linux-kernel - Re: Object code duplication in sound/pci/echoaudio/

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Date:	Thu, 14 May 2015 22:32:06 +0200
From:	Giuliano Pochini <pochini@...ny.it>
To:	Denys Vlasenko <dvlasenk@...hat.com>
Cc:	Takashi Iwai <tiwai@...e.de>, Jaroslav Kysela <perex@...e.cz>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: Object code duplication in sound/pci/echoaudio/

On Mon, 11 May 2015 22:15:28 +0200
Denys Vlasenko <dvlasenk@...hat.com> wrote:

> There are fourteen files in sound/pci/echoaudio/, namely:
> 
> darla20.c darla24.c echo3g.c gina20.c gina24.c indigo.c
> indigodj.c indigodjx.c indigoio.c indigoiox.c layla20.c
> layla24.c mia.c mona.c
> 
> Which use the following method of "code reuse":
> 
> #include "echoaudio_dsp.c"
> #include "echoaudio_gml.c"
> #include "echoaudio.c"
> 
> echoaudio.c is not a header file, it contains a bunch of
> static functions, some of a considerable size.
> This makes those functions to be duplicated many times over.

Not really. It is quite unlikely that there are two different Echoaudio cards installed.


> For instance, there are fourteen instances of init_engine(),
> each 1117 bytes long. Fourteen instances of pcm_open(), each 556 bytes
> long.
> 
> 11 get_firmware
> 10 free_firmware
> 13 audiopipe_free
> 14 init_hw
> 14 hw_rule_capture_format_by_channels
> 14 hw_rule_capture_channels_by_format
> 14 hw_rule_playback_format_by_channels
> 14 hw_rule_playback_channels_by_format
> 
> and so on.
> 
> In my humble opinion, this is not a good coding practice.
> You should not duplicate functions like this.
> Where possible, you need to reuse a single instance of a function.

One option is to make a single driver which supports all the cards. There is not any duplicated code, but there is a lot of unused code. The other way (the one I choosed) is to build many specialized drivers. There is duplicated code overall, but given a single installed card there is neither duplicated not unused code.


-- 
Giuliano.
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