linux-kernel - Re: [PATCH 2/2] Replace the dangerous to_root

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Date:	Thu, 6 Jan 2011 12:52:59 -0800
From:	Greg KH <gregkh@...e.de>
To:	Ferenc Wagner <wferi@...f.hu>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] Replace the dangerous to_root_device macro with an
 inline function

On Thu, Jan 06, 2011 at 09:47:08PM +0100, Ferenc Wagner wrote:
> Greg KH <gregkh@...e.de> writes:
> 
> > On Thu, Jan 06, 2011 at 04:24:24PM +0100, Ferenc Wagner wrote:
> >
> >> The original macro worked only when applied to variables named 'dev'.
> >> While this could have been fixed by simply renaming the macro argument,
> >> a more type-safe replacement is preferred.
> >
> > Preferred for what?  This is a local macro, not exported to anything
> > else, is it causing problems today within this single file?
> 
> No, it isn't a problem currently, because this macro is applied to
> variables named 'dev' exclusively.  But the macro definition is wrong,
> as it uses 'dev' (the macro argument) in two places, of which the second
> probably isn't intentional, as the third argument of the container_of
> macro is a structure member name, which should stay fixed to the literal
> string 'dev' in this case, not replaced by the actual macro argument.

No, it was intentional :)

> So you've got the choice of leaving things as they are and happen to
> work for the moment, fixing the definition of the to_root_device macro
> to use some other token as the name of the free variable instead of
> 'dev', or to replace the macro with a function, which provides some
> type-checking advantages during compilation as well.  I thought this was
> a general reason for preferring inline functions over preprocessor
> macros in the kernel codebase, but maybe I was wrong.

No, you are correct, but as this is a macro that is limited to a single
file, and there's no problem with it as-is today, the need to change it
is quite low.

I'll take this as a general "clean up" patch, if you resend it with the
2/2 removed.  But note that it will not get added to my trees until
after the .38-rc1 merge happens.

thanks,

greg k-h
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