Hi Rob,
> On Mar 24, 2015, at 22:25 , Rob Herring <robherring2@xxxxxxxxx> wrote:
>
> On Tue, Mar 17, 2015 at 3:30 PM, Pantelis Antoniou
> <pantelis.antoniou@xxxxxxxxxxxx> wrote:
>> Implement a throw once master enable switch to protect against any
>> further overlay applications if the administrator desires so.
>
> sysfs documentation?
>
OK, coming up.
>> Signed-off-by: Pantelis Antoniou <pantelis.antoniou@xxxxxxxxxxxx>
>> ---
>> 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.
>> + return -EINVAL;
>> +
>> + new_enable = buf[0] - '0';
>> + if (new_enable != 0 && new_enable != 1)
>
> Make unsigned just "if (new_enable > 1)”.
>
OK.
>> + 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
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