58896c4d0e
The previous optimization used a fast find-highest-bit-set operation to give us a good starting point in calc_code_bit(). This version lets the caller cache the previous code buffer bit offset. Thus, the next call always starts where the last one left off. This reduces the calculation another 39%, for a total 80% reduction from the original, naive implementation. At least, on my machine. This also brings the parity calculation to within an order of magnitude of the crc32 calculation. Signed-off-by: Joel Becker <joel.becker@oracle.com> Signed-off-by: Mark Fasheh <mfasheh@suse.com>
478 lines
13 KiB
C
478 lines
13 KiB
C
/* -*- mode: c; c-basic-offset: 8; -*-
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* vim: noexpandtab sw=8 ts=8 sts=0:
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*
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* blockcheck.c
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*
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* Checksum and ECC codes for the OCFS2 userspace library.
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*
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* Copyright (C) 2006, 2008 Oracle. All rights reserved.
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*
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* This program is free software; you can redistribute it and/or
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* modify it under the terms of the GNU General Public
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* License, version 2, as published by the Free Software Foundation.
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*
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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* General Public License for more details.
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*/
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#include <linux/kernel.h>
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#include <linux/types.h>
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#include <linux/crc32.h>
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#include <linux/buffer_head.h>
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#include <linux/bitops.h>
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#include <asm/byteorder.h>
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#include <cluster/masklog.h>
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#include "ocfs2.h"
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#include "blockcheck.h"
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/*
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* We use the following conventions:
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*
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* d = # data bits
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* p = # parity bits
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* c = # total code bits (d + p)
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*/
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/*
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* Calculate the bit offset in the hamming code buffer based on the bit's
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* offset in the data buffer. Since the hamming code reserves all
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* power-of-two bits for parity, the data bit number and the code bit
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* number are offest by all the parity bits beforehand.
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*
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* Recall that bit numbers in hamming code are 1-based. This function
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* takes the 0-based data bit from the caller.
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*
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* An example. Take bit 1 of the data buffer. 1 is a power of two (2^0),
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* so it's a parity bit. 2 is a power of two (2^1), so it's a parity bit.
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* 3 is not a power of two. So bit 1 of the data buffer ends up as bit 3
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* in the code buffer.
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*
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* The caller can pass in *p if it wants to keep track of the most recent
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* number of parity bits added. This allows the function to start the
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* calculation at the last place.
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*/
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static unsigned int calc_code_bit(unsigned int i, unsigned int *p_cache)
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{
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unsigned int b, p = 0;
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/*
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* Data bits are 0-based, but we're talking code bits, which
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* are 1-based.
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*/
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b = i + 1;
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/* Use the cache if it is there */
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if (p_cache)
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p = *p_cache;
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b += p;
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/*
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* For every power of two below our bit number, bump our bit.
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*
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* We compare with (b + 1) because we have to compare with what b
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* would be _if_ it were bumped up by the parity bit. Capice?
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*
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* p is set above.
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*/
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for (; (1 << p) < (b + 1); p++)
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b++;
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if (p_cache)
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*p_cache = p;
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return b;
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}
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/*
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* This is the low level encoder function. It can be called across
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* multiple hunks just like the crc32 code. 'd' is the number of bits
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* _in_this_hunk_. nr is the bit offset of this hunk. So, if you had
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* two 512B buffers, you would do it like so:
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*
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* parity = ocfs2_hamming_encode(0, buf1, 512 * 8, 0);
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* parity = ocfs2_hamming_encode(parity, buf2, 512 * 8, 512 * 8);
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*
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* If you just have one buffer, use ocfs2_hamming_encode_block().
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*/
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u32 ocfs2_hamming_encode(u32 parity, void *data, unsigned int d, unsigned int nr)
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{
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unsigned int i, b, p = 0;
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BUG_ON(!d);
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/*
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* b is the hamming code bit number. Hamming code specifies a
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* 1-based array, but C uses 0-based. So 'i' is for C, and 'b' is
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* for the algorithm.
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*
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* The i++ in the for loop is so that the start offset passed
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* to ocfs2_find_next_bit_set() is one greater than the previously
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* found bit.
