summaryrefslogtreecommitdiff
path: root/fs/ocfs2/blockcheck.c
blob: 2ce6ae5e4b8ccdd9ff69bcfc3d00aa6ccfa8cd8a (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
/* -*- mode: c; c-basic-offset: 8; -*-
 * vim: noexpandtab sw=8 ts=8 sts=0:
 *
 * blockcheck.c
 *
 * Checksum and ECC codes for the OCFS2 userspace library.
 *
 * Copyright (C) 2006, 2008 Oracle.  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, version 2, as published by the Free Software Foundation.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * General Public License for more details.
 */

#include <linux/kernel.h>
#include <linux/types.h>
#include <linux/crc32.h>
#include <linux/buffer_head.h>
#include <linux/bitops.h>
#include <asm/byteorder.h>

#include <cluster/masklog.h>

#include "ocfs2.h"

#include "blockcheck.h"



/*
 * We use the following conventions:
 *
 * d = # data bits
 * p = # parity bits
 * c = # total code bits (d + p)
 */
static int calc_parity_bits(unsigned int d)
{
	unsigned int p;

	/*
	 * Bits required for Single Error Correction is as follows:
	 *
	 * d + p + 1 <= 2^p
	 *
	 * We're restricting ourselves to 31 bits of parity, that should be
	 * sufficient.
	 */
	for (p = 1; p < 32; p++)
	{
		if ((d + p + 1) <= (1 << p))
			return p;
	}

	return 0;
}

/*
 * Calculate the bit offset in the hamming code buffer based on the bit's
 * offset in the data buffer.  Since the hamming code reserves all
 * power-of-two bits for parity, the data bit number and the code bit
 * number are offest by all the parity bits beforehand.
 *
 * Recall that bit numbers in hamming code are 1-based.  This function
 * takes the 0-based data bit from the caller.
 *
 * An example.  Take bit 1 of the data buffer.  1 is a power of two (2^0),
 * so it's a parity bit.  2 is a power of two (2^1), so it's a parity bit.
 * 3 is not a power of two.  So bit 1 of the data buffer ends up as bit 3
 * in the code buffer.
 */
static unsigned int calc_code_bit(unsigned int i)
{
	unsigned int b, p;

	/*
	 * Data bits are 0-based, but we're talking code bits, which
	 * are 1-based.
	 */
	b = i + 1;

	/*
	 * For every power of two below our bit number, bump our bit.
	 *
	 * We compare with (b + 1) becuase we have to compare with what b
	 * would be _if_ it were bumped up by the parity bit.  Capice?
	 */
	for (p = 0; (1 << p) < (b + 1); p++)
		b++;

	return b;
}

/*
 * This is the low level encoder function.  It can be called across
 * multiple hunks just like the crc32 code.  'd' is the number of bits
 * _in_this_hunk_.  nr is the bit offset of this hunk.  So, if you had
 * two 512B buffers, you would do it like so:
 *
 * parity = ocfs2_hamming_encode(0, buf1, 512 * 8, 0);
 * parity = ocfs2_hamming_encode(parity, buf2, 512 * 8, 512 * 8);
 *
 * If you just have one buffer, use ocfs2_hamming_encode_block().
 */
u32 ocfs2_hamming_encode(u32 parity, void *data, unsigned int d, unsigned int nr)
{
	unsigned int p = calc_parity_bits(nr + d);
	unsigned int i, j, b;

	BUG_ON(!p);

	/*
	 * b is the hamming code bit number.  Hamming code specifies a
	 * 1-based array, but C uses 0-based.  So 'i' is for C, and 'b' is
	 * for the algorithm.
	 *
	 * The i++ in the for loop is so that the start offset passed
	 * to ocfs2_find_next_bit_set() is one greater than the previously
	 * found bit.
	 */
	for (i = 0; (i = ocfs2_find_next_bit(data, d, i)) < d; i++)
	{
		/*
		 * i is the offset in this hunk, nr + i is the total bit
		 * offset.
		 */
		b = calc_code_bit(nr + i);

