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

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Message-Id: <1232386050.9571.628.camel@quoit>
Date:	Mon, 19 Jan 2009 17:27:30 +0000
From:	Steven Whitehouse <swhiteho@...hat.com>
To:	Randy Dunlap <randy.dunlap@...cle.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, cluster-devel@...hat.com
Subject: Re: mmotm 2009-01-14-20-31 uploaded (gfs2)

Hi,

On Mon, 2009-01-19 at 09:05 -0800, Randy Dunlap wrote:
> Steven Whitehouse wrote:
> > Hi,
> > 
> > On Fri, 2009-01-16 at 09:35 -0800, Andrew Morton wrote:
> >> 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.
> >>
> > Having looked into this in a bit more detail now, it seems that this
> > particular function (generic_setlease) is one of a number appearing in
> > fs.h which are replaced by macros in the case that CONFIG_FILE_LOCKING
> > is not set.
> > 
> > So rather than just do the one function, it seemed to make sense to me
> > to make them all the same. So this uses inline functions as originally
> > proposed. If you'd prefer that we don't inline them and instead have a
> > fs/no-locks.c or something like that with stub functions in it, then I"m
> > happy to revise the patch accordingly.
> 
> Acked-by/Tested-by: Randy Dunlap <randy.dunlap@...cle.com>
> 
Ok, Thanks. I'll send a proper patch to a suitable tree. Presumably the
VFS tree would be best for this?

> > This patch passes my compile tests, modulo a small change that I need to
> > make in GFS2 to suppress a warning (not attached). That seems to be
> > related to yet another set of macros which appear only with
> > CONFIG_FILE_LOCKING not set. Maybe I should update those to be inline
> > functions as well....
> 
> You mean these?  Probably should update them as well.
> 
> #else /* !CONFIG_FILE_LOCKING */
> #define locks_mandatory_locked(a) ({ 0; })
> #define locks_mandatory_area(a, b, c, d, e) ({ 0; })
> #define __mandatory_lock(a) ({ 0; })
> #define mandatory_lock(a) ({ 0; })
> #define locks_verify_locked(a) ({ 0; })
> #define locks_verify_truncate(a, b, c) ({ 0; })
> #define break_lease(a, b) ({ 0; })
> #endif /* CONFIG_FILE_LOCKING */
> 
> 
Yes, I'll do a patch for those as well then,

Steve.


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