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*/
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for (i = 0; (i = ocfs2_find_next_bit(data, d, i)) < d; i++)
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{
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/*
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* i is the offset in this hunk, nr + i is the total bit
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* offset.
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*/
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b = calc_code_bit(nr + i, &p);
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/*
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* Data bits in the resultant code are checked by
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* parity bits that are part of the bit number
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* representation. Huh?
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*
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* <wikipedia href="http://en.wikipedia.org/wiki/Hamming_code">
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* In other words, the parity bit at position 2^k
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* checks bits in positions having bit k set in
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* their binary representation. Conversely, for
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* instance, bit 13, i.e. 1101(2), is checked by
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* bits 1000(2) = 8, 0100(2)=4 and 0001(2) = 1.
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* </wikipedia>
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*
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* Note that 'k' is the _code_ bit number. 'b' in
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* our loop.
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*/
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parity ^= b;
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}
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/* While the data buffer was treated as little endian, the
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* return value is in host endian. */
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return parity;
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}
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u32 ocfs2_hamming_encode_block(void *data, unsigned int blocksize)
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{
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return ocfs2_hamming_encode(0, data, blocksize * 8, 0);
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}
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/*
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* Like ocfs2_hamming_encode(), this can handle hunks. nr is the bit
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* offset of the current hunk. If bit to be fixed is not part of the
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* current hunk, this does nothing.
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*
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* If you only have one hunk, use ocfs2_hamming_fix_block().
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*/
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void ocfs2_hamming_fix(void *data, unsigned int d, unsigned int nr,
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unsigned int fix)
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{
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unsigned int i, b;
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BUG_ON(!d);
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/*
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* If the bit to fix has an hweight of 1, it's a parity bit. One
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* busted parity bit is its own error. Nothing to do here.
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*/
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if (hweight32(fix) == 1)
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return;
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/*
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* nr + d is the bit right past the data hunk we're looking at.
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* If fix after that, nothing to do
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*/
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if (fix >= calc_code_bit(nr + d, NULL))
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return;
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/*
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* nr is the offset in the data hunk we're starting at. Let's
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* start b at the offset in the code buffer. See hamming_encode()
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* for a more detailed description of 'b'.
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*/
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b = calc_code_bit(nr, NULL);
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/* If the fix is before this hunk, nothing to do */
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if (fix < b)
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return;
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for (i = 0; i < d; i++, b++)
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{
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/* Skip past parity bits */
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while (hweight32(b) == 1)
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b++;
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/*
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* i is the offset in this data hunk.
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* nr + i is the offset in the total data buffer.
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* b is the offset in the total code buffer.
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*
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* Thus, when b == fix, bit i in the current hunk needs
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* fixing.
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*/
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if (b == fix)
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{
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if (ocfs2_test_bit(i, data))
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ocfs2_clear_bit(i, data);
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else
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ocfs2_set_bit(i, data);
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break;
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}
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}
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}
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void ocfs2_hamming_fix_block(void *data, unsigned int blocksize,
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unsigned int fix)
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{
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ocfs2_hamming_fix(data, blocksize * 8, 0, fix);
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}
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/*
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* This function generates check information for a block.
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* data is the block to be checked. bc is a pointer to the
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* ocfs2_block_check structure describing the crc32 and the ecc.
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*
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* bc should be a pointer inside data, as the function will
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* take care of zeroing it before calculating the check information. If
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* bc does not point inside data, the caller must make sure any inline
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* ocfs2_block_check structures are zeroed.
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*
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* The data buffer must be in on-disk endian (little endian for ocfs2).
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* bc will be filled with little-endian values and will be ready to go to
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* disk.
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*/
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void ocfs2_block_check_compute(void *data, size_t blocksize,
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struct ocfs2_block_check *bc)
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{
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u32 crc;
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u32 ecc;
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memset(bc, 0, sizeof(struct ocfs2_block_check));
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crc = crc32_le(~0, data, blocksize);
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ecc = ocfs2_hamming_encode_block(data, blocksize);
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/*
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* No ecc'd ocfs2 structure is larger than 4K, so ecc will be no
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* larger than 16 bits.
