1 /* -*- mode: c; c-basic-offset: 8; -*-
2 * vim: noexpandtab sw=8 ts=8 sts=0:
6 * Checksum and ECC codes for the OCFS2 userspace library.
8 * Copyright (C) 2006, 2008 Oracle. All rights reserved.
10 * This program is free software; you can redistribute it and/or
11 * modify it under the terms of the GNU General Public
12 * License, version 2, as published by the Free Software Foundation.
14 * This program is distributed in the hope that it will be useful,
15 * but WITHOUT ANY WARRANTY; without even the implied warranty of
16 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
17 * General Public License for more details.
20 #include <linux/kernel.h>
21 #include <linux/types.h>
22 #include <linux/crc32.h>
23 #include <linux/buffer_head.h>
24 #include <linux/bitops.h>
25 #include <asm/byteorder.h>
27 #include <cluster/masklog.h>
31 #include "blockcheck.h"
36 * We use the following conventions:
40 * c = # total code bits (d + p)
42 static int calc_parity_bits(unsigned int d)
47 * Bits required for Single Error Correction is as follows:
51 * We're restricting ourselves to 31 bits of parity, that should be
54 for (p = 1; p < 32; p++)
56 if ((d + p + 1) <= (1 << p))
64 * Calculate the bit offset in the hamming code buffer based on the bit's
65 * offset in the data buffer. Since the hamming code reserves all
66 * power-of-two bits for parity, the data bit number and the code bit
67 * number are offest by all the parity bits beforehand.
69 * Recall that bit numbers in hamming code are 1-based. This function
70 * takes the 0-based data bit from the caller.
72 * An example. Take bit 1 of the data buffer. 1 is a power of two (2^0),
73 * so it's a parity bit. 2 is a power of two (2^1), so it's a parity bit.
74 * 3 is not a power of two. So bit 1 of the data buffer ends up as bit 3
77 static unsigned int calc_code_bit(unsigned int i)
82 * Data bits are 0-based, but we're talking code bits, which
88 * For every power of two below our bit number, bump our bit.
90 * We compare with (b + 1) becuase we have to compare with what b
91 * would be _if_ it were bumped up by the parity bit. Capice?
93 for (p = 0; (1 << p) < (b + 1); p++)
100 * This is the low level encoder function. It can be called across
101 * multiple hunks just like the crc32 code. 'd' is the number of bits
102 * _in_this_hunk_. nr is the bit offset of this hunk. So, if you had
103 * two 512B buffers, you would do it like so:
105 * parity = ocfs2_hamming_encode(0, buf1, 512 * 8, 0);
106 * parity = ocfs2_hamming_encode(parity, buf2, 512 * 8, 512 * 8);
108 * If you just have one buffer, use ocfs2_hamming_encode_block().
110 u32 ocfs2_hamming_encode(u32 parity, void *data, unsigned int d, unsigned int nr)
112 unsigned int p = calc_parity_bits(nr + d);
113 unsigned int i, j, b;
118 * b is the hamming code bit number. Hamming code specifies a
119 * 1-based array, but C uses 0-based. So 'i' is for C, and 'b' is
122 * The i++ in the for loop is so that the start offset passed
123 * to ocfs2_find_next_bit_set() is one greater than the previously
126 for (i = 0; (i = ocfs2_find_next_bit(data, d, i)) < d; i++)
129 * i is the offset in this hunk, nr + i is the total bit
132 b = calc_code_bit(nr + i);
134 for (j = 0; j < p; j++)
137 * Data bits in the resultant code are checked by
138 * parity bits that are part of the bit number
139 * representation. Huh?
141 * <wikipedia href="http://en.wikipedia.org/wiki/Hamming_code">
142 * In other words, the parity bit at position 2^k
143 * checks bits in positions having bit k set in
144 * their binary representation. Conversely, for
145 * instance, bit 13, i.e. 1101(2), is checked by
146 * bits 1000(2) = 8, 0100(2)=4 and 0001(2) = 1.
149 * Note that 'k' is the _code_ bit number. 'b' in
157 /* While the data buffer was treated as little endian, the
158 * return value is in host endian. */
162 u32 ocfs2_hamming_encode_block(void *data, unsigned int blocksize)
164 return ocfs2_hamming_encode(0, data, blocksize * 8, 0);
168 * Like ocfs2_hamming_encode(), this can handle hunks. nr is the bit
169 * offset of the current hunk. If bit to be fixed is not part of the
170 * current hunk, this does nothing.
172 * If you only have one hunk, use ocfs2_hamming_fix_block().
174 void ocfs2_hamming_fix(void *data, unsigned int d, unsigned int nr,
177 unsigned int p = calc_parity_bits(nr + d);
183 * If the bit to fix has an hweight of 1, it's a parity bit. One
184 * busted parity bit is its own error. Nothing to do here.