		for (j = 0; j < p; j++)
		{
			/*
			 * Data bits in the resultant code are checked by
			 * parity bits that are part of the bit number
			 * representation.  Huh?
			 *
			 * <wikipedia href="http://en.wikipedia.org/wiki/Hamming_code">
			 * In other words, the parity bit at position 2^k
			 * checks bits in positions having bit k set in
			 * their binary representation.  Conversely, for
			 * instance, bit 13, i.e. 1101(2), is checked by
			 * bits 1000(2) = 8, 0100(2)=4 and 0001(2) = 1.
			 * </wikipedia>
			 *
			 * Note that 'k' is the _code_ bit number.  'b' in
			 * our loop.
			 */
			if (b & (1 << j))
				parity ^= (1 << j);
		}
	}

	/* While the data buffer was treated as little endian, the
	 * return value is in host endian. */
	return parity;
}

u32 ocfs2_hamming_encode_block(void *data, unsigned int blocksize)
{
	return ocfs2_hamming_encode(0, data, blocksize * 8, 0);
}

/*
 * Like ocfs2_hamming_encode(), this can handle hunks.  nr is the bit
 * offset of the current hunk.  If bit to be fixed is not part of the
 * current hunk, this does nothing.
 *
 * If you only have one hunk, use ocfs2_hamming_fix_block().
 */
void ocfs2_hamming_fix(void *data, unsigned int d, unsigned int nr,
		       unsigned int fix)
{
	unsigned int p = calc_parity_bits(nr + d);
	unsigned int i, b;

	BUG_ON(!p);

	/*
	 * If the bit to fix has an hweight of 1, it's a parity bit.  One
	 * busted parity bit is its own error.  Nothing to do here.
	 */
	if (hweight32(fix) == 1)
		return;

	/*
	 * nr + d is the bit right past the data hunk we're looking at.
	 * If fix after that, nothing to do
	 */
	if (fix >= calc_code_bit(nr + d))
		return;

	/*
	 * nr is the offset in the data hunk we're starting at.  Let's
	 * start b at the offset in the code buffer.  See hamming_encode()
	 * for a more detailed description of 'b'.
	 */
	b = calc_code_bit(nr);
	/* If the fix is before this hunk, nothing to do */
	if (fix < b)
		return;

	for (i = 0; i < d; i++, b++)
	{
		/* Skip past parity bits */
		while (hweight32(b) == 1)
			b++;

		/*
		 * i is the offset in this data hunk.
		 * nr + i is the offset in the total data buffer.
		 * b is the offset in the total code buffer.
		 *
		 * Thus, when b == fix, bit i in the current hunk needs
		 * fixing.
		 */
		if (b == fix)
		{
			if (ocfs2_test_bit(i, data))
				ocfs2_clear_bit(i, data);
			else
				ocfs2_set_bit(i, data);
			break;
		}
	}
}

void ocfs2_hamming_fix_block(void *data, unsigned int blocksize,
			     unsigned int fix)
{
	ocfs2_hamming_fix(data, blocksize * 8, 0, fix);
}

/*
 * This function generates check information for a block.
 * data is the block to be checked.  bc is a pointer to the
 * ocfs2_block_check structure describing the crc32 and the ecc.
 *
 * bc should be a pointer inside data, as the function will
 * take care of zeroing it before calculating the check information.  If
 * bc does not point inside data, the caller must make sure any inline
 * ocfs2_block_check structures are zeroed.
 *
 * The data buffer must be in on-disk endian (little endian for ocfs2).
 * bc will be filled with little-endian values and will be ready to go to
 * disk.
 */
void ocfs2_block_check_compute(void *data, size_t blocksize,
			       struct ocfs2_block_check *bc)
{
	u32 crc;
	u32 ecc;

	memset(bc, 0, sizeof(struct ocfs2_block_check));

	crc = crc32_le(~0, data, blocksize);
	ecc = ocfs2_hamming_encode_block(data, blocksize);

