init.h: Add early_param_on_off()

At times all you need is a kconfig variable to enable a feature,
by default but you may want to also enable / disable it through
a kernel parameter. In such cases the parameter routines to turn
the thing on / off are really simple. Just use a wrapper for
this, it lets us generalize the code and makes it easier to
associate parameters with related kernel configuration options.

Signed-off-by: Luis R. Rodriguez <mcgrof@suse.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Borislav Petkov <bp@suse.de>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: David Vrabel <david.vrabel@citrix.com>
Cc: Dexuan Cui <decui@microsoft.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: JBeulich@suse.com
Cc: Jan Beulich <JBeulich@suse.com>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: Juergen Gross <jgross@suse.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Pavel Machek <pavel@ucw.cz>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Tony Lindgren <tony@atomide.com>
Cc: Toshi Kani <toshi.kani@hp.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Xishi Qiu <qiuxishi@huawei.com>
Cc: julia.lawall@lip6.fr
Link: http://lkml.kernel.org/r/1425518654-3403-4-git-send-email-mcgrof@do-not-panic.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>

include/linux/init.h

@@ -268,6 +268,21 @@ struct obs_kernel_param {
 #define early_param(str, fn)					\
 	__setup_param(str, fn, fn, 1)
 
+#define early_param_on_off(str_on, str_off, var, config)			\
+	int var = IS_ENABLED(config);				\
+	static int __init parse_##var##_on(char *arg)		\
+	{							\
+		var = 1;					\
+		return 0;					\
+	}							\
+	static int __init parse_##var##_off(char *arg)		\
+	{							\
+		var = 0;					\
+		return 0;					\
+	}							\
+	__setup_param(str_on, parse_##var##_on, parse_##var##_on, 1); \
+	__setup_param(str_off, parse_##var##_off, parse_##var##_off, 1)
+
 /* Relies on boot_command_line being set */
 void __init parse_early_param(void);
 void __init parse_early_options(char *cmdline);