linux-kernel - Re: [PATCH v5 7/7] fbdev: Make registered

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Date:   Thu, 12 May 2022 20:32:14 +0200
From:   Sam Ravnborg <sam@...nborg.org>
To:     Javier Martinez Canillas <javierm@...hat.com>
Cc:     Guenter Roeck <linux@...ck-us.net>, linux-kernel@...r.kernel.org,
        dri-devel@...ts.freedesktop.org, linux-fbdev@...r.kernel.org,
        Daniel Vetter <daniel.vetter@...ll.ch>,
        Helge Deller <deller@....de>,
        Thomas Zimmermann <tzimmermann@...e.de>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        kernel test robot <lkp@...el.com>,
        Jens Frederich <jfrederich@...il.com>,
        Jon Nettleton <jon.nettleton@...il.com>,
        linux-staging@...ts.linux.dev,
        Daniel Vetter <daniel.vetter@...el.com>,
        Daniel Vetter <daniel@...ll.ch>,
        Matthew Wilcox <willy@...radead.org>,
        Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>,
        Zhen Lei <thunder.leizhen@...wei.com>,
        Alex Deucher <alexander.deucher@....com>,
        Xiyu Yang <xiyuyang19@...an.edu.cn>,
        Zheyu Ma <zheyuma97@...il.com>
Subject: Re: [PATCH v5 7/7] fbdev: Make registered_fb[] private to fbmem.c

On Wed, May 11, 2022 at 07:34:38PM +0200, Javier Martinez Canillas wrote:
> Hello Guenter,
> 
> On 5/11/22 19:17, Guenter Roeck wrote:
> > On 5/11/22 10:00, Sam Ravnborg wrote:
> 
> [snip]
> 
> >>>   struct fb_info *registered_fb[FB_MAX] __read_mostly;
> >>> -EXPORT_SYMBOL(registered_fb);
> >>> -
> >>>   int num_registered_fb __read_mostly;
> >>> +#if IS_ENABLED(CONFIG_FB_OLPC_DCON)
> >>> +EXPORT_SYMBOL(registered_fb);
> >>>   EXPORT_SYMBOL(num_registered_fb);
> >>> +#endif
> >>
> >> It is stuff like this I refer to as "ugly" in the comment above.
> >>
> > 
> > My "solution" for that kind of thing is to use a namespace,
> > such as
> > 
> > EXPORT_SYMBOL_NS(registered_fb, FB_OLPC_DCON);
> > EXPORT_SYMBOL_NS(num_registered_fb, FB_OLPC_DCON);
> >
> 
> Using a namespace in this case is indeed a great idea I think.
> 
> I've used in the past to limit the export of a symbol for within a driver
> that could be scattered across different compilations units, but it never
> occurred to me using it to limit symbols exported by core code.
>  
> > and import it from the offending code. That avoids ifdefs
> > while at the same time limiting the use of the symbols
> > to the expected scope. Of course that could be abused but
> > that abuse would be obvious.
> >
> 
> Agreed. For the next revision, besides using an namespaced export symbol
> as you suggested, I'll include a comment to make clear that it shouldn't
> by any other driver and FB_OLPC_DCON fixed instead.
A very nice compromise, thanks Guenter and Javier.

	Sam