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

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Date:	Mon, 31 Dec 2007 16:42:55 +0200
From:	Adrian Bunk <bunk@...nel.org>
To:	Bodo Eggert <7eggert@....de>
Cc:	Jan Engelhardt <jengelh@...putergmbh.de>, devzero@....de,
	linux-kernel@...r.kernel.org, netdev@...r.kernel.org
Subject: Re: [PATCH] Force UNIX domain sockets to be built in

On Mon, Dec 31, 2007 at 02:26:42PM +0100, Bodo Eggert wrote:
> On Mon, 31 Dec 2007, Adrian Bunk wrote:
> > On Mon, Dec 31, 2007 at 01:09:43PM +0100, Bodo Eggert wrote:
> 
> > > As suggested by Adrian Bunk, UNIX domain sockets should always be built in 
> > > on normal systems. This is especially true since udev needs these sockets
> > > and fails to run if UNIX=m.
> > > 
> > > Signed-Off-By: Bodo Eggert <7eggert@....de>
> > > 
> > > ---
> > > Last minute change: I decided against making it a bool because embedded 
> > > folks might depend on a small kernel image. Edited in the patch below.
> > >...
> > 
> > Is this just a purely theoretical thought or is this a reasonable use 
> > case people actually use in practice?
>  
> For now, it's a theoretical thought, but having an embedded device, I can 
> see the reason for $EVERYTHING=m there.

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.

> > 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.

cu
Adrian

-- 

       "Is there not promise of rain?" Ling Tan asked suddenly out
        of the darkness. There had been need of rain for many days.
       "Only a promise," Lao Er said.
                                       Pearl S. Buck - Dragon Seed

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