186 if (hweight32(fix) == 1)
190 * nr + d is the bit right past the data hunk we're looking at.
191 * If fix after that, nothing to do
193 if (fix >= calc_code_bit(nr + d))
197 * nr is the offset in the data hunk we're starting at. Let's
198 * start b at the offset in the code buffer. See hamming_encode()
199 * for a more detailed description of 'b'.
201 b = calc_code_bit(nr);
202 /* If the fix is before this hunk, nothing to do */
206 for (i = 0; i < d; i++, b++)
208 /* Skip past parity bits */
209 while (hweight32(b) == 1)
213 * i is the offset in this data hunk.
214 * nr + i is the offset in the total data buffer.
215 * b is the offset in the total code buffer.
217 * Thus, when b == fix, bit i in the current hunk needs
222 if (ocfs2_test_bit(i, data))
223 ocfs2_clear_bit(i, data);
225 ocfs2_set_bit(i, data);
231 void ocfs2_hamming_fix_block(void *data, unsigned int blocksize,
234 ocfs2_hamming_fix(data, blocksize * 8, 0, fix);
238 * This function generates check information for a block.
239 * data is the block to be checked. bc is a pointer to the
240 * ocfs2_block_check structure describing the crc32 and the ecc.
242 * bc should be a pointer inside data, as the function will
243 * take care of zeroing it before calculating the check information. If
244 * bc does not point inside data, the caller must make sure any inline
245 * ocfs2_block_check structures are zeroed.
247 * The data buffer must be in on-disk endian (little endian for ocfs2).
248 * bc will be filled with little-endian values and will be ready to go to
251 void ocfs2_block_check_compute(void *data, size_t blocksize,
252 struct ocfs2_block_check *bc)
257 memset(bc, 0, sizeof(struct ocfs2_block_check));
259 crc = crc32_le(~0, data, blocksize);
260 ecc = ocfs2_hamming_encode_block(data, blocksize);
263 * No ecc'd ocfs2 structure is larger than 4K, so ecc will be no
264 * larger than 16 bits.
266 BUG_ON(ecc > USHORT_MAX);
268 bc->bc_crc32e = cpu_to_le32(crc);
269 bc->bc_ecc = cpu_to_le16((u16)ecc);
273 * This function validates existing check information. Like _compute,
274 * the function will take care of zeroing bc before calculating check codes.
275 * If bc is not a pointer inside data, the caller must have zeroed any
276 * inline ocfs2_block_check structures.
278 * Again, the data passed in should be the on-disk endian.
280 int ocfs2_block_check_validate(void *data, size_t blocksize,
281 struct ocfs2_block_check *bc)
284 struct ocfs2_block_check check;
287 check.bc_crc32e = le32_to_cpu(bc->bc_crc32e);
288 check.bc_ecc = le16_to_cpu(bc->bc_ecc);
290 memset(bc, 0, sizeof(struct ocfs2_block_check));
292 /* Fast path - if the crc32 validates, we're good to go */
293 crc = crc32_le(~0, data, blocksize);
294 if (crc == check.bc_crc32e)
298 "CRC32 failed: stored: %u, computed %u. Applying ECC.\n",
299 (unsigned int)check.bc_crc32e, (unsigned int)crc);
301 /* Ok, try ECC fixups */
302 ecc = ocfs2_hamming_encode_block(data, blocksize);
303 ocfs2_hamming_fix_block(data, blocksize, ecc ^ check.bc_ecc);
305 /* And check the crc32 again */
306 crc = crc32_le(~0, data, blocksize);
307 if (crc == check.bc_crc32e)
310 mlog(ML_ERROR, "Fixed CRC32 failed: stored: %u, computed %u\n",
311 (unsigned int)check.bc_crc32e, (unsigned int)crc);
316 bc->bc_crc32e = cpu_to_le32(check.bc_crc32e);
317 bc->bc_ecc = cpu_to_le16(check.bc_ecc);
323 * This function generates check information for a list of buffer_heads.
324 * bhs is the blocks to be checked. bc is a pointer to the
325 * ocfs2_block_check structure describing the crc32 and the ecc.
327 * bc should be a pointer inside data, as the function will
328 * take care of zeroing it before calculating the check information. If
329 * bc does not point inside data, the caller must make sure any inline
330 * ocfs2_block_check structures are zeroed.
332 * The data buffer must be in on-disk endian (little endian for ocfs2).
