linux-kernel - Re: [RFC][PATCH] module: allow multiple calls to MODULE_DEVICE

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Message-ID: <87mwigzy6a.fsf@rustcorp.com.au>
Date:	Tue, 28 Jan 2014 12:04:53 +1030
From:	Rusty Russell <rusty@...tcorp.com.au>
To:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Tom Gundersen <teg@...m.no>
Cc:	linux-kernel@...r.kernel.org, linux-input@...r.kernel.org,
	kay@...y.org, Dmitry Torokhov <dmitry.torokhov@...il.com>
Subject: Re: [RFC][PATCH] module: allow multiple calls to MODULE_DEVICE_TABLE() per module

Greg Kroah-Hartman <gregkh@...uxfoundation.org> writes:
> On Mon, Jan 27, 2014 at 08:09:55PM +0100, Tom Gundersen wrote:
>> Commit 78551277e4df5: "Input: i8042 - add PNP modaliases" had a bug, where the
>> second call to MODULE_DEVICE_TABLE() overrode the first resulting in not all
>> the modaliases being exposed.
>> 
>> This fixes the problem by including the name of the device_id table in the
>> __mod_*_device_table alias, allowing us to export several device_id tables
>> per module.
>> 
>> Suggested-by: Kay Sievers <kay@...y.org>
>> Cc: Dmitry Torokhov <dmitry.torokhov@...il.com>
>> Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
>> Cc: Rusty Russell <rusty@...tcorp.com.au>
>> ---
>>  include/linux/module.h   |  2 +-
>>  scripts/mod/file2alias.c | 14 +++++++++-----
>>  2 files changed, 10 insertions(+), 6 deletions(-)
>
> Ah, very nice, I've wanted this for a while now, it would make a number
> of different drivers much smaller and simpler to add new device ids to
> (no multiple lists of ids, one for the module loader and one for the
> sub-driver that is in the single file.)

You never asked :(

I've applied, this, but I'm actually amazed this patch works.  C is
weird sometimes.  It changes declarations of the form:

extern const struct pci_device_id __mod_pci_device_id_table
        __attribute__ ((unused, alias("e1000_pci_tbl"));

Into:

extern const struct pci__e1000_pci_tbl_device_id __mod_pci__e1000_pci_tbl_device_id_table
        __attribute__ ((unused, alias("e1000_pci_tbl"));

Now, that's a completely unknown type, but gcc doesn't care because it's
just an extern declaration.  It does insert the alias, which is all we
care about.

We would normally use a special section for this, so it's mainly
historical.  Now we have DEFINE_PCI_DEVICE_TABLE etc, we should
use those to put it in a special section (eg. "pci_ids") and
grab that directly.

Volunteers welcome :)
Rusty.
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