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SubjectRe: [PATCH 5/6] i386 virtualization - Make generic set wrprotect a macro
Adrian Bunk wrote:

>On Mon, Aug 15, 2005 at 04:00:39PM -0700, zach@vmware.com wrote:
>
>
>
>>Make the generic version of ptep_set_wrprotect a macro. This is good for
>>code uniformity, and fixes the build for architectures which include pgtable.h
>>through headers into assembly code, but do not define a ptep_set_wrprotect
>>function.
>>
>>
>
>
>This against the kernel coding style.
>In fact, we are usually doing exactly the opposite.
>
>What exactly is the technical problem this patch is trying to solve, IOW
>which architectures are breaking for you?
>
>

The generic pgtable.h include is special and apparently deliberately
against kernel coding style. Look at the rest of the file. All
"functions" here are purely macros, or encapsulated with:

#ifndef __ASSEMBLY__
static inline void foo()
#endif

This is because asm-generic/pgtable.h can get included in assembler
files via a number of ways.

Now, if you have a header file that gets conditionally excluded based on
#ifndef __ASSEMBLY__, as asm-i386/pgtable.h does to
pgtable-{2|3}level.h you must do one of the following:

1) move all __HAVE_ARCH_PTEP_XXX definitions out of the !__ASSEMBLY__
clause
2) protect all inline assembler functions in asm-generic/pgtable.h with
!__ASSEMBLY
3) use macros instead of inline functions in asm-generic

Having the ability to redefine page table accessors at the sub-arch
level is necessary to have a paravirtualized sub-arch of i386. My third
attempt at this (the first was a horror unthinkable to even publish) is
trying to make the code as clean and consistent as possible. #1 above
makes maintaing compile time PAE for i386 with a paravirtualized
sub-arch cumbersome, since one must either isolate the __HAVE_ARCH _XXX
defines from the XXX function definition itself, surround each
individual function with !__ASSEMBLY__, or switch to macros instead of
inline functions for include/asm-i386/pgtable-{2|3}level.h. Ugly and
difficult to maintain.

Thus, I chose the default convention of following the surrounding code.
There are 6 C inline functions in the generic pgtable.h and 37 macros.
Converting to and from macros and inline functions here is rather
tedious and error prone, all of these functions are conditionally
defined based on the architecture, and I don't want to risk introducing
yet another regression for an architecture that I don't have a
cross-compile set up for.

If you have a better approch, I'd be interested in hearing it.

Zach
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