```// SPDX-License-Identifier: GPL-2.0-only
/*
* blockcheck.c
*
* Checksum and ECC codes for the OCFS2 userspace library.
*
*/

#include <linux/kernel.h>
#include <linux/types.h>
#include <linux/crc32.h>
#include <linux/bitops.h>
#include <linux/debugfs.h>
#include <linux/module.h>
#include <linux/fs.h>
#include <asm/byteorder.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="https://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_DEBUGFS_ATTRIBUTE(blockcheck_fops, blockcheck_u64_get, NULL, "%llu\n");

static void ocfs2_blockcheck_debug_remove(struct ocfs2_blockcheck_stats *stats)
{
if (stats) {
debugfs_remove_recursive(stats->b_debug_dir);
stats->b_debug_dir = NULL;
}
}

static void ocfs2_blockcheck_debug_install(struct ocfs2_blockcheck_stats *stats,
struct dentry *parent)
{
struct dentry *dir;

dir = debugfs_create_dir("blockcheck", parent);
stats->b_debug_dir = dir;

debugfs_create_file("blocks_checked", S_IFREG | S_IRUSR, dir,
&stats->b_check_count, &blockcheck_fops);

debugfs_create_file("checksums_failed", S_IFREG | S_IRUSR, dir,
&stats->b_failure_count, &blockcheck_fops);

debugfs_create_file("ecc_recoveries", S_IFREG | S_IRUSR, dir,
&stats->b_recover_count, &blockcheck_fops);

}
#else
static inline void ocfs2_blockcheck_debug_install(struct ocfs2_blockcheck_stats *stats,
struct dentry *parent)
{
}

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 */
void ocfs2_blockcheck_stats_debugfs_install(struct ocfs2_blockcheck_stats *stats,
struct dentry *parent)
{
ocfs2_blockcheck_debug_install(stats, parent);
}

void ocfs2_blockcheck_stats_debugfs_remove(struct ocfs2_blockcheck_stats *stats)
{
ocfs2_blockcheck_debug_remove(stats);
}

static void ocfs2_blockcheck_inc_check(struct ocfs2_blockcheck_stats *stats)
{
u64 new_count;

if (!stats)
return;

spin_lock(&stats->b_lock);
stats->b_check_count++;
new_count = stats->b_check_count;
spin_unlock(&stats->b_lock);

if (!new_count)
mlog(ML_NOTICE, "Block check count has wrapped\n");
}

static void ocfs2_blockcheck_inc_failure(struct ocfs2_blockcheck_stats *stats)
{
u64 new_count;

if (!stats)
return;

spin_lock(&stats->b_lock);
stats->b_failure_count++;
new_count = stats->b_failure_count;
spin_unlock(&stats->b_lock);

if (!new_count)
mlog(ML_NOTICE, "Checksum failure count has wrapped\n");
}

static void ocfs2_blockcheck_inc_recover(struct ocfs2_blockcheck_stats *stats)
{
u64 new_count;

if (!stats)
return;

spin_lock(&stats->b_lock);
stats->b_recover_count++;
new_count = stats->b_recover_count;
spin_unlock(&stats->b_lock);

if (!new_count)
mlog(ML_NOTICE, "ECC recovery count has wrapped\n");
}

/*
* These are the low-level APIs for using the ocfs2_block_check structure.
