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

From: Jessica Yu
Date: Mon Nov 21 2016 - 02:37:53 EST

+++ 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) \