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

From: Coly Li
Date: Wed Jul 18 2018 - 09:59:19 EST


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@xxxxxxxxxxxxxxx>
>
> 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@xxxxxxxxxxxxxxx>
Signed-off-by: Andy Shevchenko <andriy.shevchenko@xxxxxxxxxxxxxxx>

>> +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@xxxxxxx>
>
>> + *
>
> 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@xxxxxxx>
>
>> + *
>
> 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