[Click] Minimizing patch size

[Joonwoo Park]

Hi Philip,

(2) The reason of patching "::" to ": :" is because "::" is namespace
keyword of c++ as you know.
It must be true that we can leave "::" in .c file as we builds .c with
c compiler not c++, however if "::" is in .h, since that .h will
possibly be included from .cpp file click linuxmodule, we need to
patch "::" to ": :" by all means.
Therefore I made a simple script to change every "::" to ": :" and
generated patch when I made patch for 2.6.24.7, I think you can revert
"::" changes in .c files if you'd like to do.
(3) compat shim would seem to me for finding out correct symbol table,
but since click uses c++ compiler .h has be modified to make c++
compiler happy,  I think we still need to provide c++ compile-able .h
files.  ie) structure member initializer, c++ keyword and etc... which
cannot be solved by 'extern "C"' keyword.

(1) At any rate, for recent version of linux, I believe right
direction is improving patchless to support newer version without
patching linux.

Joonwoo

On Mon, Jan 3, 2011 at 11:54 PM, Philip Prindeville
<philipp_subx at redfish-solutions.com> wrote:
> I was looking at the click kernel patches and noticed two things.
>
> (1) none of the kernels seem to be particularly recent.
> (2) a lot of the patches seem to be something other than added functionality.
>
> Looking, for instance, at:
>
> diff --git a/arch/arm/mach-iop13xx/irq.c b/arch/arm/mach-iop13xx/irq.c
> index 69f07b2..e217167 100644
> --- a/arch/arm/mach-iop13xx/irq.c
> +++ b/arch/arm/mach-iop13xx/irq.c
> @@ -38,7 +38,7 @@ static u32 read_intctl_0(void)
>  }
>  static void write_intctl_0(u32 val)
>  {
> -       asm volatile("mcr p6, 0, %0, c0, c4, 0"::"r" (val));
> +       asm volatile("mcr p6, 0, %0, c0, c4, 0": :"r" (val));
>  }
>
> ...
>
>
> I'm wondering why this is required? First, why would the C++ compiler try to compile a .c file, and second, why would it not be able to parse an asm() directive correctly?
>
> Looking over the patches, the "essential" ones are less than a thousand lines.
>
> (3) I work a bit with the compat-wireless group, and they've managed to come up with a loadable module that provides "shim" functionality that allows the most recent wireless (wifi) drivers to load and run against older kernels.  I can use a 2.6.37 driver with a 2.6.27 kernel (even with the skb changes that occurred in the interim).
>
> It should be possible to do something similar for click.
>
> The only substantive change is adding new member fields to netdevice.h.
>
> What about using a Makefile adaptation like:
>
> %.o: %.c:
>        (echo '#ifdef __cplusplus' ; \
>         echo 'extern "C" {' ; \
>         echo '#endif' ; \
>         echo '# 0 "$<"' ; \
>         cat $<  ; \
>         echo '#ifdef __cplusplus' ; \
>         echo '}' ; \
>         echo '#endif' ) | $(CC) $(CFLAGS) -c - -o $@
>
>
> to bracket the contents of C files with:
>
> #ifdef __cplusplus
> extern "C" {
> #endif
> ...
> #ifdef __cplusplus
> }
> #endif
>
> and compile them that way?
>
> I'm not sure if the debugging symbols would still be valid, or if they'd point to the wrong source files, but there are ways to patch that up with objcopy.
>
> Comments?
>
> Thanks,
>
> -Philip
>
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