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|
/* -*- 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)
*/
/*
* 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.
*
* The caller can pass in *p if it wants to keep track of the most recent
* number of parity bits added. This allows the function to start the
* calculation at the last place.
*/
static unsigned int calc_code_bit(unsigned int i, unsigned int *p_cache)
{
unsigned int b, p = 0;
/*
* Data bits are 0-based, but we're talking code bits, which
* are 1-based.
*/
b = i + 1;
/* Use the cache if it is there */
if (p_cache)
p = *p_cache;
b += p;
/*
* For every power of two below our bit number, bump our bit.
*
* We compare with (b + 1) because we have to compare with what b
* would be _if_ it were bumped up by the parity bit. Capice?
*
* p is set above.
*/
for (; (1 << p) < (b + 1); p++)
b++;
if (p_cache)
*p_cache = p;
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 i, b, p = 0;
BUG_ON(!d);
/*
* 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, &p);
/*
* 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.
*/
parity ^= b;
}
/* 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 i, b;
BUG_ON(!d);
/*
* 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, NULL))
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, NULL);
/* 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
|