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*/
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BUG_ON(ecc > USHORT_MAX);
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bc->bc_crc32e = cpu_to_le32(crc);
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bc->bc_ecc = cpu_to_le16((u16)ecc);
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}
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/*
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* This function validates existing check information. Like _compute,
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* the function will take care of zeroing bc before calculating check codes.
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* If bc is not a pointer inside data, the caller must have zeroed any
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* inline ocfs2_block_check structures.
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*
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* Again, the data passed in should be the on-disk endian.
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*/
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int ocfs2_block_check_validate(void *data, size_t blocksize,
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struct ocfs2_block_check *bc)
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{
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int rc = 0;
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struct ocfs2_block_check check;
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u32 crc, ecc;
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check.bc_crc32e = le32_to_cpu(bc->bc_crc32e);
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check.bc_ecc = le16_to_cpu(bc->bc_ecc);
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memset(bc, 0, sizeof(struct ocfs2_block_check));
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/* Fast path - if the crc32 validates, we're good to go */
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crc = crc32_le(~0, data, blocksize);
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if (crc == check.bc_crc32e)
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goto out;
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mlog(ML_ERROR,
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"CRC32 failed: stored: %u, computed %u. Applying ECC.\n",
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(unsigned int)check.bc_crc32e, (unsigned int)crc);
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/* Ok, try ECC fixups */
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ecc = ocfs2_hamming_encode_block(data, blocksize);
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ocfs2_hamming_fix_block(data, blocksize, ecc ^ check.bc_ecc);
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/* And check the crc32 again */
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crc = crc32_le(~0, data, blocksize);
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if (crc == check.bc_crc32e)
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goto out;
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mlog(ML_ERROR, "Fixed CRC32 failed: stored: %u, computed %u\n",
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(unsigned int)check.bc_crc32e, (unsigned int)crc);
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rc = -EIO;
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out:
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bc->bc_crc32e = cpu_to_le32(check.bc_crc32e);
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bc->bc_ecc = cpu_to_le16(check.bc_ecc);
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return rc;
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}
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/*
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* This function generates check information for a list of buffer_heads.
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* bhs is the blocks to be checked. bc is a pointer to the
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* ocfs2_block_check structure describing the crc32 and the ecc.
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*
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* bc should be a pointer inside data, as the function will
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* take care of zeroing it before calculating the check information. If
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* bc does not point inside data, the caller must make sure any inline
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* ocfs2_block_check structures are zeroed.
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*
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* The data buffer must be in on-disk endian (little endian for ocfs2).
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* bc will be filled with little-endian values and will be ready to go to
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* disk.
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*/
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void ocfs2_block_check_compute_bhs(struct buffer_head **bhs, int nr,
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struct ocfs2_block_check *bc)
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{
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int i;
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u32 crc, ecc;
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BUG_ON(nr < 0);
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if (!nr)
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return;
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memset(bc, 0, sizeof(struct ocfs2_block_check));
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for (i = 0, crc = ~0, ecc = 0; i < nr; i++) {
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crc = crc32_le(crc, bhs[i]->b_data, bhs[i]->b_size);
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/*
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* The number of bits in a buffer is obviously b_size*8.
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* The offset of this buffer is b_size*i, so the bit offset
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* of this buffer is b_size*8*i.
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*/
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ecc = (u16)ocfs2_hamming_encode(ecc, bhs[i]->b_data,
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bhs[i]->b_size * 8,
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bhs[i]->b_size * 8 * i);
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}
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/*
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* No ecc'd ocfs2 structure is larger than 4K, so ecc will be no
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* larger than 16 bits.
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*/
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BUG_ON(ecc > USHORT_MAX);
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bc->bc_crc32e = cpu_to_le32(crc);
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bc->bc_ecc = cpu_to_le16((u16)ecc);
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}
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/*
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* This function validates existing check information on a list of
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* buffer_heads. Like _compute_bhs, the function will take care of
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* zeroing bc before calculating check codes. If bc is not a pointer
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* inside data, the caller must have zeroed any inline
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* ocfs2_block_check structures.
