/* -*- 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 <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
  ");
  
  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);
  }
  
  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
  ");
  }
  
  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
  ");
  }
  
  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
  ");
  }
  
  
  
  /*
   * 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.
  ",

  	     (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
  ",

  	     (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.
  ",

  	     (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
  ",

  	     (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 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;

  	struct ocfs2_super *osb = OCFS2_SB(sb);

  	if (ocfs2_meta_ecc(osb))
  		rc = ocfs2_block_check_validate_bhs(bhs, nr, bc,
  						    &osb->osb_ecc_stats);

  
  	return rc;
  }