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Date: Tue, 25 Sep 2012 23:12:33 +0200
From: Richard Weinberger <richard@nod.at>
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Subject: Re: [PATCH/resend/bypass] um: Preinclude
 include/linux/kern_levels.h
To: Geert Uytterhoeven <geert@linux-m68k.org>
Cc: Al Viro <viro@zeniv.linux.org.uk>, Linus Torvalds <torvalds@linux-foundation.org>, Joe Perches <joe@perches.com>, user-mode-linux-devel@lists.sourceforge.net, linux-kernel@vger.kernel.org
List-ID: <user-mode-linux-devel.lists.sourceforge.net>

Am Tue, 25 Sep 2012 22:37:13 +0200
schrieb Geert Uytterhoeven <geert@linux-m68k.org>:

> On Tue, Sep 25, 2012 at 9:43 PM, Al Viro <viro@zeniv.linux.org.uk>
> wrote:
> > On Tue, Sep 25, 2012 at 12:20:55PM -0700, Linus Torvalds wrote:
> >> IOW, this part of the patch:
> >>
> >> -       c_flags = -Wp,-MD,$(depfile) $(USER_CFLAGS) -include user.h
> >> $(CFLAGS_$(basetarget).o)
> >> +       c_flags = -Wp,-MD,$(depfile) $(USER_CFLAGS) -include
> >> $(srctree)/include/linux/kern_levels.h -include user.h
> >> $(CFLAGS_$(basetarget).o)
> >>
> >> just makes me go want to puke. The user.h file already has other
> >> #include's in it, so I really don't see why you create this insane
> >> special case.
> >>
> >> And why does UM have those "UM_KERN_XYZ" defines in the first
> >> place? Why isn't it just using KERN_XYZ directly? Is it because
> >> kern_levels.h didn't use to exist, so it was some kind of "let's
> >> create our own that we can hide in our special headers".
> >
> > Because user.h is included *without* kernel headers in include path.
> 
> Indeed.
> 
> > It's for the stuff that is compiled with host libc headers.  Keep in
> > mind that UML talks to libc like normal architecture would talk to
> > hardware.  IOW, analogs of asm glue are in (host) userland C.  And
> > they need libc headers instead of the kernel ones.  That's what that
> > USER_OBJ thing is about.  Kernel-side constants, etc. are delivered
> > to that sucker using the same mechanism we normally use to give them
> > to assembler - asm-offsets.c.  And here, of course, slapping ifndef
> > __ASSEMBLER__ around the tricky bits will not work - the header
> > itself is just fine, but getting kernel headers in the search path
> > really isn't.
> >
> >         I agree that proposed solution is ugly.  What we can do is
> > copy the damn header into include/generated and #include
> > <generated/kern_levels.h> from user.h.  And kill UM_KERN_...
> > stuff.  Objections?
> 
> My first submission had "We may convert all UM_KERN_* users to KERN_*
> and drop the extra defines?" as a suggestion, but so far I haven't
> found time to implement that...
> 
> Still, no one came up with a better patch, and this is a regression.

Yeah, I'd like to take the "ugly" patch to get rid of the regresion.
Later we can get rid of UM_KERN_*, which is IMHO also very ugly.

Thanks,
//richard