Commit 70ad1ba7 authored by Joel Becker's avatar Joel Becker Committed by Mark Fasheh
Browse files

ocfs2: Add the underlying blockcheck code. 



This is the code that computes crc32 and ecc for ocfs2 metadata blocks.
There are high-level functions that check whether the filesystem has the
ecc feature, mid-level functions that work on a single block or array of
buffer_heads, and the low-level ecc hamming code that can handle
multiple buffers like crc32_le().

It's not hooked up to the filesystem yet.

Signed-off-by: default avatarJoel Becker <joel.becker@oracle.com>
Cc: Christoph Hellwig <hch@lst.de>
Signed-off-by: default avatarMark Fasheh <mfasheh@suse.com>
parent ab552d54

fs/ocfs2/Makefile

+1 −0
Original line number Diff line number Diff line
@@ -12,6 +12,7 @@ obj-$(CONFIG_OCFS2_FS_USERSPACE_CLUSTER) += ocfs2_stack_user.o 
ocfs2-objs := \

	alloc.o 		\

	aops.o 			\

	blockcheck.o		\

	buffer_head_io.o	\

	dcache.o 		\

	dir.o 			\

fs/ocfs2/blockcheck.c

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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 "ocfs2.h"



#include "blockcheck.h"







/*

 * We use the following conventions:

 *

 * d = # data bits

 * p = # parity bits

 * c = # total code bits (d + p)

 */

static int calc_parity_bits(unsigned int d)

{

	unsigned int p;



	/*

	 * Bits required for Single Error Correction is as follows:

	 *

	 * d + p + 1 <= 2^p

	 *

	 * We're restricting ourselves to 31 bits of parity, that should be

	 * sufficient.

	 */

	for (p = 1; p < 32; p++)

	{

		if ((d + p + 1) <= (1 << p))

			return p;

	}



	return 0;

}



/*

 * 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.

 */

static unsigned int calc_code_bit(unsigned int i)

{

	unsigned int b, p;



	/*

	 * Data bits are 0-based, but we're talking code bits, which

	 * are 1-based.

	 */

	b = i + 1;



	/*

	 * For every power of two below our bit number, bump our bit.

	 *

	 * We compare with (b + 1) becuase we have to compare with what b

	 * would be _if_ it were bumped up by the parity bit.  Capice?

	 */

	for (p = 0; (1 << p) < (b + 1); p++)

		b++;



	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 p = calc_parity_bits(nr + d);

	unsigned int i, j, b;



	BUG_ON(!p);



	/*

	 * 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);



		for (j = 0; j < p; j++)

		{

			/*

			 * 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.

			 */

			if (b & (1 << j))

				parity ^= (1 << j);

		}

	}



	/* 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 p = calc_parity_bits(nr + d);

	unsigned int i, b;



	BUG_ON(!p);



	/*

	 * 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))

		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);

	/* 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;



	/* 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;



	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(ecc > USHORT_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)

{

	int i, rc = 0;

	struct ocfs2_block_check check;

	u32 crc, ecc, fix;



	BUG_ON(nr < 0);



	if (!nr)

		return 0;



	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 */

	for (i = 0, crc = ~0; i < nr; i++)

		crc = crc32_le(crc, bhs[i]->b_data, bhs[i]->b_size);

	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 */

	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 ^ check.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 == 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;

}



/*

 * 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;



	if (ocfs2_meta_ecc(OCFS2_SB(sb)))

		rc = ocfs2_block_check_validate(data, sb->s_blocksize, bc);



	return rc;

}



void ocfs2_compute_meta_ecc_bhs(struct super_block *sb,

				struct buffer_head **bhs, int nr,

				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,

				struct buffer_head **bhs, int nr,

				struct ocfs2_block_check *bc)

{

	int rc = 0;



	if (ocfs2_meta_ecc(OCFS2_SB(sb)))

		rc = ocfs2_block_check_validate_bhs(bhs, nr, bc);



	return rc;

}

fs/ocfs2/blockcheck.h

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Original line number Diff line number Diff line 
/* -*- mode: c; c-basic-offset: 8; -*-

 * vim: noexpandtab sw=8 ts=8 sts=0:

 *

 * blockcheck.h

 *

 * Checksum and ECC codes for the OCFS2 userspace library.

 *

 * Copyright (C) 2004, 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.

 */



#ifndef OCFS2_BLOCKCHECK_H

#define OCFS2_BLOCKCHECK_H





/* High level block API */

void ocfs2_compute_meta_ecc(struct super_block *sb, void *data,

			    struct ocfs2_block_check *bc);

int ocfs2_validate_meta_ecc(struct super_block *sb, void *data,

			    struct ocfs2_block_check *bc);

void ocfs2_compute_meta_ecc_bhs(struct super_block *sb,

				struct buffer_head **bhs, int nr,

				struct ocfs2_block_check *bc);

int ocfs2_validate_meta_ecc_bhs(struct super_block *sb,

				struct buffer_head **bhs, int nr,

				struct ocfs2_block_check *bc);



/* Lower level API */

void ocfs2_block_check_compute(void *data, size_t blocksize,

			       struct ocfs2_block_check *bc);

int ocfs2_block_check_validate(void *data, size_t blocksize,

			       struct ocfs2_block_check *bc);

void ocfs2_block_check_compute_bhs(struct buffer_head **bhs, int nr,

				   struct ocfs2_block_check *bc);

int ocfs2_block_check_validate_bhs(struct buffer_head **bhs, int nr,

				   struct ocfs2_block_check *bc);



/*

 * Hamming code functions

 */



/*

 * Encoding hamming code parity bits for a buffer.

 *

 * 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);

/*

 * Fix a buffer with a bit error.  The 'fix' is the original parity

 * xor'd with the parity calculated now.

 *

 * 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 buffer, use ocfs2_hamming_fix_block().

 */

void ocfs2_hamming_fix(void *data, unsigned int d, unsigned int nr,

		       unsigned int fix);



/* Convenience wrappers for a single buffer of data */

extern u32 ocfs2_hamming_encode_block(void *data, unsigned int blocksize);

extern void ocfs2_hamming_fix_block(void *data, unsigned int blocksize,

				    unsigned int fix);

#endif

fs/ocfs2/ocfs2.h

+8 −0
Original line number Diff line number Diff line
@@ -382,6 +382,13 @@ static inline int ocfs2_supports_xattr(struct ocfs2_super *osb) 
	return 0;

}



static inline int ocfs2_meta_ecc(struct ocfs2_super *osb)

{

	if (osb->s_feature_incompat & OCFS2_FEATURE_INCOMPAT_META_ECC)

		return 1;

	return 0;

}



/* set / clear functions because cluster events can make these happen

 * in parallel so we want the transitions to be atomic. this also

 * means that any future flags osb_flags must be protected by spinlock
@@ -615,5 +622,6 @@ static inline s16 ocfs2_get_inode_steal_slot(struct ocfs2_super *osb) 
#define ocfs2_clear_bit ext2_clear_bit

#define ocfs2_test_bit ext2_test_bit

#define ocfs2_find_next_zero_bit ext2_find_next_zero_bit

#define ocfs2_find_next_bit ext2_find_next_bit

#endif  /* OCFS2_H */

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