core_param() for genuinely core kernel parameters

There are a lot of one-liner uses of __setup() in the kernel: they're
cumbersome and not queryable (definitely not settable) via /sys.  Yet
it's ugly to simplify them to module_param(), because by default that
inserts a prefix of the module name (usually filename).

So, introduce a "core_param".  The parameter gets no prefix, but
appears in /sys/module/kernel/parameters/ (if non-zero perms arg).  I
thought about using the name "core", but that's more common than
"kernel".  And if you create a module called "kernel", you will die
a horrible death.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

2 files changed, 26 insertions, 7 deletions

diff --git a/include/linux/moduleparam.h b/include/linux/moduleparam.h
index 1eefe6d61b86..e4af3399ef48 100644
--- a/include/linux/moduleparam.h
+++ b/include/linux/moduleparam.h
@@ -104,6 +104,25 @@ struct kparam_array
 #define module_param(name, type, perm)                          \
         module_param_named(name, name, type, perm)
 
+#ifndef MODULE
+/**
+ * core_param - define a historical core kernel parameter.
+ * @name: the name of the cmdline and sysfs parameter (often the same as var)
+ * @var: the variable
+ * @type: the type (for param_set_##type and param_get_##type)
+ * @perm: visibility in sysfs
+ *
+ * core_param is just like module_param(), but cannot be modular and
+ * doesn't add a prefix (such as "printk.").  This is for compatibility
+ * with __setup(), and it makes sense as truly core parameters aren't
+ * tied to the particular file they're in.
+ */
+#define core_param(name, var, type, perm)                               \
+        param_check_##type(name, &(var));                               \
+        __module_param_call("", name, param_set_##type, param_get_##type, \
+                            &var, perm)
+#endif /* !MODULE */
+
 /* Actually copy string: maxlen param is usually sizeof(string). */
 #define module_param_string(name, string, len, perm)                    \
         static const struct kparam_string __param_string_##name         \
diff --git a/kernel/params.c b/kernel/params.c
index f27c992a4625..b077f1b045d3 100644
--- a/kernel/params.c
+++ b/kernel/params.c
@@ -637,14 +637,14 @@ static void __init param_sysfs_builtin(void)
 
                 dot = strchr(kp->name, '.');
                 if (!dot) {
-                        DEBUGP("couldn't find period in first %d characters "
-                               "of %s\n", MODULE_NAME_LEN, kp->name);
-                        continue;
+                        /* This happens for core_param() */
+                        strcpy(modname, "kernel");
+                        name_len = 0;
+                } else {
+                        name_len = dot - kp->name + 1;
+                        strlcpy(modname, kp->name, name_len);
                 }
-                name_len = dot - kp->name;
-                strncpy(modname, kp->name, name_len);
-                modname[name_len] = '\0';
-                kernel_add_sysfs_param(modname, kp, name_len+1);
+                kernel_add_sysfs_param(modname, kp, name_len);
         }
 }