linux-kernel - Re: [PATCH] Force UNIX domain sockets to be built in

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Message-ID: <Pine.LNX.4.64.0712311628330.28123@fbirervta.pbzchgretzou.qr>
Date:	Mon, 31 Dec 2007 16:34:55 +0100 (CET)
From:	Jan Engelhardt <jengelh@...putergmbh.de>
To:	Bodo Eggert <7eggert@....de>
cc:	Adrian Bunk <bunk@...nel.org>, devzero@....de,
	linux-kernel@...r.kernel.org, netdev@...r.kernel.org
Subject: Re: [PATCH] Force UNIX domain sockets to be built in


On Dec 31 2007 16:19, Bodo Eggert wrote:
>Adrian Bunk wrote:
>> 
>> The only advantage I see is that the kernel image you have to flash 
>> can be made smaller - with the disadvantage that the running kernel
>> is bigger by more than 10%.
>> 
>> If you don't believe me, try it yourself:
>> Build all drivers statically into your kernel, and then compare the 
>> vmlinux sizes with CONFIG_MODULES=n and CONFIG_MODULES=y.
>
>If you'd aim for a small kernel image, you would build anything as a module 
>that is not requred for booting.
>
Yes, there is a tradeoff for both.

Example:
16:30 ichi:../net/802 > l fc.o fc.ko 
-rw-r--r-- 1 jengelh users 7961 Dec 27 15:19 fc.ko
-rw-r--r-- 1 jengelh users 2453 Dec 28 23:58 fc.o
(from a recent not-so-complete patch turning CONFIG_FC etc. into =m)

If fc was modular, it might save the 2453 bytes off the core kernel image,
but adds ~5508 bytes to disk.
So one has to pick =y or =m depending on whatever suits his/her situation.

But the choice should be _available_.

>>>> After all, changing it to a bool will allow us to make the
>>>> kernel image for nearly everyone smaller by a few hundred
>>>> bytes...
>>> 
>>> I can't see why optionally building it as a module would force us
>>> to make the kernel bigger. It may be a little more ugly to
>>> support =m, but thats it, isn't it?
>> 
>> On architectures like x86 where __exit code is freed at runtime 
>> af_unix_exit() makes your kernel image (but not the running kernel) 
>> bigger.
>> 
>> With CONFIG_MODULES=y the 13 EXPORT_SYMBOL's that only exist for
>> the theoretical possibility of CONIG_UNIX=m waste a few hundred
>> bytes of memory.
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