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1 | /* -*- mode: c; c-basic-offset: 8; -*- |
2 | * vim: noexpandtab sw=8 ts=8 sts=0: | |
3 | * | |
4 | * blockcheck.c | |
5 | * | |
6 | * Checksum and ECC codes for the OCFS2 userspace library. | |
7 | * | |
8 | * Copyright (C) 2006, 2008 Oracle. All rights reserved. | |
9 | * | |
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. | |
13 | * | |
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. | |
18 | */ | |
19 | ||
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> | |
26 | ||
27 | #include "ocfs2.h" | |
28 | ||
29 | #include "blockcheck.h" | |
30 | ||
31 | ||
32 | ||
33 | /* | |
34 | * We use the following conventions: | |
35 | * | |
36 | * d = # data bits | |
37 | * p = # parity bits | |
38 | * c = # total code bits (d + p) | |
39 | */ | |
40 | static int calc_parity_bits(unsigned int d) | |
41 | { | |
42 | unsigned int p; | |
43 | ||
44 | /* | |
45 | * Bits required for Single Error Correction is as follows: | |
46 | * | |
47 | * d + p + 1 <= 2^p | |
48 | * | |
49 | * We're restricting ourselves to 31 bits of parity, that should be | |
50 | * sufficient. | |
51 | */ | |
52 | for (p = 1; p < 32; p++) | |
53 | { | |
54 | if ((d + p + 1) <= (1 << p)) | |
55 | return p; | |
56 | } | |
57 | ||
58 | return 0; | |
59 | } | |
60 | ||
61 | /* | |
62 | * Calculate the bit offset in the hamming code buffer based on the bit's | |
63 | * offset in the data buffer. Since the hamming code reserves all | |
64 | * power-of-two bits for parity, the data bit number and the code bit | |
65 | * number are offest by all the parity bits beforehand. | |
66 | * | |
67 | * Recall that bit numbers in hamming code are 1-based. This function | |
68 | * takes the 0-based data bit from the caller. | |
69 | * | |
70 | * An example. Take bit 1 of the data buffer. 1 is a power of two (2^0), | |
71 | * so it's a parity bit. 2 is a power of two (2^1), so it's a parity bit. | |
72 | * 3 is not a power of two. So bit 1 of the data buffer ends up as bit 3 | |
73 | * in the code buffer. | |
74 | */ | |
75 | static unsigned int calc_code_bit(unsigned int i) | |
76 | { | |
77 | unsigned int b, p; | |
78 | ||
79 | /* | |
80 | * Data bits are 0-based, but we're talking code bits, which | |
81 | * are 1-based. | |
82 | */ | |
83 | b = i + 1; | |
84 | ||
85 | /* | |
86 | * For every power of two below our bit number, bump our bit. | |
87 | * | |
88 | * We compare with (b + 1) becuase we have to compare with what b | |
89 | * would be _if_ it were bumped up by the parity bit. Capice? | |
90 | */ | |
91 | for (p = 0; (1 << p) < (b + 1); p++) | |
92 | b++; | |
93 | ||
94 | return b; | |
95 | } | |
96 | ||
97 | /* | |
98 | * This is the low level encoder function. It can be called across | |
99 | * multiple hunks just like the crc32 code. 'd' is the number of bits | |
100 | * _in_this_hunk_. nr is the bit offset of this hunk. So, if you had | |
101 | * two 512B buffers, you would do it like so: | |
102 | * | |
103 | * parity = ocfs2_hamming_encode(0, buf1, 512 * 8, 0); | |
104 | * parity = ocfs2_hamming_encode(parity, buf2, 512 * 8, 512 * 8); | |
105 | * | |
106 | * If you just have one buffer, use ocfs2_hamming_encode_block(). | |
107 | */ | |
