Re: [PATCH 01/18] block/rnbd: fix mixed module-builtin object

From: Andrew Davis <afd@ti.com>
To: Masahiro Yamada <masahiroy@kernel.org>
Cc: Alexander Lobakin <alobakin@pm.me>,
	<linux-kbuild@vger.kernel.org>,
	Nicolas Schier <nicolas@fjasle.eu>, Jens Axboe <axboe@kernel.dk>,
	"Boris Brezillon" <bbrezillon@kernel.org>,
	Borislav Petkov <bp@alien8.de>, Tony Luck <tony.luck@intel.com>,
	Miquel Raynal <miquel.raynal@bootlin.com>,
	"Vladimir Oltean" <vladimir.oltean@nxp.com>,
	Alexandre Belloni <alexandre.belloni@bootlin.com>,
	Derek Chickles <dchickles@marvell.com>,
	Ioana Ciornei <ioana.ciornei@nxp.com>,
	Salil Mehta <salil.mehta@huawei.com>,
	Sunil Goutham <sgoutham@marvell.com>,
	Grygorii Strashko <grygorii.strashko@ti.com>,
	Daniel Scally <djrscally@gmail.com>,
	"Hans de Goede" <hdegoede@redhat.com>,
	Mark Brown <broonie@kernel.org>,
	Andy Shevchenko <andriy.shevchenko@linux.intel.com>,
	NXP Linux Team <linux-imx@nxp.com>, <netdev@vger.kernel.org>,
	<linux-kernel@vger.kernel.org>
Subject: Re: [PATCH 01/18] block/rnbd: fix mixed module-builtin object
Date: Tue, 29 Nov 2022 12:24:56 -0600	[thread overview]
Message-ID: <922413d0-c566-7765-f374-6f64d94f39aa@ti.com> (raw)
In-Reply-To: <CAK7LNAT_PuL0vuYaPxKZ3AfrojBC2tEXUA7Gqs2VuVuoTVoXmQ@mail.gmail.com>

On 11/21/22 11:59 PM, Masahiro Yamada wrote:
> On Tue, Nov 22, 2022 at 6:18 AM Andrew Davis <afd@ti.com> wrote:
>>
>> On 11/19/22 5:04 PM, Alexander Lobakin wrote:
>>> From: Masahiro Yamada <masahiroy@kernel.org>
>>>
>>> With CONFIG_BLK_DEV_RNBD_CLIENT=m and CONFIG_BLK_DEV_RNBD_SERVER=y
>>> (or vice versa), rnbd-common.o is linked to a module and also to
>>> vmlinux even though CFLAGS are different between builtins and modules.
>>>
>>> This is the same situation as fixed by commit 637a642f5ca5 ("zstd:
>>> Fixing mixed module-builtin objects").
>>>
>>> Turn rnbd_access_mode_str() into an inline function.
>>>
>>
>> Why inline? All you should need is "static" to keep these internal to
>> each compilation unit. Inline also bloats the object files when the
>> function is called from multiple places. Let the compiler decide when
>> to inline.
>>
>> Andrew
> 
> 
> Since it is a header file.
> 
> 
> In header files, "static inline" should be always used.
> Never "static".
> 

My comment was more "why"?

> 
> If a header is included from a C file and there is a function
> that is not used from that C file,
> "static" would emit -Wunused-function warning
> (-Wunused-function is enabled by -Wall, which is the case
> for the kernel build).
> 
> 

Inline still hints to the compiler to inline, causing unneeded
object size bloat. Using "inline" to signal something else (that
the function may be unused) when we already have a flag for that
(__maybe_unused) feels wrong.

Seems this was already debated way back in 2006.. So maybe not
worth revisiting today, but still a cleanup that could be good
to think more about later.

Andrew