linux-kernel - Re: [PATCH v4 1/3] lib: add crc64 calculation routines

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Date:   Wed, 25 Jul 2018 00:29:24 +0800
From:   Coly Li <colyli@...e.de>
To:     Eric Biggers <ebiggers3@...il.com>
Cc:     linux-kernel@...r.kernel.org, linux-bcache@...r.kernel.org,
        linux-block@...r.kernel.org,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Michael Lyle <mlyle@...e.org>,
        Kent Overstreet <kent.overstreet@...il.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Kate Stewart <kstewart@...uxfoundation.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Randy Dunlap <rdunlap@...radead.org>
Subject: Re: [PATCH v4 1/3] lib: add crc64 calculation routines

On 2018/7/24 12:26 PM, Eric Biggers wrote:
> On Thu, Jul 19, 2018 at 12:55:43AM +0800, Coly Li wrote:
>> This patch adds the re-write crc64 calculation routines for Linux kernel.
>> The CRC64 polynomical arithmetic follows ECMA-182 specification, inspired
> 
> "polynomical" => "polynomial".  Same everywhere else in the patches.
> 

Hi Eric,

Thanks for your careful review. I will post a fixing patch to fix all
these issues.

Coly Li

>> + * crc64table[256] is the lookup table of a table-driver 64-bit CRC
> 
> "table-driver" => "table-driven"
> 
>> + * calculation, which is generated by gen_crc64table.c in kernel build
>> + * time. The polynomial of crc64 arithmetic is from ECMA-182 specification
>> + * as well, which is defined as,
>> + *
>> + * x^64 + x^62 + x^57 + x^55 + x^54 + x^53 + x^52 + x^47 + x^46 + x^45 +
>> + * x^40 + x^39 + x^38 + x^37 + x^35 + x^33 + x^32 + x^31 + x^29 + x^27 +
>> + * x^24 + x^23 + x^22 + x^21 + x^19 + x^17 + x^13 + x^12 + x^10 + x^9 +
>> + * x^7 + x^4 + x + 1
>> + *
>> + * Copyright 2018 SUSE Linux.
>> + *   Author: Coly Li <colyli@...e.de>
>> + */
>> +
>> +#include <linux/module.h>
>> +#include <linux/types.h>
>> +#include "crc64table.h"
>> +
>> +MODULE_DESCRIPTION("CRC64 calculations");
>> +MODULE_LICENSE("GPL v2");
>> +
>> +/**
>> + * crc64_be - Calculate bitwise big-endian ECMA-182 CRC64
>> + * @crc: seed value for computation. 0 for a new CRC computing, or the
>> + *	previous crc64 value if computing incrementally.
> 
> "0 or (u64)~0 for a new CRC calculation".  Both conventions are common in CRCs.
> In fact the all-ones convention is generally considered better, because it
> causes leading zeroes in the data to affect the checksum.
> 
>> + * @p: pointer to buffer over which CRC64 is run
>> + * @len: length of buffer @p
>> + */
>> +u64 __pure crc64_be(u64 crc, const void *p, size_t len)
>> +{
>> +	size_t i, t;
>> +
>> +	const unsigned char *_p = p;
>> +
>> +	for (i = 0; i < len; i++) {
>> +		t = ((crc >> 56) ^ (*_p++)) & 0xFF;
>> +		crc = crc64table[t] ^ (crc << 8);
>> +	}
>> +
>> +	return crc;
>> +}
>> +EXPORT_SYMBOL_GPL(crc64_be);
>> diff --git a/lib/gen_crc64table.c b/lib/gen_crc64table.c
>> new file mode 100644
>> index 000000000000..8296b0c3ea30
>> --- /dev/null
>> +++ b/lib/gen_crc64table.c
>> @@ -0,0 +1,68 @@
>> +// SPDX-License-Identifier: GPL-2.0
>> +/*
>> + * Generate lookup table for the talbe-driven CRC64 calculation.
> 
> "talbe-driven" => "table-driven"
> 
>> + *
>> + * gen_crc64table is executed in kernel build time and generates
>> + * lib/crc64table.h. This header is included by lib/crc64.c for
>> + * the table-driver CRC64 calculation.
> 
> "table-driver" => "table-driven"
> 
>> + *
>> + * See lib/crc64.c for more information about which specification
>> + * and polynomical arithmetic that gen_crc64table.c follows to
>> + * generate the lookup table.
>> + *
>> + * Copyright 2018 SUSE Linux.
>> + *   Author: Coly Li <colyli@...e.de>
>> + */
>> +#include <inttypes.h>
>> +#include <stdio.h>
>> +
>> +#include <linux/swab.h>
>> +
>> +#define CRC64_ECMA182_POLY 0x42F0E1EBA9EA3693ULL
>> +
>> +static int64_t crc64_table[256] = {0};
> 
> This really should be uint64_t, not int64_t.
> 
>> +
>> +static void generate_crc64_table(void)
>> +{
>> +	uint64_t i, j, c, crc;
>> +
>> +	for (i = 0; i < 256; i++) {
>> +		crc = 0;
>> +		c = i << 56;
>> +
>> +		for (j = 0; j < 8; j++) {
>> +			if ((crc ^ c) & 0x8000000000000000ULL)
>> +				crc = (crc << 1) ^ CRC64_ECMA182_POLY;
>> +			else
>> +				crc <<= 1;
>> +			c <<= 1;
>> +		}
>> +
>> +		crc64_table[i] = crc;
>> +	}
>> +}
>> +
>> +static void print_crc64_table(void)
>> +{
>> +	int i;
>> +
>> +	printf("/* this file is generated - do not edit */\n\n");
>> +	printf("#include <linux/types.h>\n");
>> +	printf("#include <linux/cache.h>\n\n");
>> +	printf("static const u64 ____cacheline_aligned crc64table[256] = {\n");
>> +	for (i = 0; i < 256; i++) {
>> +		printf("\t0x%016" PRIx64 "ULL", crc64_table[i]);
>> +		if (i & 0x1)
>> +			printf(",\n");
>> +		else
>> +			printf(", ");
>> +	}
>> +	printf("};\n");
>> +}
>> +
>> +int main(int argc, char *argv[])
>> +{
>> +	generate_crc64_table();
>> +	print_crc64_table();
>> +	return 0;
>> +}
>> -- 
>> 2.17.1
>>
> 
> - Eric
>