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feba04fd2c
Patch series "add crc64 calculation as kernel library", v5. This patchset adds basic implementation of crc64 calculation as a Linux kernel library. Since bcache already does crc64 by itself, this patchset also modifies bcache code to use the new crc64 library routine. Currently bcache is the only user of crc64 calculation, another potential user is bcachefs which is on the way to be in mainline kernel. Therefore it makes sense to make crc64 calculation to be a public library. bcache uses crc64 as storage checksum, if a change of crc lib routines results an inconsistent result, the unmatched checksum may make bcache 'think' the on-disk is corrupted, such a change should be avoided or detected as early as possible. Therefore a patch is being prepared which adds a crc test framework, to check consistency of different calculations. This patch (of 2): Add the re-write crc64 calculation routines for Linux kernel. The CRC64 polynomical arithmetic follows ECMA-182 specification, inspired by CRC paper of Dr. Ross N. Williams (see http://www.ross.net/crc/download/crc_v3.txt) and other public domain implementations. All the changes work in this way, - When Linux kernel is built, host program lib/gen_crc64table.c will be compiled to lib/gen_crc64table and executed. - The output of gen_crc64table execution is an array called as lookup table (a.k.a POLY 0x42f0e1eba9ea369) which contain 256 64-bit long numbers, this table is dumped into header file lib/crc64table.h. - Then the header file is included by lib/crc64.c for normal 64bit crc calculation. - Function declaration of the crc64 calculation routines is placed in include/linux/crc64.h Currently bcache is the only user of crc64_be(), another potential user is bcachefs which is on the way to be in mainline kernel. Therefore it makes sense to move crc64 calculation into lib/crc64.c as public code. [colyli@suse.de: fix review comments from v4] Link: http://lkml.kernel.org/r/20180726053352.2781-2-colyli@suse.de Link: http://lkml.kernel.org/r/20180718165545.1622-2-colyli@suse.de Signed-off-by: Coly Li <colyli@suse.de> Co-developed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com> Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com> Reviewed-by: Hannes Reinecke <hare@suse.de> Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org> Cc: Andy Shevchenko <andriy.shevchenko@linux.intel.com> Cc: Michael Lyle <mlyle@lyle.org> Cc: Kent Overstreet <kent.overstreet@gmail.com> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Kate Stewart <kstewart@linuxfoundation.org> Cc: Eric Biggers <ebiggers3@gmail.com> Cc: Randy Dunlap <rdunlap@infradead.org> Cc: Noah Massey <noah.massey@gmail.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
57 lines
1.7 KiB
C
57 lines
1.7 KiB
C
// SPDX-License-Identifier: GPL-2.0
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/*
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* Normal 64-bit CRC calculation.
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*
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* This is a basic crc64 implementation following ECMA-182 specification,
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* which can be found from,
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* http://www.ecma-international.org/publications/standards/Ecma-182.htm
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*
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* Dr. Ross N. Williams has a great document to introduce the idea of CRC
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* algorithm, here the CRC64 code is also inspired by the table-driven
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* algorithm and detail example from this paper. This paper can be found
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* from,
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* http://www.ross.net/crc/download/crc_v3.txt
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*
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* crc64table[256] is the lookup table of a table-driven 64-bit CRC
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* calculation, which is generated by gen_crc64table.c in kernel build
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* time. The polynomial of crc64 arithmetic is from ECMA-182 specification
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* as well, which is defined as,
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*
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* x^64 + x^62 + x^57 + x^55 + x^54 + x^53 + x^52 + x^47 + x^46 + x^45 +
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* x^40 + x^39 + x^38 + x^37 + x^35 + x^33 + x^32 + x^31 + x^29 + x^27 +
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* x^24 + x^23 + x^22 + x^21 + x^19 + x^17 + x^13 + x^12 + x^10 + x^9 +
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* x^7 + x^4 + x + 1
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*
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* Copyright 2018 SUSE Linux.
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* Author: Coly Li <colyli@suse.de>
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*/
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#include <linux/module.h>
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#include <linux/types.h>
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#include "crc64table.h"
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MODULE_DESCRIPTION("CRC64 calculations");
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MODULE_LICENSE("GPL v2");
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/**
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* crc64_be - Calculate bitwise big-endian ECMA-182 CRC64
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* @crc: seed value for computation. 0 or (u64)~0 for a new CRC calculation,
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or the previous crc64 value if computing incrementally.
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* @p: pointer to buffer over which CRC64 is run
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* @len: length of buffer @p
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*/
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u64 __pure crc64_be(u64 crc, const void *p, size_t len)
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{
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size_t i, t;
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const unsigned char *_p = p;
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for (i = 0; i < len; i++) {
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t = ((crc >> 56) ^ (*_p++)) & 0xFF;
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crc = crc64table[t] ^ (crc << 8);
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}
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return crc;
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}
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EXPORT_SYMBOL_GPL(crc64_be);
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