linux-kernel - Re: [PATCH v9 05/10] module.h: MODULE_DEVICE

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Message-ID: <CAJzde04mhRh2SajwdfMTzoDJ_F_Xo_3utfcvxY1Dpgqrv-rzOg@mail.gmail.com>
Date:   Tue, 20 Dec 2022 10:36:37 -0600
From:   Allen Webb <allenwebb@...gle.com>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     "linux-modules@...r.kernel.org" <linux-modules@...r.kernel.org>,
        "linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Luis Chamberlain <mcgrof@...nel.org>,
        "Rafael J. Wysocki" <rafael@...nel.org>
Subject: Re: [PATCH v9 05/10] module.h: MODULE_DEVICE_TABLE for built-in modules

On Tue, Dec 20, 2022 at 12:45 AM Greg Kroah-Hartman
<gregkh@...uxfoundation.org> wrote:
>
> On Mon, Dec 19, 2022 at 02:46:13PM -0600, Allen Webb wrote:
> > Implement MODULE_DEVICE_TABLE for build-in modules to make it possible
> > to generate a builtin.alias file to complement modules.alias.
> >
> > Signed-off-by: Allen Webb <allenwebb@...gle.com>
> > ---
> >  include/linux/module.h | 15 ++++++++++++++-
> >  1 file changed, 14 insertions(+), 1 deletion(-)
> >
> > diff --git a/include/linux/module.h b/include/linux/module.h
> > index ec61fb53979a..3d1b04ca6350 100644
> > --- a/include/linux/module.h
> > +++ b/include/linux/module.h
> > @@ -243,7 +243,20 @@ extern void cleanup_module(void);
> >  extern typeof(name) __mod_##type##__##name##_device_table            \
> >    __attribute__ ((unused, alias(__stringify(name))))
> >  #else  /* !MODULE */
> > -#define MODULE_DEVICE_TABLE(type, name)
> > +/*
> > + * The names may not be unique for built-in modules, so include the module name
> > + * to guarantee uniqueness.
>
> What "names" are you referring to here with the words, "The names"?
>
> And built-in modules have the same rules as external names, they have to
> be unique so I do not understand the problem you are trying to solve
> here, which means you need to describe it better in both the changelog
> text and the comment.

I changed the comment to:
/*
 * Creates an alias so file2alias.c can find device table for built in modules.
 *
 * The module name is included for two reasons:
 *   - Adding the module name to the alias avoids creating two aliases with the
 *     same name. Historically MODULE_DEVICE_TABLE was a no-op for built-in
 *     modules, so there was nothing to stop different modules from having the
 *     same device table name and consequently the same alias when building as a
 *     module.
 *   - The module name is needed by files2alias.c to associate a particular
 *     device table with its associated module since files2alias would otherwise
 *     see the module name as `vmlinuz.o` for built-in modules.
 */

>
> > + *
> > + * Note that extern is needed because modpost reads these symbols to generate
> > + * modalias entries for each match id in each device table. They are not used
> > + * at runtime.
>
> This comment isn't explaining much about what the #define is to be used
> for, is it?

I will drop this. I originally added the comment because Christophe Leroy said:
"'extern' keyword is pointless of function prototypes and deprecated.
Don't add new occurences."

This is clearly not a typical function prototype and the guidance from:
https://www.kernel.org/doc/html/latest/process/coding-style.html#function-prototypes
should not apply.

>
> confused,
>
> greg k-h