Re: [PATCH v4 2/4] of: overlay: global sysfs enable attribute
From: Rob Herring <hidden>
Date: 2015-09-02 02:44:06
Also in:
linux-api, lkml
On Fri, Jun 12, 2015 at 2:38 PM, Pantelis Antoniou [off-list ref] wrote:
A throw once master enable switch to protect against any further overlay applications if the administrator desires so. Signed-off-by: Pantelis Antoniou <pantelis.antoniou-OWPKS81ov/FWk0Htik3J/w@public.gmane.org>
I had some questioning whether we want more states than just on/off like "only add sub-trees", but I've convinced myself it is better to keep the kill switch simple. So I'm okay with patches 1 and 2 (and the relevant part of 4 if you want to split it). I think #3 needs to be part of how we expect userspace to interact with overlays. Please respin and I will queue at least the kill switch for 4.4 unless there are further comments. Rob
quoted hunk ↗ jump to hunk
--- drivers/of/overlay.c | 43 ++++++++++++++++++++++++++++++++++++++++++- 1 file changed, 42 insertions(+), 1 deletion(-)diff --git a/drivers/of/overlay.c b/drivers/of/overlay.c index f17f5ef..37ec858 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 +56,12 @@ 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 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 +344,35 @@ 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)); +} + +static ssize_t enable_store(struct kobject *kobj, + struct kobj_attribute *attr, const char *buf, size_t count) +{ + int ret; + bool new_enable; + + ret = strtobool(buf, &new_enable); + if (ret != 0) + return ret; + /* if we've disabled it, no going back */ + if (atomic_read(&ov_enable) == 0) + return -EPERM; + atomic_set(&ov_enable, (int)new_enable); + return count; +} + +static struct kobj_attribute enable_attr = __ATTR_RW(enable); + +static const struct attribute *overlay_global_attrs[] = { + &enable_attr.attr, + NULL +}; + static struct kobj_type of_overlay_ktype = { .release = of_overlay_release, };@@ -360,6 +394,10 @@ int of_overlay_create(struct device_node *tree) struct of_overlay *ov; int err, id; + /* administratively disabled */ + if (!atomic_read(&ov_enable)) + return -EPERM; + /* allocate the overlay structure */ ov = kzalloc(sizeof(*ov), GFP_KERNEL); if (ov == NULL)@@ -596,5 +634,8 @@ int of_overlay_init(void) if (!ov_kset) return -ENOMEM; - return 0; + rc = sysfs_create_files(&ov_kset->kobj, overlay_global_attrs); + WARN(rc, "%s: error adding global attributes\n", __func__); + + return rc; } --1.7.12