linux-kernel - Re: [RFC 1/2] CRC32 Add GenWQE CRC to kernel CRC code

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Date:	Wed, 18 Dec 2013 16:55:58 -0800
From:	Greg KH <gregkh@...uxfoundation.org>
To:	Frank Haverkamp <haver@...ux.vnet.ibm.com>
Cc:	linux-kernel@...r.kernel.org, arnd@...db.de,
	cody@...ux.vnet.ibm.com, schwidefsky@...ibm.com,
	utz.bacher@...ibm.com, mmarek@...e.cz, rmallon@...il.com,
	jsvogt@...ibm.com, MIJUNG@...ibm.com, cascardo@...ux.vnet.ibm.com,
	michael@...ra.de
Subject: Re: [RFC 1/2] CRC32 Add GenWQE CRC to kernel CRC code

On Wed, Dec 11, 2013 at 05:49:22PM +0100, Frank Haverkamp wrote:
> Our GenWQE driver is using a CRC32 polynom, which as far as I could
> see, no one else is using in the kernel. In its original version we
> implemented our own CRC32, but I think it is nicer to use the common
> code as suggested by Greg.
> 
> I did not want to add yet another crc32g_table and waste (1KiB) memory
> when no one else is using it. I tried to externalize the
> crc32init_be_generic and crc32_be_generic functions. I failed. The
> crc32init* I found is used to autogenerate code can is itself not part
> of the resulting kernel.
> 
> As result I gave up on that approach and just added the GenWQE special
> polynom in addition to the other 3 crc tables. I wanted to figure out
> if it is possible in principle to use the generic code.
> 
> Is the consumption of 1KiB for a little table justifyable if it 
> currently has just one user?
> 
> Signed-off-by: Frank Haverkamp <haver@...ux.vnet.ibm.com>
> ---
>  include/linux/crc32.h |    2 	2 +	0 -	0 !
>  lib/crc32.c           |   10 	10 +	0 -	0 !
>  lib/crc32defs.h       |    5 	5 +	0 -	0 !
>  lib/gen_crc32table.c  |   39 	31 +	8 -	0 !
>  4 files changed, 48 insertions(+), 8 deletions(-)

What kind of crazy diffstat is that?  What generated it?

> 
> --- a/include/linux/crc32.h
> +++ b/include/linux/crc32.h
> @@ -11,6 +11,8 @@
>  extern u32  crc32_le(u32 crc, unsigned char const *p, size_t len);
>  extern u32  crc32_be(u32 crc, unsigned char const *p, size_t len);
>  
> +extern u32  __crc32g_be(u32 crc, unsigned char const *p, size_t len);

Ick, don't export __ functions, that means something is not quite right
with the api, don't you agree?

Why not just export crc32g_be() and make the changes inside the crc32.c
file to handle that?

thanks,

greg k-h
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