108 | u32 ocfs2_hamming_encode(u32 parity, void *data, unsigned int d, unsigned int nr) | |
109 | { | |
110 | unsigned int p = calc_parity_bits(nr + d); | |
111 | unsigned int i, j, b; | |
112 | ||
113 | BUG_ON(!p); | |
114 | ||
115 | /* | |
116 | * b is the hamming code bit number. Hamming code specifies a | |
117 | * 1-based array, but C uses 0-based. So 'i' is for C, and 'b' is | |
118 | * for the algorithm. | |
119 | * | |
120 | * The i++ in the for loop is so that the start offset passed | |
121 | * to ocfs2_find_next_bit_set() is one greater than the previously | |
122 | * found bit. | |
123 | */ | |
124 | for (i = 0; (i = ocfs2_find_next_bit(data, d, i)) < d; i++) | |
125 | { | |
126 | /* | |
127 | * i is the offset in this hunk, nr + i is the total bit | |
128 | * offset. | |
129 | */ | |
130 | b = calc_code_bit(nr + i); | |
131 | ||
132 | for (j = 0; j < p; j++) | |
133 | { | |
134 | /* | |
135 | * Data bits in the resultant code are checked by | |
136 | * parity bits that are part of the bit number | |
137 | * representation. Huh? | |
138 | * | |
139 | * <wikipedia href="http://en.wikipedia.org/wiki/Hamming_code"> | |
140 | * In other words, the parity bit at position 2^k | |
141 | * checks bits in positions having bit k set in | |
142 | * their binary representation. Conversely, for | |
143 | * instance, bit 13, i.e. 1101(2), is checked by | |
144 | * bits 1000(2) = 8, 0100(2)=4 and 0001(2) = 1. | |
145 | * </wikipedia> | |
146 | * | |
147 | * Note that 'k' is the _code_ bit number. 'b' in | |
148 | * our loop. | |
149 | */ | |
150 | if (b & (1 << j)) | |
151 | parity ^= (1 << j); | |
152 | } | |
153 | } | |
154 | ||
155 | /* While the data buffer was treated as little endian, the | |
156 | * return value is in host endian. */ | |
157 | return parity; | |
158 | } | |
159 | ||
160 | u32 ocfs2_hamming_encode_block(void *data, unsigned int blocksize) | |
161 | { | |
162 | return ocfs2_hamming_encode(0, data, blocksize * 8, 0); | |
163 | } | |
164 | ||
165 | /* | |
166 | * Like ocfs2_hamming_encode(), this can handle hunks. nr is the bit | |
167 | * offset of the current hunk. If bit to be fixed is not part of the | |
168 | * current hunk, this does nothing. | |
169 | * | |
170 | * If you only have one hunk, use ocfs2_hamming_fix_block(). | |
171 | */ | |
172 | void ocfs2_hamming_fix(void *data, unsigned int d, unsigned int nr, | |
173 | unsigned int fix) | |
174 | { | |
175 | unsigned int p = calc_parity_bits(nr + d); | |
176 | unsigned int i, b; | |
177 | ||
178 | BUG_ON(!p); | |
179 | ||
180 | /* | |
181 | * If the bit to fix has an hweight of 1, it's a parity bit. One | |
182 | * busted parity bit is its own error. Nothing to do here. | |
183 | */ | |
184 | if (hweight32(fix) == 1) | |
185 | return; | |
186 | ||
187 | /* | |
188 | * nr + d is the bit right past the data hunk we're looking at. | |
189 | * If fix after that, nothing to do | |
190 | */ | |
191 | if (fix >= calc_code_bit(nr + d)) | |
192 | return; | |
193 | ||
194 | /* | |
195 | * nr is the offset in the data hunk we're starting at. Let's | |
196 | * start b at the offset in the code buffer. See hamming_encode() | |
197 | * for a more detailed description of 'b'. | |
198 | */ | |
199 | b = calc_code_bit(nr); | |