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*
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* Again, the data passed in should be the on-disk endian.
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*/
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int ocfs2_block_check_validate_bhs(struct buffer_head **bhs, int nr,
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struct ocfs2_block_check *bc)
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{
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int i, rc = 0;
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struct ocfs2_block_check check;
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u32 crc, ecc, fix;
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BUG_ON(nr < 0);
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if (!nr)
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return 0;
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check.bc_crc32e = le32_to_cpu(bc->bc_crc32e);
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check.bc_ecc = le16_to_cpu(bc->bc_ecc);
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memset(bc, 0, sizeof(struct ocfs2_block_check));
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/* Fast path - if the crc32 validates, we're good to go */
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for (i = 0, crc = ~0; i < nr; i++)
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crc = crc32_le(crc, bhs[i]->b_data, bhs[i]->b_size);
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if (crc == check.bc_crc32e)
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goto out;
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mlog(ML_ERROR,
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"CRC32 failed: stored: %u, computed %u. Applying ECC.\n",
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(unsigned int)check.bc_crc32e, (unsigned int)crc);
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/* Ok, try ECC fixups */
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for (i = 0, ecc = 0; i < nr; i++) {
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/*
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* The number of bits in a buffer is obviously b_size*8.
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* The offset of this buffer is b_size*i, so the bit offset
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* of this buffer is b_size*8*i.
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*/
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ecc = (u16)ocfs2_hamming_encode(ecc, bhs[i]->b_data,
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bhs[i]->b_size * 8,
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bhs[i]->b_size * 8 * i);
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}
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fix = ecc ^ check.bc_ecc;
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for (i = 0; i < nr; i++) {
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/*
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* Try the fix against each buffer. It will only affect
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* one of them.
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*/
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ocfs2_hamming_fix(bhs[i]->b_data, bhs[i]->b_size * 8,
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bhs[i]->b_size * 8 * i, fix);
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}
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/* And check the crc32 again */
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for (i = 0, crc = ~0; i < nr; i++)
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crc = crc32_le(crc, bhs[i]->b_data, bhs[i]->b_size);
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if (crc == check.bc_crc32e)
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goto out;
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mlog(ML_ERROR, "Fixed CRC32 failed: stored: %u, computed %u\n",
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(unsigned int)check.bc_crc32e, (unsigned int)crc);
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rc = -EIO;
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out:
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bc->bc_crc32e = cpu_to_le32(check.bc_crc32e);
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bc->bc_ecc = cpu_to_le16(check.bc_ecc);
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return rc;
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}
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/*
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* These are the main API. They check the superblock flag before
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* calling the underlying operations.
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*
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* They expect the buffer(s) to be in disk format.
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*/
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void ocfs2_compute_meta_ecc(struct super_block *sb, void *data,
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struct ocfs2_block_check *bc)
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{
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if (ocfs2_meta_ecc(OCFS2_SB(sb)))
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ocfs2_block_check_compute(data, sb->s_blocksize, bc);
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}
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int ocfs2_validate_meta_ecc(struct super_block *sb, void *data,
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struct ocfs2_block_check *bc)
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{
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int rc = 0;
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if (ocfs2_meta_ecc(OCFS2_SB(sb)))
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rc = ocfs2_block_check_validate(data, sb->s_blocksize, bc);
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return rc;
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}
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void ocfs2_compute_meta_ecc_bhs(struct super_block *sb,
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struct buffer_head **bhs, int nr,
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struct ocfs2_block_check *bc)
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{
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if (ocfs2_meta_ecc(OCFS2_SB(sb)))
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ocfs2_block_check_compute_bhs(bhs, nr, bc);
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}
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int ocfs2_validate_meta_ecc_bhs(struct super_block *sb,
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struct buffer_head **bhs, int nr,
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struct ocfs2_block_check *bc)
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{
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int rc = 0;
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if (ocfs2_meta_ecc(OCFS2_SB(sb)))
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rc = ocfs2_block_check_validate_bhs(bhs, nr, bc);
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return rc;
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}
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