Re: [PATCH 3/3] crypto: hwrng add sysfs attribute to show user selected rng

[PrasannaKumar Muralidharan <prasannatsmkumar@gmail.com>]

On 3 July 2017 at 15:33, Harald Freudenberger <freude@linux.vnet.ibm.com> wrote:
> This patch introduces a new sysfs attribute file 'rng_selected'
> which shows the the rng chosen by userspace.
>
> If a rng source is chosen by user via echo some valid string
> to rng_current there should be a way to signal this choice to
> userspace. The new attribute file 'rng_selected' shows either
> the name of the rng chosen or 'none'.
>
> Signed-off-by: Harald Freudenberger <freude@linux.vnet.ibm.com>
> ---
>  drivers/char/hw_random/core.c | 22 +++++++++++++++++-----
>  1 file changed, 17 insertions(+), 5 deletions(-)
>
> diff --git a/drivers/char/hw_random/core.c b/drivers/char/hw_random/core.c
> index ffd4e36..6a6276a 100644
> --- a/drivers/char/hw_random/core.c
> +++ b/drivers/char/hw_random/core.c
> @@ -28,8 +28,8 @@
>  #define RNG_MODULE_NAME                "hw_random"
>
>  static struct hwrng *current_rng;
> -/* the current rng has been explicitly chosen by user via sysfs */
> -static int cur_rng_set_by_user;
> +/* the rng explicitly selected by user via sysfs */
> +static struct hwrng *selected_rng;
>  static struct task_struct *hwrng_fill;
>  /* list of registered rngs, sorted decending by quality */
>  static LIST_HEAD(rng_list);
> @@ -306,7 +306,7 @@ static ssize_t hwrng_attr_current_store(struct device *dev,
>         list_for_each_entry(rng, &rng_list, list) {
>                 if (sysfs_streq(rng->name, buf)) {
>                         err = 0;
> -                       cur_rng_set_by_user = 1;
> +                       selected_rng = rng;
>                         if (rng != current_rng)
>                                 err = set_current_rng(rng);
>                         break;
> @@ -355,16 +355,28 @@ static ssize_t hwrng_attr_available_show(struct device *dev,
>         return strlen(buf);
>  }
>
> +static ssize_t hwrng_attr_selected_show(struct device *dev,
> +                                       struct device_attribute *attr,
> +                                       char *buf)
> +{
> +       return snprintf(buf, PAGE_SIZE, "%s\n",
> +                       selected_rng ? selected_rng->name : "none");
> +}
> +
>  static DEVICE_ATTR(rng_current, S_IRUGO | S_IWUSR,
>                    hwrng_attr_current_show,
>                    hwrng_attr_current_store);
>  static DEVICE_ATTR(rng_available, S_IRUGO,
>                    hwrng_attr_available_show,
>                    NULL);
> +static DEVICE_ATTR(rng_selected, S_IRUGO,
> +                  hwrng_attr_selected_show,
> +                  NULL);
>
>  static struct attribute *rng_dev_attrs[] = {
>         &dev_attr_rng_current.attr,
>         &dev_attr_rng_available.attr,
> +       &dev_attr_rng_selected.attr,
>         NULL
>  };
>
> @@ -448,7 +460,7 @@ int hwrng_register(struct hwrng *rng)
>         old_rng = current_rng;
>         err = 0;
>         if (!old_rng ||
> -           (!cur_rng_set_by_user && rng->quality > old_rng->quality)) {
> +           (!selected_rng && rng->quality > old_rng->quality)) {
>                 /*
>                  * Set new rng as current as the new rng source
>                  * provides better entropy quality and was not
> @@ -484,7 +496,7 @@ void hwrng_unregister(struct hwrng *rng)
>         list_del(&rng->list);
>         if (current_rng == rng) {
>                 drop_current_rng();
> -               cur_rng_set_by_user = 0;
> +               selected_rng = NULL;
>                 /* rng_list is sorted by quality, use the best (=first) one */
>                 if (!list_empty(&rng_list)) {
>                         struct hwrng *new_rng;
> --
> 2.7.4
>

The current_rng sysfs attribute shows currently selected rng. So this
new attribute can contain 1 to indicate user's choice, 0 otherwise.

Regards,
PrasannaKumar