200 | /* If the fix is before this hunk, nothing to do */ | |
201 | if (fix < b) | |
202 | return; | |
203 | ||
204 | for (i = 0; i < d; i++, b++) | |
205 | { | |
206 | /* Skip past parity bits */ | |
207 | while (hweight32(b) == 1) | |
208 | b++; | |
209 | ||
210 | /* | |
211 | * i is the offset in this data hunk. | |
212 | * nr + i is the offset in the total data buffer. | |
213 | * b is the offset in the total code buffer. | |
214 | * | |
215 | * Thus, when b == fix, bit i in the current hunk needs | |
216 | * fixing. | |
217 | */ | |
218 | if (b == fix) | |
219 | { | |
220 | if (ocfs2_test_bit(i, data)) | |
221 | ocfs2_clear_bit(i, data); | |
222 | else | |
223 | ocfs2_set_bit(i, data); | |
224 | break; | |
225 | } | |
226 | } | |
227 | } | |
228 | ||
229 | void ocfs2_hamming_fix_block(void *data, unsigned int blocksize, | |
230 | unsigned int fix) | |
231 | { | |
232 | ocfs2_hamming_fix(data, blocksize * 8, 0, fix); | |
233 | } | |
234 | ||
235 | /* | |
236 | * This function generates check information for a block. | |
237 | * data is the block to be checked. bc is a pointer to the | |
238 | * ocfs2_block_check structure describing the crc32 and the ecc. | |
239 | * | |
240 | * bc should be a pointer inside data, as the function will | |
241 | * take care of zeroing it before calculating the check information. If | |
242 | * bc does not point inside data, the caller must make sure any inline | |
243 | * ocfs2_block_check structures are zeroed. | |
244 | * | |
245 | * The data buffer must be in on-disk endian (little endian for ocfs2). | |
246 | * bc will be filled with little-endian values and will be ready to go to | |
247 | * disk. | |
248 | */ | |
249 | void ocfs2_block_check_compute(void *data, size_t blocksize, | |
250 | struct ocfs2_block_check *bc) | |
251 | { | |
252 | u32 crc; | |
253 | u32 ecc; | |
254 | ||
255 | memset(bc, 0, sizeof(struct ocfs2_block_check)); | |
256 | ||
257 | crc = crc32_le(~0, data, blocksize); | |
258 | ecc = ocfs2_hamming_encode_block(data, blocksize); | |
259 | ||
260 | /* | |
261 | * No ecc'd ocfs2 structure is larger than 4K, so ecc will be no | |
262 | * larger than 16 bits. | |
263 | */ | |
264 | BUG_ON(ecc > USHORT_MAX); | |
265 | ||
266 | bc->bc_crc32e = cpu_to_le32(crc); | |
267 | bc->bc_ecc = cpu_to_le16((u16)ecc); | |
268 | } | |
269 | ||
270 | /* | |
271 | * This function validates existing check information. Like _compute, | |
272 | * the function will take care of zeroing bc before calculating check codes. | |
273 | * If bc is not a pointer inside data, the caller must have zeroed any | |
274 | * inline ocfs2_block_check structures. | |
275 | * | |
276 | * Again, the data passed in should be the on-disk endian. | |
277 | */ | |
278 | int ocfs2_block_check_validate(void *data, size_t blocksize, | |
279 | struct ocfs2_block_check *bc) | |
280 | { | |
281 | int rc = 0; | |
282 | struct ocfs2_block_check check; | |
283 | u32 crc, ecc; | |
284 | ||
285 | check.bc_crc32e = le32_to_cpu(bc->bc_crc32e); | |
286 | check.bc_ecc = le16_to_cpu(bc->bc_ecc); | |
287 | ||
288 | memset(bc, 0, sizeof(struct ocfs2_block_check)); | |
289 | ||
290 | /* Fast path - if the crc32 validates, we're good to go */ | |
291 | crc = crc32_le(~0, data, blocksize); | |
