1/* -*- linux-c -*- ------------------------------------------------------- *
2 *
3 *   Copyright 2002 H. Peter Anvin - All Rights Reserved
4 *
5 *   This program is free software; you can redistribute it and/or modify
6 *   it under the terms of the GNU General Public License as published by
7 *   the Free Software Foundation, Inc., 53 Temple Place Ste 330,
8 *   Bostom MA 02111-1307, USA; either version 2 of the License, or
9 *   (at your option) any later version; incorporated herein by reference.
10 *
11 * ----------------------------------------------------------------------- */
12
13/*
14 * raid6recov.c
15 *
16 * RAID-6 data recovery in dual failure mode.  In single failure mode,
17 * use the RAID-5 algorithm (or, in the case of Q failure, just reconstruct
18 * the syndrome.)
19 */
20
21#include "raid6.h"
22
23/* Recover two failed data blocks. */
24void raid6_2data_recov(int disks, size_t bytes, int faila, int failb,
25		       void **ptrs)
26{
27	u8 *p, *q, *dp, *dq;
28	u8 px, qx, db;
29	const u8 *pbmul;	/* P multiplier table for B data */
30	const u8 *qmul;		/* Q multiplier table (for both) */
31
32	p = (u8 *)ptrs[disks-2];
33	q = (u8 *)ptrs[disks-1];
34
35	/* Compute syndrome with zero for the missing data pages
36	   Use the dead data pages as temporary storage for
37	   delta p and delta q */
38	dp = (u8 *)ptrs[faila];
39	ptrs[faila] = (void *)raid6_empty_zero_page;
40	ptrs[disks-2] = dp;
41	dq = (u8 *)ptrs[failb];
42	ptrs[failb] = (void *)raid6_empty_zero_page;
43	ptrs[disks-1] = dq;
44
45	raid6_call.gen_syndrome(disks, bytes, ptrs);
46
47	/* Restore pointer table */
48	ptrs[faila]   = dp;
49	ptrs[failb]   = dq;
50	ptrs[disks-2] = p;
51	ptrs[disks-1] = q;
52
53	/* Now, pick the proper data tables */
54	pbmul = raid6_gfmul[raid6_gfexi[failb-faila]];
55	qmul  = raid6_gfmul[raid6_gfinv[raid6_gfexp[faila]^raid6_gfexp[failb]]];
56
57	/* Now do it... */
58	while ( bytes-- ) {
59		px    = *p ^ *dp;
60		qx    = qmul[*q ^ *dq];
61		*dq++ = db = pbmul[px] ^ qx; /* Reconstructed B */
62		*dp++ = db ^ px; /* Reconstructed A */
63		p++; q++;
64	}
65}
66
67
68
69
70/* Recover failure of one data block plus the P block */
71void raid6_datap_recov(int disks, size_t bytes, int faila, void **ptrs)
72{
73	u8 *p, *q, *dq;
74	const u8 *qmul;		/* Q multiplier table */
75
76	p = (u8 *)ptrs[disks-2];
77	q = (u8 *)ptrs[disks-1];
78
79	/* Compute syndrome with zero for the missing data page
80	   Use the dead data page as temporary storage for delta q */
81	dq = (u8 *)ptrs[faila];
82	ptrs[faila] = (void *)raid6_empty_zero_page;
83	ptrs[disks-1] = dq;
84
85	raid6_call.gen_syndrome(disks, bytes, ptrs);
86
87	/* Restore pointer table */
88	ptrs[faila]   = dq;
89	ptrs[disks-1] = q;
90
91	/* Now, pick the proper data tables */
92	qmul  = raid6_gfmul[raid6_gfinv[raid6_gfexp[faila]]];
93
94	/* Now do it... */
95	while ( bytes-- ) {
96		*p++ ^= *dq = qmul[*q ^ *dq];
97		q++; dq++;
98	}
99}
100
101
102#ifndef __KERNEL__		    /* Testing only */
103
104/* Recover two failed blocks. */
105void raid6_dual_recov(int disks, size_t bytes, int faila, int failb, void **ptrs)
106{
107	if ( faila > failb ) {
108		int tmp = faila;
109		faila = failb;
110		failb = tmp;
111	}
112
113	if ( failb == disks-1 ) {
114		if ( faila == disks-2 ) {
115			/* P+Q failure.  Just rebuild the syndrome. */
116			raid6_call.gen_syndrome(disks, bytes, ptrs);
117		} else {
118			/* data+Q failure.  Reconstruct data from P,
119			   then rebuild syndrome. */
120			/* NOT IMPLEMENTED - equivalent to RAID-5 */
121		}
122	} else {
123		if ( failb == disks-2 ) {
124			/* data+P failure. */
125			raid6_datap_recov(disks, bytes, faila, ptrs);
126		} else {
127			/* data+data failure. */
128			raid6_2data_recov(disks, bytes, faila, failb, ptrs);
129		}
130	}
131}
132
133#endif
134