333 * bc will be filled with little-endian values and will be ready to go to
336 void ocfs2_block_check_compute_bhs(struct buffer_head **bhs, int nr,
337 struct ocfs2_block_check *bc)
347 memset(bc, 0, sizeof(struct ocfs2_block_check));
349 for (i = 0, crc = ~0, ecc = 0; i < nr; i++) {
350 crc = crc32_le(crc, bhs[i]->b_data, bhs[i]->b_size);
352 * The number of bits in a buffer is obviously b_size*8.
353 * The offset of this buffer is b_size*i, so the bit offset
354 * of this buffer is b_size*8*i.
356 ecc = (u16)ocfs2_hamming_encode(ecc, bhs[i]->b_data,
358 bhs[i]->b_size * 8 * i);
362 * No ecc'd ocfs2 structure is larger than 4K, so ecc will be no
363 * larger than 16 bits.
365 BUG_ON(ecc > USHORT_MAX);
367 bc->bc_crc32e = cpu_to_le32(crc);
368 bc->bc_ecc = cpu_to_le16((u16)ecc);
372 * This function validates existing check information on a list of
373 * buffer_heads. Like _compute_bhs, the function will take care of
374 * zeroing bc before calculating check codes. If bc is not a pointer
375 * inside data, the caller must have zeroed any inline
376 * ocfs2_block_check structures.
378 * Again, the data passed in should be the on-disk endian.
380 int ocfs2_block_check_validate_bhs(struct buffer_head **bhs, int nr,
381 struct ocfs2_block_check *bc)
384 struct ocfs2_block_check check;
392 check.bc_crc32e = le32_to_cpu(bc->bc_crc32e);
393 check.bc_ecc = le16_to_cpu(bc->bc_ecc);
395 memset(bc, 0, sizeof(struct ocfs2_block_check));
397 /* Fast path - if the crc32 validates, we're good to go */
398 for (i = 0, crc = ~0; i < nr; i++)
399 crc = crc32_le(crc, bhs[i]->b_data, bhs[i]->b_size);
400 if (crc == check.bc_crc32e)
404 "CRC32 failed: stored: %u, computed %u. Applying ECC.\n",
405 (unsigned int)check.bc_crc32e, (unsigned int)crc);
407 /* Ok, try ECC fixups */
408 for (i = 0, ecc = 0; i < nr; i++) {
410 * The number of bits in a buffer is obviously b_size*8.
411 * The offset of this buffer is b_size*i, so the bit offset
412 * of this buffer is b_size*8*i.
414 ecc = (u16)ocfs2_hamming_encode(ecc, bhs[i]->b_data,
416 bhs[i]->b_size * 8 * i);
418 fix = ecc ^ check.bc_ecc;
419 for (i = 0; i < nr; i++) {
421 * Try the fix against each buffer. It will only affect
424 ocfs2_hamming_fix(bhs[i]->b_data, bhs[i]->b_size * 8,
425 bhs[i]->b_size * 8 * i, fix);
428 /* And check the crc32 again */
429 for (i = 0, crc = ~0; i < nr; i++)
430 crc = crc32_le(crc, bhs[i]->b_data, bhs[i]->b_size);
431 if (crc == check.bc_crc32e)
434 mlog(ML_ERROR, "Fixed CRC32 failed: stored: %u, computed %u\n",
435 (unsigned int)check.bc_crc32e, (unsigned int)crc);
440 bc->bc_crc32e = cpu_to_le32(check.bc_crc32e);
441 bc->bc_ecc = cpu_to_le16(check.bc_ecc);
447 * These are the main API. They check the superblock flag before
448 * calling the underlying operations.
450 * They expect the buffer(s) to be in disk format.
452 void ocfs2_compute_meta_ecc(struct super_block *sb, void *data,
453 struct ocfs2_block_check *bc)
455 if (ocfs2_meta_ecc(OCFS2_SB(sb)))
456 ocfs2_block_check_compute(data, sb->s_blocksize, bc);
459 int ocfs2_validate_meta_ecc(struct super_block *sb, void *data,
460 struct ocfs2_block_check *bc)
464 if (ocfs2_meta_ecc(OCFS2_SB(sb)))
465 rc = ocfs2_block_check_validate(data, sb->s_blocksize, bc);
470 void ocfs2_compute_meta_ecc_bhs(struct super_block *sb,
471 struct buffer_head **bhs, int nr,
472 struct ocfs2_block_check *bc)
474 if (ocfs2_meta_ecc(OCFS2_SB(sb)))
475 ocfs2_block_check_compute_bhs(bhs, nr, bc);
478 int ocfs2_validate_meta_ecc_bhs(struct super_block *sb,
479 struct buffer_head **bhs, int nr,
480 struct ocfs2_block_check *bc)
484 if (ocfs2_meta_ecc(OCFS2_SB(sb)))
485 rc = ocfs2_block_check_validate_bhs(bhs, nr, bc);