recov.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,
 *   Boston MA 02111-1307, USA; either version 2 of the License, or
 *   (at your option) any later version; incorporated herein by reference.
 *
 * ----------------------------------------------------------------------- */

/*
 * raid6/recov.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 <linux/export.h>
#include <linux/raid/pq.h>

/* Recover two failed data blocks. */
static void raid6_2data_recov_intx1(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 */
static void raid6_datap_recov_intx1(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++;
    }
}


const struct raid6_recov_calls raid6_recov_intx1 = {
    .data2 = raid6_2data_recov_intx1,
    .datap = raid6_datap_recov_intx1,
    .valid = NULL,
    .name = "intx1",
    .priority = 0,
};

#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