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// SPDX-License-Identifier: GPL-2.0-only
/* -*- 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.
*/
#include <linux/kernel.h>
#include <linux/types.h>
#include <linux/crc32.h>
#include <linux/buffer_head.h>
#include <linux/bitops.h>
#include <linux/debugfs.h>
#include <linux/module.h>
#include <linux/fs.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 offset 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);
}
/*
* Debugfs handling.
*/
#ifdef CONFIG_DEBUG_FS
static int blockcheck_u64_get(void *data, u64 *val)
{
*val = *(u64 *)data;
return 0;
}
DEFINE_SIMPLE_ATTRIBUTE(blockcheck_fops, blockcheck_u64_get, NULL, "%llu\n");
static struct dentry *blockcheck_debugfs_create(const char *name,
struct dentry *parent,
u64 *value)
{
return debugfs_create_file(name, S_IFREG | S_IRUSR, parent, value,
&blockcheck_fops);
}
static void ocfs2_blockcheck_debug_remove(struct ocfs2_blockcheck_stats *stats)
{
if (stats) {
debugfs_remove(stats->b_debug_check);
stats->b_debug_check = NULL;
debugfs_remove(stats->b_debug_failure);
stats->b_debug_failure = NULL;
debugfs_remove(stats->b_debug_recover);
stats->b_debug_recover = NULL;
debugfs_remove(stats->b_debug_dir);
stats->b_debug_dir = NULL;
}
}
static int ocfs2_blockcheck_debug_install(struct ocfs2_blockcheck_stats *stats,
struct dentry *parent)
{
int rc = -EINVAL;
if (!stats)
goto out;
stats->b_debug_dir = debugfs_create_dir("blockcheck", parent);
if (!stats->b_debug_dir)
goto out;
stats->b_debug_check =
blockcheck_debugfs_create("blocks_checked",
stats->b_debug_dir,
&stats->b_check_count);
stats->b_debug_failure =
blockcheck_debugfs_create("checksums_failed",
stats->b_debug_dir,
&stats->b_failure_count);
stats->b_debug_recover =
blockcheck_debugfs_create("ecc_recoveries",
stats->b_debug_dir,
&stats->b_recover_count);
if (stats->b_debug_check && stats->b_debug_failure &&
stats->b_debug_recover)
rc = 0;
out:
if (rc)
ocfs2_blockcheck_debug_remove(stats);
return rc;
}
#else
static inline int ocfs2_blockcheck_debug_install(struct ocfs2_blockcheck_stats *stats,
struct dentry *parent)
{
return 0;
}
static inline void ocfs2_blockcheck_debug_remove(struct ocfs2_blockcheck_stats *stats)
{
}
#endif /* CONFIG_DEBUG_FS */
/* Always-called wrappers for starting and stopping the debugfs files */
int ocfs2_blockcheck_stats_debugfs_install(struct ocfs2_blockcheck_stats *stats,
struct dentry *parent)
{
return ocfs2_blockcheck_debug_install(stats, parent
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