LXR linux/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. */
  20static 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 */
  64static 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
  96const 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. */
 108void 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
 137