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"
35 * We use the following conventions:
39 * c = # total code bits (d + p)
43 * Calculate the bit offset in the hamming code buffer based on the bit's
44 * offset in the data buffer. Since the hamming code reserves all
45 * power-of-two bits for parity, the data bit number and the code bit
46 * number are offest by all the parity bits beforehand.
48 * Recall that bit numbers in hamming code are 1-based. This function
49 * takes the 0-based data bit from the caller.
51 * An example. Take bit 1 of the data buffer. 1 is a power of two (2^0),
52 * so it's a parity bit. 2 is a power of two (2^1), so it's a parity bit.
53 * 3 is not a power of two. So bit 1 of the data buffer ends up as bit 3
56 static unsigned int calc_code_bit(unsigned int i)
61 * Data bits are 0-based, but we're talking code bits, which
67 * For every power of two below our bit number, bump our bit.
69 * We compare with (b + 1) becuase we have to compare with what b
70 * would be _if_ it were bumped up by the parity bit. Capice?
72 for (p = 0; (1 << p) < (b + 1); p++)
79 * This is the low level encoder function. It can be called across
80 * multiple hunks just like the crc32 code. 'd' is the number of bits
81 * _in_this_hunk_. nr is the bit offset of this hunk. So, if you had
82 * two 512B buffers, you would do it like so:
84 * parity = ocfs2_hamming_encode(0, buf1, 512 * 8, 0);
85 * parity = ocfs2_hamming_encode(parity, buf2, 512 * 8, 512 * 8);
87 * If you just have one buffer, use ocfs2_hamming_encode_block().
89 u32 ocfs2_hamming_encode(u32 parity, void *data, unsigned int d, unsigned int nr)
96 * b is the hamming code bit number. Hamming code specifies a
97 * 1-based array, but C uses 0-based. So 'i' is for C, and 'b' is
100 * The i++ in the for loop is so that the start offset passed
101 * to ocfs2_find_next_bit_set() is one greater than the previously
104 for (i = 0; (i = ocfs2_find_next_bit(data, d, i)) < d; i++)
107 * i is the offset in this hunk, nr + i is the total bit
110 b = calc_code_bit(nr + i);
113 * Data bits in the resultant code are checked by
114 * parity bits that are part of the bit number
115 * representation. Huh?
117 * <wikipedia href="http://en.wikipedia.org/wiki/Hamming_code">
118 * In other words, the parity bit at position 2^k
119 * checks bits in positions having bit k set in
120 * their binary representation. Conversely, for
121 * instance, bit 13, i.e. 1101(2), is checked by
122 * bits 1000(2) = 8, 0100(2)=4 and 0001(2) = 1.
125 * Note that 'k' is the _code_ bit number. 'b' in
131 /* While the data buffer was treated as little endian, the
132 * return value is in host endian. */
136 u32 ocfs2_hamming_encode_block(void *data, unsigned int blocksize)
138 return ocfs2_hamming_encode(0, data, blocksize * 8, 0);
142 * Like ocfs2_hamming_encode(), this can handle hunks. nr is the bit
143 * offset of the current hunk. If bit to be fixed is not part of the
144 * current hunk, this does nothing.
146 * If you only have one hunk, use ocfs2_hamming_fix_block().
148 void ocfs2_hamming_fix(void *data, unsigned int d, unsigned int nr,
156 * If the bit to fix has an hweight of 1, it's a parity bit. One
157 * busted parity bit is its own error. Nothing to do here.
159 if (hweight32(fix) == 1)
163 * nr + d is the bit right past the data hunk we're looking at.
164 * If fix after that, nothing to do
166 if (fix >= calc_code_bit(nr + d))
170 * nr is the offset in the data hunk we're starting at. Let's
171 * start b at the offset in the code buffer. See hamming_encode()
172 * for a more detailed description of 'b'.
174 b = calc_code_bit(nr);
175 /* If the fix is before this hunk, nothing to do */
179 for (i = 0; i < d; i++, b++)
181 /* Skip past parity bits */
182 while (hweight32(b) == 1)
186 * i is the offset in this data hunk.
187 * nr + i is the offset in the total data buffer.
188 * b is the offset in the total code buffer.
