linux-kernel - Re: mmotm 2009-01-14-20-31 uploaded (gfs2)

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Message-Id: <20090116093550.ce7229d5.akpm@linux-foundation.org>
Date:	Fri, 16 Jan 2009 09:35:50 -0800
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Randy Dunlap <randy.dunlap@...cle.com>
Cc:	Steven Whitehouse <swhiteho@...hat.com>,
	linux-kernel@...r.kernel.org, cluster-devel@...hat.com
Subject: Re: mmotm 2009-01-14-20-31 uploaded (gfs2)

On Fri, 16 Jan 2009 09:06:23 -0800 Randy Dunlap <randy.dunlap@...cle.com> wrote:

> >>> which is not ideal, but I don't see any easy way to avoid the #ifdef,
> >>>
> >> Take a look in fs.h:
> >>
> >> #define generic_setlease(a, b, c) ({ -EINVAL; })
> >>
> >> If that wasn't a stupid macro, your code would have compiled and ran
> >> just as intended.
> >>
> > There doesn't seem to be an easy answer though. If I #define it to NULL,
> > that upsets other parts of the code that rely on that macro, and if I
> > turn it into a inline function which returns -EINVAL, then presumably I
> > can't take its address for my file_operations.
> 
> No, gcc will allow &inline_func and out-of-line it if it is needed (AFAIK;
> I've seen a few cases of that).
> 

yup.  It measn that we'll get a separate private copy of the
generic_setlease() code in each compilation unit which takes its
address, but I don't think that would kill us.

The prevention is of course to put the stub function in a core kernel
.c file and export it to modules.

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