Re: moduleparam: introduce core_param_named macro for non-modular code

[Jessica Yu]

+++ Paul Gortmaker [14/11/16 21:00 -0500]:
> We have the case where module_param_named() in file "foo.c" for
> parameter myparam translates that into the bootarg for the
> non-modular use case as "foo.myparam=..."
>
> The problem exists where the use case with the filename and the
> dot prefix is established, but the code is then realized to be 100%
> non-modular, or is converted to non-modular.  Both of the existing
> macros like core_param() or setup_param() do not append such a
> prefix, so a straight conversion to either will break the existing
> use cases.
>
> Similarly, trying to embed a hard coded "foo." prefix on the name
> fails cpp syntax due to the special nature of "." in code.  So we add
> this parallel variant for the modular --> non-modular transition to
> preserve existing and documented use cases with such a prefix.

Hm, I'm not convinced we need a core_ counterpart to module_param_named
(that's nearly identical), when module_param_named already implements
all of the above. Plenty of non-modular code already use it (e.g.
workqueue, printk), and a prefix is automatically supplied (which can be
overridden) in the non-modular case. That should already meet your
requirements, no?

> Cc: Jessica Yu <jeyu@xxxxxxxxxx>
> Cc: Rusty Russell <rusty@xxxxxxxxxxxxxxx>
> Signed-off-by: Paul Gortmaker <paul.gortmaker@xxxxxxxxxxxxx>
> ---
>
> [Marking this RFC since I don't like the fact that it still requires
> non-modular code to use moduleparam.h -- one possible fix for that is
> to consider moving non-modular macros to a new param.h or similar. ]
>
> include/linux/moduleparam.h | 17 +++++++++++++++++
> 1 file changed, 17 insertions(+)
>
> diff --git a/include/linux/moduleparam.h b/include/linux/moduleparam.h
> index 52666d90ca94..4f2b92345eb5 100644
> --- a/include/linux/moduleparam.h
> +++ b/include/linux/moduleparam.h
> @@ -269,6 +269,23 @@ static inline void kernel_param_unlock(struct module *mod)
> 	__module_param_call("", name, &param_ops_##type, &var, perm, -1, 0)
>
> /**
> + * core_param_named - define a module compat core kernel parameter.
> + * @name: the name of the cmdline and sysfs parameter (often the same as var)
> + * @var: the variable
> + * @type: the type of the parameter
> + * @perm: visibility in sysfs
> + *
> + * core_param_named is just like module_param_named(), but cannot be modular
> + * and it _does_ add a prefix (such as "printk.").  This is for compatibility
> + * with module_param_named(), and it exists to provide boot arg compatibility
> + * with code that was previously using the modular version with the prefix.
> + */
> +#define core_param_named(name, var, type, perm)				\
> +	param_check_##type(name, &(var));				\
> +	__module_param_call(KBUILD_MODNAME ".", name, &param_ops_##type,\
> +			    &var, perm, -1, 0)
> +
> +/**
>  * core_param_unsafe - same as core_param but taints kernel
>  */
> #define core_param_unsafe(name, var, type, perm)		\
> --
> 2.10.1