292 | if (crc == check.bc_crc32e) | |
293 | goto out; | |
294 | ||
295 | /* Ok, try ECC fixups */ | |
296 | ecc = ocfs2_hamming_encode_block(data, blocksize); | |
297 | ocfs2_hamming_fix_block(data, blocksize, ecc ^ check.bc_ecc); | |
298 | ||
299 | /* And check the crc32 again */ | |
300 | crc = crc32_le(~0, data, blocksize); | |
301 | if (crc == check.bc_crc32e) | |
302 | goto out; | |
303 | ||
304 | rc = -EIO; | |
305 | ||
306 | out: | |
307 | bc->bc_crc32e = cpu_to_le32(check.bc_crc32e); | |
308 | bc->bc_ecc = cpu_to_le16(check.bc_ecc); | |
309 | ||
310 | return rc; | |
311 | } | |
312 | ||
313 | /* | |
314 | * This function generates check information for a list of buffer_heads. | |
315 | * bhs is the blocks to be checked. bc is a pointer to the | |
316 | * ocfs2_block_check structure describing the crc32 and the ecc. | |
317 | * | |
318 | * bc should be a pointer inside data, as the function will | |
319 | * take care of zeroing it before calculating the check information. If | |
320 | * bc does not point inside data, the caller must make sure any inline | |
321 | * ocfs2_block_check structures are zeroed. | |
322 | * | |
323 | * The data buffer must be in on-disk endian (little endian for ocfs2). | |
324 | * bc will be filled with little-endian values and will be ready to go to | |
325 | * disk. | |
326 | */ | |
327 | void ocfs2_block_check_compute_bhs(struct buffer_head **bhs, int nr, | |
328 | struct ocfs2_block_check *bc) | |
329 | { | |
330 | int i; | |
331 | u32 crc, ecc; | |
332 | ||
333 | BUG_ON(nr < 0); | |
334 | ||
335 | if (!nr) | |
336 | return; | |
337 | ||
338 | memset(bc, 0, sizeof(struct ocfs2_block_check)); | |
339 | ||
340 | for (i = 0, crc = ~0, ecc = 0; i < nr; i++) { | |
341 | crc = crc32_le(crc, bhs[i]->b_data, bhs[i]->b_size); | |
342 | /* | |
343 | * The number of bits in a buffer is obviously b_size*8. | |
344 | * The offset of this buffer is b_size*i, so the bit offset | |
345 | * of this buffer is b_size*8*i. | |
346 | */ | |
347 | ecc = (u16)ocfs2_hamming_encode(ecc, bhs[i]->b_data, | |
348 | bhs[i]->b_size * 8, | |
349 | bhs[i]->b_size * 8 * i); | |
350 | } | |
351 | ||
352 | /* | |
353 | * No ecc'd ocfs2 structure is larger than 4K, so ecc will be no | |
354 | * larger than 16 bits. | |
355 | */ | |
356 | BUG_ON(ecc > USHORT_MAX); | |
357 | ||
358 | bc->bc_crc32e = cpu_to_le32(crc); | |
359 | bc->bc_ecc = cpu_to_le16((u16)ecc); | |
360 | } | |
361 | ||
362 | /* | |
363 | * This function validates existing check information on a list of | |
364 | * buffer_heads. Like _compute_bhs, the function will take care of | |
365 | * zeroing bc before calculating check codes. If bc is not a pointer | |
366 | * inside data, the caller must have zeroed any inline | |
367 | * ocfs2_block_check structures. | |
368 | * | |
369 | * Again, the data passed in should be the on-disk endian. | |
370 | */ | |
371 | int ocfs2_block_check_validate_bhs(struct buffer_head **bhs, int nr, | |
372 | struct ocfs2_block_check *bc) | |
373 | { | |
374 | int i, rc = 0; | |
375 | struct ocfs2_block_check check; | |
376 | u32 crc, ecc, fix; | |
377 | ||
378 | BUG_ON(nr < 0); | |
379 | ||
380 | if (!nr) | |
381 | return 0; | |
382 | ||
383 | check.bc_crc32e = le32_to_cpu(bc->bc_crc32e); | |