190 * Thus, when b == fix, bit i in the current hunk needs
195 if (ocfs2_test_bit(i, data))
196 ocfs2_clear_bit(i, data);
198 ocfs2_set_bit(i, data);
204 void ocfs2_hamming_fix_block(void *data, unsigned int blocksize,
207 ocfs2_hamming_fix(data, blocksize * 8, 0, fix);
211 * This function generates check information for a block.
212 * data is the block to be checked. bc is a pointer to the
213 * ocfs2_block_check structure describing the crc32 and the ecc.
215 * bc should be a pointer inside data, as the function will
216 * take care of zeroing it before calculating the check information. If
217 * bc does not point inside data, the caller must make sure any inline
218 * ocfs2_block_check structures are zeroed.
220 * The data buffer must be in on-disk endian (little endian for ocfs2).
221 * bc will be filled with little-endian values and will be ready to go to
224 void ocfs2_block_check_compute(void *data, size_t blocksize,
225 struct ocfs2_block_check *bc)
230 memset(bc, 0, sizeof(struct ocfs2_block_check));
232 crc = crc32_le(~0, data, blocksize);
233 ecc = ocfs2_hamming_encode_block(data, blocksize);
236 * No ecc'd ocfs2 structure is larger than 4K, so ecc will be no
237 * larger than 16 bits.
239 BUG_ON(ecc > USHORT_MAX);
241 bc->bc_crc32e = cpu_to_le32(crc);
242 bc->bc_ecc = cpu_to_le16((u16)ecc);
246 * This function validates existing check information. Like _compute,
247 * the function will take care of zeroing bc before calculating check codes.
248 * If bc is not a pointer inside data, the caller must have zeroed any
249 * inline ocfs2_block_check structures.
251 * Again, the data passed in should be the on-disk endian.
253 int ocfs2_block_check_validate(void *data, size_t blocksize,
254 struct ocfs2_block_check *bc)
257 struct ocfs2_block_check check;
260 check.bc_crc32e = le32_to_cpu(bc->bc_crc32e);
261 check.bc_ecc = le16_to_cpu(bc->bc_ecc);
263 memset(bc, 0, sizeof(struct ocfs2_block_check));
265 /* Fast path - if the crc32 validates, we're good to go */
266 crc = crc32_le(~0, data, blocksize);
267 if (crc == check.bc_crc32e)
271 "CRC32 failed: stored: %u, computed %u. Applying ECC.\n",
272 (unsigned int)check.bc_crc32e, (unsigned int)crc);
274 /* Ok, try ECC fixups */
275 ecc = ocfs2_hamming_encode_block(data, blocksize);
276 ocfs2_hamming_fix_block(data, blocksize, ecc ^ check.bc_ecc);
278 /* And check the crc32 again */
279 crc = crc32_le(~0, data, blocksize);
280 if (crc == check.bc_crc32e)
283 mlog(ML_ERROR, "Fixed CRC32 failed: stored: %u, computed %u\n",
284 (unsigned int)check.bc_crc32e, (unsigned int)crc);
289 bc->bc_crc32e = cpu_to_le32(check.bc_crc32e);
290 bc->bc_ecc = cpu_to_le16(check.bc_ecc);
296 * This function generates check information for a list of buffer_heads.
297 * bhs is the blocks to be checked. bc is a pointer to the
298 * ocfs2_block_check structure describing the crc32 and the ecc.
300 * bc should be a pointer inside data, as the function will
301 * take care of zeroing it before calculating the check information. If
302 * bc does not point inside data, the caller must make sure any inline
303 * ocfs2_block_check structures are zeroed.
305 * The data buffer must be in on-disk endian (little endian for ocfs2).
306 * bc will be filled with little-endian values and will be ready to go to
309 void ocfs2_block_check_compute_bhs(struct buffer_head **bhs, int nr,
310 struct ocfs2_block_check *bc)
320 memset(bc, 0, sizeof(struct ocfs2_block_check));
322 for (i = 0, crc = ~0, ecc = 0; i < nr; i++) {
323 crc = crc32_le(crc, bhs[i]->b_data, bhs[i]->b_size);
325 * The number of bits in a buffer is obviously b_size*8.
326 * The offset of this buffer is b_size*i, so the bit offset
327 * of this buffer is b_size*8*i.
