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

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

On Thu, Oct 22, 2015 at 10:50:23PM +0300, Pantelis Antoniou wrote:
> 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@konsulko.com>
> ---
>  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));


Anyway, nothing worth keeping this from being merged:

Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>