Re: [PATCH 3/5] of: overlay: Master enable switch

Hi Rob,

On Mar 24, 2015, at 22:25 , Rob Herring [off-list ref] wrote:

On Tue, Mar 17, 2015 at 3:30 PM, Pantelis Antoniou
[off-list ref] wrote:

quoted

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

sysfs documentation?

OK, coming up.

quoted

Signed-off-by: Pantelis Antoniou <redacted>
---
drivers/of/overlay.c | 66 +++++++++++++++++++++++++++++++++++++++++++++++++++-
1 file changed, 65 insertions(+), 1 deletion(-)

diff --git a/drivers/of/overlay.c b/drivers/of/overlay.c
index f17f5ef..6688797 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"

@@ -55,6 +56,9 @@ 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);

@@ -345,6 +349,60 @@ static struct kobj_type of_overlay_ktype = {

static struct kset *ov_kset;

+static ssize_t enable_read(struct file *filp, struct kobject *kobj,
+               struct bin_attribute *bin_attr, char *buf,
+               loff_t offset, size_t count)
+{
+       char tbuf[3];
+
+       if (offset < 0)
+               return -EINVAL;
+
+       if (offset >= sizeof(tbuf))
+               return 0;
+
+       if (count > sizeof(tbuf) - offset)
+               count = sizeof(tbuf) - offset;
+
+       /* fill in temp */
+       tbuf[0] = '0' + atomic_read(&ov_enable);
+       tbuf[1] = '\n';
+       tbuf[2] = '\0';
+
+       /* copy to buffer */
+       memcpy(buf, tbuf + offset, count);
+
+       return count;
+}
+
+static ssize_t enable_write(struct file *filp, struct kobject *kobj,
+               struct bin_attribute *bin_attr, char *buf,
+               loff_t off, size_t count)
+{
+       int new_enable;
+
+       if (off != 0 || (buf[0] != '0' && buf[1] != '1'))

Is buf[1] correct here?

Nope.

quoted

+               return -EINVAL;
+
+       new_enable = buf[0] - '0';
+       if (new_enable != 0 && new_enable != 1)

Make unsigned just "if (new_enable > 1)”.

OK.

quoted

+               return -EINVAL;
+
+       /* NOP for same value */
+       if (new_enable == atomic_read(&ov_enable))
+               return count;
+
+       /* if we've disabled it, no going back */
+       if (atomic_read(&ov_enable) == 0)
+               return -EPERM;
+
+       atomic_set(&ov_enable, new_enable);
+       return count;
+}
+
+/* just a single char + '\n' + '\0' */
+static BIN_ATTR_RW(enable, 3);
+
/**
 * of_overlay_create() - Create and apply an overlay
 * @tree:      Device node containing all the overlays

@@ -360,6 +418,10 @@ 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 +658,7 @@ int of_overlay_init(void)
       if (!ov_kset)
               return -ENOMEM;

-       return 0;
+       rc = sysfs_create_bin_file(&ov_kset->kobj, &bin_attr_enable);
+       WARN(rc, "%s: error adding enable attribute\n", __func__);
+       return rc;

}
--
1.7.12

Regards

— Pantelis