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

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Message-ID: <alpine.LSU.0.999.0712311553530.4211@be1.lrz>
Date:	Mon, 31 Dec 2007 16:19:23 +0100 (CET)
From:	Bodo Eggert <7eggert@....de>
To:	Adrian Bunk <bunk@...nel.org>
cc:	Bodo Eggert <7eggert@....de>,
	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, 31 Dec 2007, Adrian Bunk wrote:
> 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.

If you'd aim for a small kernel image, you would build anything as a module 
that is not requred for booting.

> > > 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.

#define m='m'
#if CONIG_UNIX=='m'
#define EXPORT_SYMBOL_AF_UNIX EXPORT_SYMBOL
#else
#define EXPORT_SYMBOL_AF_UNIX()
#endif
#undef m

You could also use "#if defined(C_U) && (C_U == m)".
-- 
Funny quotes:
36. You never really learn to swear until you learn to drive.
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