ *dq];
  56                 *dq++ = db = pbmul[px] ^ qx; /* Reconstructed B */
  57                 *dp++ = db ^ px; /* Reconstructed A */
  58                 p++; q++;
  59         }
  60 }
  61
  62 /* Recover failure of one data block plus the P block */
  63 static void raid6_datap_recov_intx1(int disks, size_t bytes, int faila,
  64                 void **ptrs)
  65 {
  66         u8 *p, *q, *dq;
  67         const u8 *qmul;         /* Q multiplier table */
  68
  69         p = (u8 *)ptrs[disks-2];
  70         q = (u8 *)ptrs[disks-1];
  71
  72         /* Compute syndrome with zero for the missing data page
  73            Use the dead data page as temporary storage for delta q */
  74         dq = (u8 *)ptrs[faila];
  75         ptrs[faila] = (void *)raid6_empty_zero_page;
  76         ptrs[disks-1] = dq;
  77
  78         raid6_call.gen_syndrome(disks, bytes, ptrs);
  79
  80         /* Restore pointer table */
  81         ptrs[faila]   = dq;
  82         ptrs[disks-1] = q;
  83
  84         /* Now, pick the proper data tables */
  85         qmul  = raid6_gfmul[raid6_gfinv[raid6_gfexp[faila]]];
  86
  87         /* Now do it... */
  88         while ( bytes-- ) {
  89                 *p++ ^= *dq = qmul[*q ^ *dq];
  90                 q++; dq++;
  91         }
  92 }
  93
  94
  95 const struct raid6_recov_calls raid6_recov_intx1 = {
  96         .data2 = raid6_2data_recov_intx1,
  97         .datap = raid6_datap_recov_intx1,
  98         .valid = NULL,
  99         .name = "intx1",
 100         .priority = 0,
 101 };
 102
 103 #ifndef __KERNEL__
 104 /* Testing only */
 105
 106 /* Recover two failed blocks. */
 107 void raid6_dual_recov(int disks, size_t bytes, int faila, int failb, void **ptrs)
 108 {
 109         if ( faila > failb ) {
 110                 int tmp = faila;
 111                 faila = failb;
 112                 failb = tmp;
 113         }
 114
 115         if ( failb == disks-1 ) {
 116                 if ( faila == disks-2 ) {
 117                         /* P+Q failure.  Just rebuild the syndrome. */
 118                         raid6_call.gen_syndrome(disks, bytes, ptrs);
 119                 } else {
 120                         /* data+Q failure.  Reconstruct data from P,
 121                            then rebuild syndrome. */
 122                         /* NOT IMPLEMENTED - equivalent to RAID-5 */
 123                 }
 124         } else {
 125                 if ( failb == disks-2 ) {
 126                         /* data+P failure. */
 127                         raid6_datap_recov(disks, bytes, faila, ptrs);
 128                 } else {
 129                         /* data+data failure. */
 130                         raid6_2data_recov(disks, bytes, faila, failb, ptrs);
 131                 }
 132         }
 133 }
 134
 135 #endif