// SPDX-License-Identifier: GPL-2.0-or-later
/* -*- linux-c -*- ------------------------------------------------------- *
 *
 *   Copyright 2002 H. Peter Anvin - All Rights Reserved
 *
 * ----------------------------------------------------------------------- */

/*
 * 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/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] = raid6_get_zero_page();
        ptrs[disks-2] = dp;
        dq = (u8 *)ptrs[failb];
        ptrs[failb] = raid6_get_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] = raid6_get_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