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@xxxxxx>

---
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)".
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Relevant Pages

  • Re: [PATCH] Force UNIX domain sockets to be built in
    ... 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'd aim for a small kernel image, you would build anything as a module ...
    (Linux-Kernel)
  • Re: [PATCH] Force UNIX domain sockets to be built in
    ... and fails to run if UNIX=m. ... folks might depend on a small kernel image. ... For now, it's a theoretical thought, but having an embedded device, I can ... see the reason for $EVERYTHING=m there. ...
    (Linux-Kernel)