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

Hi Greg,

On Oct 22, 2015, at 23:19 , Greg Kroah-Hartman [off-list ref] wrote:

On Thu, Oct 22, 2015 at 10:50:23PM +0300, Pantelis Antoniou wrote:

quoted

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));

Minor nit, you never need to care about the size of the buffer for a
sysfs file, if you do, you are doing something wrong.  So this can just
be:
	return sprintf(buf, "%d\n", atomic_read(&ov_enable));

Nice to know; I have a ingrained habit to avoid standard sprintf, so..

Anyway, nothing worth keeping this from being merged:

Thanks!

Acked-by: Greg Kroah-Hartman <redacted>

Regards

— Pantelis