Re: swapper_space export

[Andrew Morton <akpm@osdl.org>]

Arjan van de Ven <arjan@infradead.org> wrote:
>
> On Tue, 2006-05-16 at 19:24 -0400, Josef Sipek wrote:
> > I was trying to compile the Unionfs[1] to get it up to sync it up with
> > the kernel developments from the past few months. Anyway, long story
> > short...swapper_space (defined in mm/swap_state.c) is not exported
> > anymore (git commit: 4936967374c1ad0eb3b734f24875e2484c3786cc). This
> > apparently is not an issue for most modules. Troubles arise when the
> > modules include mm.h or any of its relatives.
> > 
> > One simply gets a linker error about swapper_space not being defined.
> > The problem is that it is used in mm.h.
> 
> 
> don't you think it's really suspect that no other filesystem, in fact no
> other driver in the kernel needs this? Could it just be that unionfs is 
> using a wrong API ? Because if that's the case you're patch is just the
> wrong thing. Maybe the unionfs people should try to submit their code
> for review etc......

They're probably just using page_mapping(), which is a reasonable thing to so.

Probably it's sufficient to use page->mapping.  It depends how they got
hold of the page.  If it's know to be in filesystem pagecache then
page->mapping will be OK.