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?
> 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?
> + return -EINVAL;
> +
> + new_enable = buf[0] - '0';
> + if (new_enable != 0 && new_enable != 1)
Make unsigned just "if (new_enable > 1)".
> + 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
>
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