*/

/*
* 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 > USHRT_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,
struct ocfs2_blockcheck_stats *stats)
{
int rc = 0;
u32 bc_crc32e;
u16 bc_ecc;
u32 crc, ecc;

ocfs2_blockcheck_inc_check(stats);

bc_crc32e = le32_to_cpu(bc->bc_crc32e);
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 == bc_crc32e)
goto out;

ocfs2_blockcheck_inc_failure(stats);
mlog(ML_ERROR,
"CRC32 failed: stored: 0x%x, computed 0x%x. Applying ECC.\n",
(unsigned int)bc_crc32e, (unsigned int)crc);

/* Ok, try ECC fixups */
ecc = ocfs2_hamming_encode_block(data, blocksize);
ocfs2_hamming_fix_block(data, blocksize, ecc ^ bc_ecc);

/* And check the crc32 again */
crc = crc32_le(~0, data, blocksize);
if (crc == bc_crc32e) {
ocfs2_blockcheck_inc_recover(stats);
goto out;
}

mlog(ML_ERROR, "Fixed CRC32 failed: stored: 0x%x, computed 0x%x\n",
(unsigned int)bc_crc32e, (unsigned int)crc);

rc = -EIO;

out:
bc->bc_crc32e = cpu_to_le32(bc_crc32e);
bc->bc_ecc = cpu_to_le16(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(ecc > USHRT_MAX);

bc->bc_crc32e = cpu_to_le32(crc);
bc->bc_ecc = cpu_to_le16((u16)ecc);
}

/*
* This function validates existing check information on a list of
* buffer_heads.  Like _compute_bhs, 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_bhs(struct buffer_head **bhs, int nr,
struct ocfs2_block_check *bc,
struct ocfs2_blockcheck_stats *stats)
{
int i, rc = 0;
u32 bc_crc32e;
u16 bc_ecc;
u32 crc, ecc, fix;

BUG_ON(nr < 0);

if (!nr)
return 0;

ocfs2_blockcheck_inc_check(stats);

bc_crc32e = le32_to_cpu(bc->bc_crc32e);
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 */
for (i = 0, crc = ~0; i < nr; i++)
crc = crc32_le(crc, bhs[i]->b_data, bhs[i]->b_size);
if (crc == bc_crc32e)
goto out;

ocfs2_blockcheck_inc_failure(stats);
mlog(ML_ERROR,
"CRC32 failed: stored: %u, computed %u.  Applying ECC.\n",
(unsigned int)bc_crc32e, (unsigned int)crc);

/* Ok, try ECC fixups */
for (i = 0, ecc = 0; i < nr; i++) {
/*
* 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);
}
fix = ecc ^ bc_ecc;
for (i = 0; i < nr; i++) {
/*
* Try the fix against each buffer.  It will only affect
* one of them.
*/
ocfs2_hamming_fix(bhs[i]->b_data, bhs[i]->b_size * 8,
bhs[i]->b_size * 8 * i, fix);
}

/* And check the crc32 again */
for (i = 0, crc = ~0; i < nr; i++)
crc = crc32_le(crc, bhs[i]->b_data, bhs[i]->b_size);
if (crc == bc_crc32e) {
ocfs2_blockcheck_inc_recover(stats);
goto out;
}

mlog(ML_ERROR, "Fixed CRC32 failed: stored: %u, computed %u\n",
(unsigned int)bc_crc32e, (unsigned int)crc);

rc = -EIO;

out:
bc->bc_crc32e = cpu_to_le32(bc_crc32e);
bc->bc_ecc = cpu_to_le16(bc_ecc);

return rc;
}

/*
* These are the main API.  They check the superblock flag before
* calling the underlying operations.
*
* They expect the buffer(s) to be in disk format.
*/
void ocfs2_compute_meta_ecc(struct super_block *sb, void *data,
struct ocfs2_block_check *bc)
{
if (ocfs2_meta_ecc(OCFS2_SB(sb)))
ocfs2_block_check_compute(data, sb->s_blocksize, bc);
}

int ocfs2_validate_meta_ecc(struct super_block *sb, void *data,
struct ocfs2_block_check *bc)
{
int rc = 0;
struct ocfs2_super *osb = OCFS2_SB(sb);

if (ocfs2_meta_ecc(osb))
rc = ocfs2_block_check_validate(data, sb->s_blocksize, bc,
&osb->osb_ecc_stats);

return rc;
}

void ocfs2_compute_meta_ecc_bhs(struct super_block *sb,
struct ocfs2_block_check *bc)
{
if (ocfs2_meta_ecc(OCFS2_SB(sb)))
ocfs2_block_check_compute_bhs(bhs, nr, bc);
}

int ocfs2_validate_meta_ecc_bhs(struct super_block *sb,