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