	/*
	 * No ecc'd ocfs2 structure is larger than 4K, so ecc will be no
	 * larger than 16 bits.
	 */
	BUG_ON(ecc > USHORT_MAX);

	bc->bc_crc32e = cpu_to_le32(crc);
	bc->bc_ecc = cpu_to_le16((u16)ecc);
}

/*
 * This function validates existing check information.  Like _compute,
 * the function will take care of zeroing bc before calculating check codes.
 * If bc is not a pointer inside data, the caller must have zeroed any
 * inline ocfs2_block_check structures.
 *
 * Again, the data passed in should be the on-disk endian.
 */
int ocfs2_block_check_validate(void *data, size_t blocksize,
			       struct ocfs2_block_check *bc)
{
	int rc = 0;
	struct ocfs2_block_check check;
	u32 crc, ecc;

	check.bc_crc32e = le32_to_cpu(bc->bc_crc32e);
	check.bc_ecc = le16_to_cpu(bc->bc_ecc);

	memset(bc, 0, sizeof(struct ocfs2_block_check));

	/* Fast path - if the crc32 validates, we're good to go */
	crc = crc32_le(~0, data, blocksize);
	if (crc == check.bc_crc32e)
		goto out;

	mlog(ML_ERROR,
	     "CRC32 failed: stored: %u, computed %u.  Applying ECC.\n",
	     (unsigned int)check.bc_crc32e, (unsigned int)crc);

	/* Ok, try ECC fixups */
	ecc = ocfs2_hamming_encode_block(data, blocksize);
	ocfs2_hamming_fix_block(data, blocksize, ecc ^ check.bc_ecc);

	/* And check the crc32 again */
	crc = crc32_le(~0, data, blocksize);
	if (crc == check.bc_crc32e)
		goto out;

	mlog(ML_ERROR, "Fixed CRC32 failed: stored: %u, computed %u\n",
	     (unsigned int)check.bc_crc32e, (unsigned int)crc);

	rc = -EIO;

out:
	bc->bc_crc32e = cpu_to_le32(check.bc_crc32e);
	bc->bc_ecc = cpu_to_le16(check.bc_ecc);

	return rc;
}

/*
 * This function generates check information for a list of buffer_heads.
 * bhs is the blocks to be checked.  bc is a pointer to the
 * ocfs2_block_check structure describing the crc32 and the ecc.
 *
 * bc should be a pointer inside data, as the function will
 * take care of zeroing it before calculating the check information.  If
 * bc does not point inside data, the caller must make sure any inline
 * ocfs2_block_check structures are zeroed.
 *
 * The data buffer must be in on-disk endian (little endian for ocfs2).
 * bc will be filled with little-endian values and will be ready to go to
 * disk.
 */
void ocfs2_block_check_compute_bhs(struct buffer_head **bhs, int nr,
				   struct ocfs2_block_check *bc)
{
	int i;
	u32 crc, ecc;

	BUG_ON(nr < 0);

	if (!nr)
		return;

	memset(bc, 0, sizeof(struct ocfs2_block_check));

	for (i = 0, crc = ~0, ecc = 0; i < nr; i++) {
		crc = crc32_le(crc, bhs[i]->b_data, bhs[i]->b_size);
		/*
		 * The number of bits in a buffer is obviously b_size*8.
		 * The offset of this buffer is b_size*i, so the bit offset
		 * of this buffer is b_size*8*i.
		 */
		ecc = (u16)ocfs2_hamming_encode(ecc, bhs[i]->b_data,
						bhs[i]->b_size * 8,
						bhs[i]->b_size * 8 * i);
	}

	/*
	 * No ecc'd ocfs2 structure is larger than 4K, so ecc will be no
	 * larger than 16 bits.
	 */
	BUG_ON(ecc > USHORT_MAX);

	bc->bc_crc32e = cpu_to_le32(crc);
	bc->bc_ecc = cpu_to_le16((u16)ecc);
}

/*
 * This function validates existing check information on a list of
 * buffer_heads.  Like _compute_bhs, the function will take care of
 * zeroing bc before calculating check codes.  If bc is not a pointer
 * inside data, the caller must have zeroed any inline
 * ocfs2_block_check structures.
 *
 * Again, the data passed in should be the on-disk endian.
 */
int ocfs2_block_check_validate_bhs(struct buffer_head **bhs, int nr,
				   struct ocfs2_block_check *bc)
{
	int i, rc = 0;
	struct ocfs2_block_check check;
	u32 crc, ecc, fix;

