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

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Message-ID: <cd71e845-2046-d723-2d57-09acd52f933d@suse.de>
Date:   Wed, 18 Jul 2018 21:58:59 +0800
From:   Coly Li <colyli@...e.de>
To:     Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Cc:     linux-kernel@...r.kernel.org, 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>,
        Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH v3 1/3] lib: add crc64 calculation routines

On 2018/7/17 11:43 PM, Andy Shevchenko wrote:
> 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).
> 

Now I change the lines as following in commit log,
Co-developed-by: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Signed-off-by: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>

>> +u64 __pure crc64_update(u64 crc, const void *_p, size_t len);
> 
> For sake of consistency I would name _len as well.
> 

Hmm, I will use 'p', and use '_p' for internal argument.

>> + * 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.
> 

Sure, I will change them to 64-bit.

>> + * 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 ?
> 

I will rename '_p' to 'p' here too.

>> + * Copyright 2018 SUSE Linux.
>> + *   Author: Coly Li <colyli@...e.de>
> 
>> + *
> 
> Not needed line.
> 

Fixed in v4.

>> +#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).

Fixed them in v4.

> 
>> +	printf("#include <uapi/linux/types.h>\n");
>> +	printf("#include <linux/cache.h>\n\n");
> 
> Do wee need these? CRC32 case seems fine without.
> 

I renamed uapi/linux/types.h to linux/types.h, this header is for 'u64'.
Another header linux/cache.h is for '____cacheline_aligned'. They should
be necessary if these two headers are not included before
lib/crc64table.h is included.

Thanks for your review :-)

Coly Li