Re: [PATCH v7 2/6] of: overlay: global sysfs enable attribute

A throw once master enable switch to protect against any
further overlay applications if the administrator desires so.

A kernel command line option is provided as well.

Signed-off-by: Pantelis Antoniou <pantelis.antoniou-OWPKS81ov/FWk0Htik3J/w@public.gmane.org>
---
 drivers/of/overlay.c | 50 +++++++++++++++++++++++++++++++++++++++++++++++++-
 1 file changed, 49 insertions(+), 1 deletion(-)

diff --git a/drivers/of/overlay.c b/drivers/of/overlay.c
index 12c3e47..91f10ed 100644
--- a/drivers/of/overlay.c
+++ b/drivers/of/overlay.c

@@ -21,6 +21,7 @@
 #include <linux/err.h>
 #include <linux/idr.h>
 #include <linux/sysfs.h>
+#include <linux/atomic.h>
 
 #include "of_private.h"
 

@@ -55,8 +56,19 @@ struct of_overlay {
 	struct kobject kobj;
 };
 
+/* master enable switch; once set to 0 can't be re-enabled */
+static atomic_t ov_enable = ATOMIC_INIT(1);
+
+static int __init of_overlay_disable_setup(char *str __always_unused)
+{
+	atomic_set(&ov_enable, 0);
+	return 1;
+}
+__setup("of_overlay_disable", of_overlay_disable_setup);
+
 static int of_overlay_apply_one(struct of_overlay *ov,
 		struct device_node *target, const struct device_node *overlay);
+static int overlay_removal_is_ok(struct of_overlay *ov);
 
 static int of_overlay_apply_single_property(struct of_overlay *ov,
 		struct device_node *target, struct property *prop)

@@ -339,6 +351,35 @@ void of_overlay_release(struct kobject *kobj)
 	kfree(ov);
 }
 
+static ssize_t enable_show(struct kobject *kobj,
+		struct kobj_attribute *attr, char *buf)
+{
+	return snprintf(buf, PAGE_SIZE, "%d\n", atomic_read(&ov_enable));