linux-kernel - Re: [PATCH 1/2] Export get_user_pages

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Message-ID: <20080730170939.GA28604@cs181140183.pp.htv.fi>
Date:	Wed, 30 Jul 2008 20:09:39 +0300
From:	Adrian Bunk <bunk@...nel.org>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Rusty Russell <rusty@...tcorp.com.au>, lguest <lguest@...abs.org>,
	linux-kernel@...r.kernel.org, Nick Piggin <nickpiggin@...oo.com.au>
Subject: Re: [PATCH 1/2] Export get_user_pages_fast

On Wed, Jul 30, 2008 at 10:03:55AM -0700, Andrew Morton wrote:
> On Wed, 30 Jul 2008 18:47:36 +0300 Adrian Bunk <bunk@...nel.org> wrote:
> 
> > On Wed, Jul 30, 2008 at 03:35:23AM -0700, Andrew Morton wrote:
> > > On Wed, 30 Jul 2008 14:38:55 +1000 Rusty Russell <rusty@...tcorp.com.au> wrote:
> > > 
> > > > After all, it was made for lguest wasn't it?  Still think it should be
> > > > called get_current_pages() though.
> > > > 
> > > > Signed-off-by: Rusty Russell <rusty@...tcorp.com.au>
> > > > ---
> > > >  arch/x86/mm/gup.c |    2 ++
> > > >  1 file changed, 2 insertions(+)
> > > > 
> > > > diff -r cb465381f6d5 arch/x86/mm/gup.c
> > > > --- a/arch/x86/mm/gup.c	Wed Jul 30 10:18:44 2008 +1000
> > > > +++ b/arch/x86/mm/gup.c	Wed Jul 30 14:22:53 2008 +1000
> > > > @@ -8,6 +8,7 @@
> > > >  #include <linux/mm.h>
> > > >  #include <linux/vmstat.h>
> > > >  #include <linux/highmem.h>
> > > > +#include <linux/module.h>
> > > >  
> > > >  #include <asm/pgtable.h>
> > > >  
> > > > @@ -296,3 +303,4 @@ slow_irqon:
> > > >  		return ret;
> > > >  	}
> > > >  }
> > > > +EXPORT_SYMBOL_GPL(get_user_pages_fast);
> > > 
> > > A regularly-occurring problem with an export like this is that someone
> > > writes a driver and tests it on x86, then the driver explodes on an
> > > architecture which didn't export the same symbol.
> > > 
> > > So a better implementation might be to put
> > > 
> > > #ifdef CONFIG_HAVE_GET_USER_PAGES_FAST
> > > EXPORT_SYMBOL_GPL(get_user_pages_fast);
> > > #endif
> > > 
> > > into generic code somewhere.
> > 
> > How would that help?
> 
> It would fix the problem which I described.

The export would still only be available on x86 since no other arch 
would define CONFIG_HAVE_GET_USER_PAGES_FAST.

Or what do I miss?

cu
Adrian

-- 

       "Is there not promise of rain?" Ling Tan asked suddenly out
        of the darkness. There had been need of rain for many days.
       "Only a promise," Lao Er said.
                                       Pearl S. Buck - Dragon Seed

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