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raid6recov.c
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raid6recov.c
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/* -*- linux-c -*- ------------------------------------------------------- *
*
* Copyright 2002 H. Peter Anvin - All Rights Reserved
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation, Inc., 53 Temple Place Ste 330,
* Bostom MA 02111-1307, USA; either version 2 of the License, or
* (at your option) any later version; incorporated herein by reference.
*
* ----------------------------------------------------------------------- */
/*
* raid6recov.c
*
* RAID-6 data recovery in dual failure mode. In single failure mode,
* use the RAID-5 algorithm (or, in the case of Q failure, just reconstruct
* the syndrome.)
*/
#include "raid6.h"
/* Recover two failed data blocks. */
void raid6_2data_recov(int disks, size_t bytes, int faila, int failb,
void **ptrs)
{
u8 *p, *q, *dp, *dq;
u8 px, qx, db;
const u8 *pbmul; /* P multiplier table for B data */
const u8 *qmul; /* Q multiplier table (for both) */
p = (u8 *)ptrs[disks-2];
q = (u8 *)ptrs[disks-1];
/* Compute syndrome with zero for the missing data pages
Use the dead data pages as temporary storage for
delta p and delta q */
dp = (u8 *)ptrs[faila];
ptrs[faila] = (void *)raid6_empty_zero_page;
ptrs[disks-2] = dp;
dq = (u8 *)ptrs[failb];
ptrs[failb] = (void *)raid6_empty_zero_page;
ptrs[disks-1] = dq;
raid6_call.gen_syndrome(disks, bytes, ptrs);
/* Restore pointer table */
ptrs[faila] = dp;
ptrs[failb] = dq;
ptrs[disks-2] = p;
ptrs[disks-1] = q;
/* Now, pick the proper data tables */
pbmul = raid6_gfmul[raid6_gfexi[failb-faila]];
qmul = raid6_gfmul[raid6_gfinv[raid6_gfexp[faila]^raid6_gfexp[failb]]];
/* Now do it... */
while ( bytes-- ) {
px = *p ^ *dp;
qx = qmul[*q ^ *dq];
*dq++ = db = pbmul[px] ^ qx; /* Reconstructed B */
*dp++ = db ^ px; /* Reconstructed A */
p++; q++;
}
}
/* Recover failure of one data block plus the P block */
void raid6_datap_recov(int disks, size_t bytes, int faila, void **ptrs)
{
u8 *p, *q, *dq;
const u8 *qmul; /* Q multiplier table */
p = (u8 *)ptrs[disks-2];
q = (u8 *)ptrs[disks-1];
/* Compute syndrome with zero for the missing data page
Use the dead data page as temporary storage for delta q */
dq = (u8 *)ptrs[faila];
ptrs[faila] = (void *)raid6_empty_zero_page;
ptrs[disks-1] = dq;
raid6_call.gen_syndrome(disks, bytes, ptrs);
/* Restore pointer table */
ptrs[faila] = dq;
ptrs[disks-1] = q;
/* Now, pick the proper data tables */
qmul = raid6_gfmul[raid6_gfinv[raid6_gfexp[faila]]];
/* Now do it... */
while ( bytes-- ) {
*p++ ^= *dq = qmul[*q ^ *dq];
q++; dq++;
}
}
#ifndef __KERNEL__ /* Testing only */
/* Recover two failed blocks. */
void raid6_dual_recov(int disks, size_t bytes, int faila, int failb, void **ptrs)
{
if ( faila > failb ) {
int tmp = faila;
faila = failb;
failb = tmp;
}
if ( failb == disks-1 ) {
if ( faila == disks-2 ) {
/* P+Q failure. Just rebuild the syndrome. */
raid6_call.gen_syndrome(disks, bytes, ptrs);
} else {
/* data+Q failure. Reconstruct data from P,
then rebuild syndrome. */
/* NOT IMPLEMENTED - equivalent to RAID-5 */
}
} else {
if ( failb == disks-2 ) {
/* data+P failure. */
raid6_datap_recov(disks, bytes, faila, ptrs);
} else {
/* data+data failure. */
raid6_2data_recov(disks, bytes, faila, failb, ptrs);
}
}
}
#endif