linux-kernel - Re: moduleparam: introduce core_param

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Message-ID: <20161121073747.GA23523@packer-debian-8-amd64.digitalocean.com>
Date:   Mon, 21 Nov 2016 02:37:47 -0500
From:   Jessica Yu <jeyu@...hat.com>
To:     Paul Gortmaker <paul.gortmaker@...driver.com>
Cc:     linux-kernel@...r.kernel.org, Rusty Russell <rusty@...tcorp.com.au>
Subject: Re: moduleparam: introduce core_param_named macro for non-modular
 code

+++ 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@...hat.com>
>Cc: Rusty Russell <rusty@...tcorp.com.au>
>Signed-off-by: Paul Gortmaker <paul.gortmaker@...driver.com>
>---
>
>[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
>