linux-kernel - Re: [PATCH v3 1/3] lib: add crc64 calculation routines

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Date:   Tue, 17 Jul 2018 18:43:05 +0300
From:   Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
To:     Coly Li <colyli@...e.de>, linux-kernel@...r.kernel.org
Cc:     linux-bcache@...r.kernel.org, linux-block@...r.kernel.org,
        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>,
        Eric Biggers <ebiggers3@...il.com>
Subject: Re: [PATCH v3 1/3] lib: add crc64 calculation routines

On Tue, 2018-07-17 at 22:55 +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
> 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 64bits-long
>   numbers, this talbe 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

Thanks for an update! My comments below.

> Co-developed-by: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>

As required by coding style this tag should be accompanied with SoB of
co-developer(s).

> +u64 __pure crc64_update(u64 crc, const void *_p, size_t len);

For sake of consistency I would name _len as well.

> + * Normal 64bit CRC calculation.

I think 64-bit form is slightly better and more often

$ git grep -n -w 64bit | wc -l
809

$ git grep -n -w 64-bit | wc -l
2957

> + * crc64table[256] is the lookup table of a table-driver 64bit CRC

Ditto.

> + * Copyright 2018 SUSE Linux.
> + *   Author: Coly Li <colyli@...e.de>

> + *

This (blank comment) line is not needed.

> +u64 __pure crc64_update(u64 crc, const void *_p, size_t len)

_len ?

> + * Copyright 2018 SUSE Linux.
> + *   Author: Coly Li <colyli@...e.de>

> + *

Not needed line.


> +#include <inttypes.h>
> +#include <stdio.h>

+ blank line? Would separate groups of headers logically.

> +#include <linux/swab.h>

> +static int64_t crc64_table[256] = {0,};

I guess {0} would work as well (no comma).

> +	printf("#include <uapi/linux/types.h>\n");
> +	printf("#include <linux/cache.h>\n\n");

Do wee need these? CRC32 case seems fine without.

-- 
Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Intel Finland Oy