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. */
24 void 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 */
71 void 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. */
105 void 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
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