	BUG_ON(nr < 0);

	if (!nr)
		return 0;

	check.bc_crc32e = le32_to_cpu(bc->bc_crc32e);
	check.bc_ecc = le16_to_cpu(bc->bc_ecc);

	memset(bc, 0, sizeof(struct ocfs2_block_check));

	/* Fast path - if the crc32 validates, we're good to go */
	for (i = 0, crc = ~0; i < nr; i++)
		crc = crc32_le(crc, bhs[i]->b_data, bhs[i]->b_size);
	if (crc == check.bc_crc32e)
		goto out;

	mlog(ML_ERROR,
	     "CRC32 failed: stored: %u, computed %u.  Applying ECC.\n",
	     (unsigned int)check.bc_crc32e, (unsigned int)crc);

	/* Ok, try ECC fixups */
	for (i = 0, ecc = 0; i < nr; i++) {
		/*
		 * The number of bits in a buffer is obviously b_size*8.
		 * The offset of this buffer is b_size*i, so the bit offset
		 * of this buffer is b_size*8*i.
		 */
		ecc = (u16)ocfs2_hamming_encode(ecc, bhs[i]->b_data,
						bhs[i]->b_size * 8,
						bhs[i]->b_size * 8 * i);
	}
	fix = ecc ^ check.bc_ecc;
	for (i = 0; i < nr; i++) {
		/*
		 * Try the fix against each buffer.  It will only affect
		 * one of them.
		 */
		ocfs2_hamming_fix(bhs[i]->b_data, bhs[i]->b_size * 8,
				  bhs[i]->b_size * 8 * i, fix);
	}

	/* And check the crc32 again */
	for (i = 0, crc = ~0; i < nr; i++)
		crc = crc32_le(crc, bhs[i]->b_data, bhs[i]->b_size);
	if (crc == check.bc_crc32e)
		goto out;

	mlog(ML_ERROR, "Fixed CRC32 failed: stored: %u, computed %u\n",
	     (unsigned int)check.bc_crc32e, (unsigned int)crc);

	rc = -EIO;

out:
	bc->bc_crc32e = cpu_to_le32(check.bc_crc32e);
	bc->bc_ecc = cpu_to_le16(check.bc_ecc);

	return rc;
}

/*
 * These are the main API.  They check the superblock flag before
 * calling the underlying operations.
 *
 * They expect the buffer(s) to be in disk format.
 */
void ocfs2_compute_meta_ecc(struct super_block *sb, void *data,
			    struct ocfs2_block_check *bc)
{
	if (ocfs2_meta_ecc(OCFS2_SB(sb)))
		ocfs2_block_check_compute(data, sb->s_blocksize, bc);
}

int ocfs2_validate_meta_ecc(struct super_block *sb, void *data,
			    struct ocfs2_block_check *bc)
{
	int rc = 0;

	if (ocfs2_meta_ecc(OCFS2_SB(sb)))
		rc = ocfs2_block_check_validate(data, sb->s_blocksize, bc);

	return rc;
}

void ocfs2_compute_meta_ecc_bhs(struct super_block *sb,
				struct buffer_head **bhs, int nr,
				struct ocfs2_block_check *bc)
{
	if (ocfs2_meta_ecc(OCFS2_SB(sb)))
		ocfs2_block_check_compute_bhs(bhs, nr, bc);
}

int ocfs2_validate_meta_ecc_bhs(struct super_block *sb,
				struct buffer_head **bhs, int nr,
				struct ocfs2_block_check *bc)
{
	int rc = 0;

	if (ocfs2_meta_ecc(OCFS2_SB(sb)))
		rc = ocfs2_block_check_validate_bhs(bhs, nr, bc);

	return rc;
}