Re: potential linking bug in recursive directory descent

[Sam Ravnborg <sam@ravnborg.org>]

On Tue, Feb 24, 2009 at 04:20:01PM -0500, Fred Isaman wrote:
> On Tue, Feb 24, 2009 at 4:03 PM, Sam Ravnborg <sam@ravnborg.org> wrote:
> > On Tue, Feb 24, 2009 at 02:05:25PM -0500, Fred Isaman wrote:
> >> The pnfs tree base of of 2.6.29-rc5 uses the new find_last_bit
> >> function (defined in
> >> lib/find_last_bit.c) in a file in the fs/nfs directory.  Myself and
> >> another developer (though no one else so far) get the following error
> >> during compile:
> >>
> >>    Kernel: arch/x86/boot/bzImage is ready  (#5)
> >>      Building modules, stage 2.
> >>      MODPOST 515 modules
> >>    ERROR: "find_last_bit" [fs/nfs/nfs.ko] undefined!
> >>    make[2]: *** [__modpost] Error 1
> >>    make[1]: *** [modules] Error 2
> >>    make: *** [sub-make] Error 2
> >>
> >>
> >> Note that find_last_bit() is not used in any file in the fs directory.
> >> If I add it to any function that is EXPORT_SYMBOL'ed
> >> from the fs directory, suddenly the compile errors go away.  (See the
> >> below patch for a more concrete example.)
> >>
> >> I am not sure what is going on, and why it only affects some
> >> developers, but it looks a lot like the kbuild system
> >> is deciding that the library does not need to be included at the fs
> >> directory level, so isn't including it in fs/nfs where
> >> it is needed.
> >
> > kbuild only links in libaries if there is any users of siad library.
> > And your normal config has no users of lib/find_last_bit.c so
> > it is not linked into the kernel.
> >
> 
> I don't understand your comment.  There *is* a user of the library in the
> (modified) fs/nfs/nfs4proc.c.  The problem is that it doesn't compile unless
> there is also a user in some fs/*.c.

There need to be an in-kernel user and I expect fs/nfs/nfs4proc.c is
build as a module.

	Sam