linux-kernel - Re: 8250.nr_uarts broken in 3.7

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Date:	Sat, 09 Mar 2013 15:14:18 +0100
From:	Jiri Slaby <jslaby@...e.cz>
To:	Josh Boyer <jwboyer@...hat.com>
CC:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	linux-serial@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: 8250.nr_uarts broken in 3.7

On 03/09/2013 02:30 PM, Josh Boyer wrote:
> From: Josh Boyer <jwboyer@...hat.com>
> Date: Fri, 8 Mar 2013 21:13:52 -0500
> Subject: [PATCH] serial: 8250: Keep 8250.<xxxx> module options functional
>  after driver rename
> 
> With commit 835d844d1 (8250_pnp: do pnp probe before legacy probe), the
> 8250 driver was renamed to 8250_core.  This means any existing usage of
> the 8259.<xxxx> module parameters or as a kernel command line switch is
> now broken, as the 8250_core driver doesn't parse options belonging to
> something called "8250".
> 
> To solve this, we redefine the module options in a dummy function using
> a redefined MODULE_PARAM_PREFX when built into the kernel.  In the case
> where we're building as a module, we provide an alias to the old 8250
> name.  The dummy function prevents compiler errors due to global variable
> redefinitions that happen as part of the module_param_ macro expansions.
> 
> Signed-off-by: Josh Boyer <jwboyer@...hat.com>
> ---
>  drivers/tty/serial/8250/8250.c | 31 +++++++++++++++++++++++++++++++
>  1 file changed, 31 insertions(+)
> 
> diff --git a/drivers/tty/serial/8250/8250.c b/drivers/tty/serial/8250/8250.c
> index 0efc815..446beb7 100644
> --- a/drivers/tty/serial/8250/8250.c
> +++ b/drivers/tty/serial/8250/8250.c
> @@ -3396,3 +3396,34 @@ module_param_array(probe_rsa, ulong, &probe_rsa_count, 0444);
>  MODULE_PARM_DESC(probe_rsa, "Probe I/O ports for RSA");
>  #endif
>  MODULE_ALIAS_CHARDEV_MAJOR(TTY_MAJOR);
> +
> +#ifndef MODULE
> +/* This module was renamed to 8250_core in 3.7.  Keep the old "8250" name
> + * working as well for the module options so we don't break people.  We
> + * need to keep the names identical and the convenient macros will happily
> + * refuse to let us do that by failing the build with redefinition errors
> + * of global variables.  So we stick them inside a dummy function to avoid
> + * those conflicts.  The options still get parsed, and the redefined
> + * MODULE_PARAM_PREFIX lets us keep the "8250." syntax alive.  We redefine
> + * __param_check to a throw away value to avoid type conflicts from the
> + * expansion that would happen otherwise.
> + *
> + * This is hacky.  I'm sorry.
> + */
> +static void __used s8250_options(void)
> +{
> +#undef MODULE_PARAM_PREFIX
> +#define MODULE_PARAM_PREFIX "8250."
> +
> +	module_param_cb(share_irqs, &param_ops_uint, &share_irqs, 0644);
> +	module_param_cb(nr_uarts, &param_ops_uint, &nr_uarts, 0644);
> +	module_param_cb(skip_txen_test, &param_ops_uint, &skip_txen_test, 0644);
> +#ifdef CONFIG_SERIAL_8250_RSA
> +#undef __param_check
> +#define __param_check(name, p, type) int __attribute((unused)) tmp
> +	module_param_array(probe_rsa, ulong, &probe_rsa_count, 0444);

Aiee, we havo no _cb for arrays. But we can do just:
__module_param_call(MODULE_PARAM_PREFIX, probe_rsa,
       &param_array_ops, .arr = &__param_arr_probe_rsa,
       0444, -1);

> +#endif
> +}
> +#else
> +MODULE_ALIAS("8250");

This is so disgusting that I will do the following:
* ack your patch after you change the above (if that works)
* rename 8250.c to 8250_core.c
* change 8250_core.ko back to 8250.ko (ie. bring back the old module name)
* thus switch MODULE_PARAM_PREFIX above to "8250_core."
* deprecate all the newly added 8250_core.* params somehow and schedule
for removal. IMO this warrants a kernel config option like
CONFIG_8250_DEPRECATED_MODULE_PARAMS.

We have a lesson learned.

thanks,
-- 
js
suse labs
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