linux-kernel - Re: [PATCH v8 00/25] Re-use nvram module

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Date:   Sun, 30 Dec 2018 11:09:13 +1100 (AEDT)
From:   Finn Thain <fthain@...egraphics.com.au>
To:     Arnd Bergmann <arnd@...db.de>
cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-m68k <linux-m68k@...ts.linux-m68k.org>,
        linuxppc-dev <linuxppc-dev@...ts.ozlabs.org>
Subject: Re: [PATCH v8 00/25] Re-use nvram module

On Sat, 29 Dec 2018, Arnd Bergmann wrote:

> I had a look at the complete series now, and I think this is a great 
> cleanup. I replied with a couple of minor comments that you may or may 
> not want to address first.
> 

Thanks for reviewing this.

> The one thing I would like to see resolved (I hope this doesn't bring 
> back an old discussion you had already concluded) is regarding the use 
> of a global exported structure of function pointers, as opposed to using 
> either directly exported functions (with a consistent interface) or a 
> boot-time selectable structure like dma_map_ops or ppc_md.
> 

If I understand correctly, /dev/nvram was made obsolete by the nvmem 
subsystem (?). If so, there won't be new /dev/nvram users, and the 
refactoring here only has to be sufficiently flexible to meet the needs of 
existing users.

I'm not opposed to exported functions in place of a singleton ops struct. 
Other things being equal I'm inclined toward the ops struct, perhaps 
because I like encapsulation or perhaps because I don't like excess 
generality. (That design decision was made years ago and I don't remember 
the reasoning.)

All the arch_nvram_ops structs that I've defined in these patches have the 
'const' properly:

const struct nvram_ops arch_nvram_ops = {
       .read_byte      = nvram_read_byte,
       .write_byte     = nvram_write_byte,
       .read           = nvram_read,
       .write          = nvram_write,
       .get_size       = nvram_get_size,
       .set_checksum   = nvram_set_checksum,
       .initialize     = nvram_initialize,
};
EXPORT_SYMBOL(arch_nvram_ops);

This is because there's no need to do any run-time reconfiguration.

Is a collection of exported functions a better fit here?

-- 

>     Arnd
>