329 ecc = (u16)ocfs2_hamming_encode(ecc, bhs[i]->b_data,
331 bhs[i]->b_size * 8 * i);
335 * No ecc'd ocfs2 structure is larger than 4K, so ecc will be no
336 * larger than 16 bits.
338 BUG_ON(ecc > USHORT_MAX);
340 bc->bc_crc32e = cpu_to_le32(crc);
341 bc->bc_ecc = cpu_to_le16((u16)ecc);
345 * This function validates existing check information on a list of
346 * buffer_heads. Like _compute_bhs, the function will take care of
347 * zeroing bc before calculating check codes. If bc is not a pointer
348 * inside data, the caller must have zeroed any inline
349 * ocfs2_block_check structures.
351 * Again, the data passed in should be the on-disk endian.
353 int ocfs2_block_check_validate_bhs(struct buffer_head **bhs, int nr,
354 struct ocfs2_block_check *bc)
357 struct ocfs2_block_check check;
365 check.bc_crc32e = le32_to_cpu(bc->bc_crc32e);
366 check.bc_ecc = le16_to_cpu(bc->bc_ecc);
368 memset(bc, 0, sizeof(struct ocfs2_block_check));
370 /* Fast path - if the crc32 validates, we're good to go */
371 for (i = 0, crc = ~0; i < nr; i++)
372 crc = crc32_le(crc, bhs[i]->b_data, bhs[i]->b_size);
373 if (crc == check.bc_crc32e)
377 "CRC32 failed: stored: %u, computed %u. Applying ECC.\n",
378 (unsigned int)check.bc_crc32e, (unsigned int)crc);
380 /* Ok, try ECC fixups */
381 for (i = 0, ecc = 0; i < nr; i++) {
383 * The number of bits in a buffer is obviously b_size*8.
384 * The offset of this buffer is b_size*i, so the bit offset
385 * of this buffer is b_size*8*i.
387 ecc = (u16)ocfs2_hamming_encode(ecc, bhs[i]->b_data,
389 bhs[i]->b_size * 8 * i);
391 fix = ecc ^ check.bc_ecc;
392 for (i = 0; i < nr; i++) {
394 * Try the fix against each buffer. It will only affect
397 ocfs2_hamming_fix(bhs[i]->b_data, bhs[i]->b_size * 8,
398 bhs[i]->b_size * 8 * i, fix);
401 /* And check the crc32 again */
402 for (i = 0, crc = ~0; i < nr; i++)
403 crc = crc32_le(crc, bhs[i]->b_data, bhs[i]->b_size);
404 if (crc == check.bc_crc32e)
407 mlog(ML_ERROR, "Fixed CRC32 failed: stored: %u, computed %u\n",
408 (unsigned int)check.bc_crc32e, (unsigned int)crc);
413 bc->bc_crc32e = cpu_to_le32(check.bc_crc32e);
414 bc->bc_ecc = cpu_to_le16(check.bc_ecc);
420 * These are the main API. They check the superblock flag before
421 * calling the underlying operations.
423 * They expect the buffer(s) to be in disk format.
425 void ocfs2_compute_meta_ecc(struct super_block *sb, void *data,
426 struct ocfs2_block_check *bc)
428 if (ocfs2_meta_ecc(OCFS2_SB(sb)))
429 ocfs2_block_check_compute(data, sb->s_blocksize, bc);
432 int ocfs2_validate_meta_ecc(struct super_block *sb, void *data,
433 struct ocfs2_block_check *bc)
437 if (ocfs2_meta_ecc(OCFS2_SB(sb)))
438 rc = ocfs2_block_check_validate(data, sb->s_blocksize, bc);
443 void ocfs2_compute_meta_ecc_bhs(struct super_block *sb,
444 struct buffer_head **bhs, int nr,
445 struct ocfs2_block_check *bc)
447 if (ocfs2_meta_ecc(OCFS2_SB(sb)))
448 ocfs2_block_check_compute_bhs(bhs, nr, bc);
451 int ocfs2_validate_meta_ecc_bhs(struct super_block *sb,
452 struct buffer_head **bhs, int nr,
453 struct ocfs2_block_check *bc)
457 if (ocfs2_meta_ecc(OCFS2_SB(sb)))
458 rc = ocfs2_block_check_validate_bhs(bhs, nr, bc);