384 | check.bc_ecc = le16_to_cpu(bc->bc_ecc); | |
385 | ||
386 | memset(bc, 0, sizeof(struct ocfs2_block_check)); | |
387 | ||
388 | /* Fast path - if the crc32 validates, we're good to go */ | |
389 | for (i = 0, crc = ~0; i < nr; i++) | |
390 | crc = crc32_le(crc, bhs[i]->b_data, bhs[i]->b_size); | |
391 | if (crc == check.bc_crc32e) | |
392 | goto out; | |
393 | ||
394 | mlog(ML_ERROR, | |
395 | "CRC32 failed: stored: %u, computed %u. Applying ECC.\n", | |
396 | (unsigned int)check.bc_crc32e, (unsigned int)crc); | |
397 | ||
398 | /* Ok, try ECC fixups */ | |
399 | for (i = 0, ecc = 0; i < nr; i++) { | |
400 | /* | |
401 | * The number of bits in a buffer is obviously b_size*8. | |
402 | * The offset of this buffer is b_size*i, so the bit offset | |
403 | * of this buffer is b_size*8*i. | |
404 | */ | |
405 | ecc = (u16)ocfs2_hamming_encode(ecc, bhs[i]->b_data, | |
406 | bhs[i]->b_size * 8, | |
407 | bhs[i]->b_size * 8 * i); | |
408 | } | |
409 | fix = ecc ^ check.bc_ecc; | |
410 | for (i = 0; i < nr; i++) { | |
411 | /* | |
412 | * Try the fix against each buffer. It will only affect | |
413 | * one of them. | |
414 | */ | |
415 | ocfs2_hamming_fix(bhs[i]->b_data, bhs[i]->b_size * 8, | |
416 | bhs[i]->b_size * 8 * i, fix); | |
417 | } | |
418 | ||
419 | /* And check the crc32 again */ | |
420 | for (i = 0, crc = ~0; i < nr; i++) | |
421 | crc = crc32_le(crc, bhs[i]->b_data, bhs[i]->b_size); | |
422 | if (crc == check.bc_crc32e) | |
423 | goto out; | |
424 | ||
425 | mlog(ML_ERROR, "Fixed CRC32 failed: stored: %u, computed %u\n", | |
426 | (unsigned int)check.bc_crc32e, (unsigned int)crc); | |
427 | ||
428 | rc = -EIO; | |
429 | ||
430 | out: | |
431 | bc->bc_crc32e = cpu_to_le32(check.bc_crc32e); | |
432 | bc->bc_ecc = cpu_to_le16(check.bc_ecc); | |
433 | ||
434 | return rc; | |
435 | } | |
436 | ||
437 | /* | |
438 | * These are the main API. They check the superblock flag before | |
439 | * calling the underlying operations. | |
440 | * | |
441 | * They expect the buffer(s) to be in disk format. | |
442 | */ | |
443 | void ocfs2_compute_meta_ecc(struct super_block *sb, void *data, | |
444 | struct ocfs2_block_check *bc) | |
445 | { | |
446 | if (ocfs2_meta_ecc(OCFS2_SB(sb))) | |
447 | ocfs2_block_check_compute(data, sb->s_blocksize, bc); | |
448 | } | |
449 | ||
450 | int ocfs2_validate_meta_ecc(struct super_block *sb, void *data, | |
451 | struct ocfs2_block_check *bc) | |
452 | { | |
453 | int rc = 0; | |
454 | ||
455 | if (ocfs2_meta_ecc(OCFS2_SB(sb))) | |
456 | rc = ocfs2_block_check_validate(data, sb->s_blocksize, bc); | |
457 | ||
458 | return rc; | |
459 | } | |
460 | ||
461 | void ocfs2_compute_meta_ecc_bhs(struct super_block *sb, | |
462 | struct buffer_head **bhs, int nr, | |
463 | struct ocfs2_block_check *bc) | |
464 | { | |
465 | if (ocfs2_meta_ecc(OCFS2_SB(sb))) | |
466 | ocfs2_block_check_compute_bhs(bhs, nr, bc); | |
467 | } | |
468 | ||
469 | int ocfs2_validate_meta_ecc_bhs(struct super_block *sb, | |
470 | struct buffer_head **bhs, int nr, | |
471 | struct ocfs2_block_check *bc) | |
472 | { | |
473 | int rc = 0; | |
474 | ||
475 | if (ocfs2_meta_ecc(OCFS2_SB(sb))) | |
476 | rc = ocfs2_block_check_validate_bhs(bhs, nr, bc); | |
477 | ||
478 | return rc; | |
479 | } | |
480 |