hwrng: core - Reset user selected rng by writing "" to rng_current

User is able to select a chosen rng by writing its name to rng_current
but there is no way to reset it without unbinding the rng. Let user
write "" to rng_current and delesect the chosen rng.

Signed-off-by: PrasannaKumar Muralidharan <prasannatsmkumar@gmail.com>
reviewed-by: Harald Freudenberger <freude@linux.vnet.ibm.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

diff --git a/drivers/char/hw_random/core.c b/drivers/char/hw_random/core.c
index ff79844..657b877 100644 (file)
--- a/drivers/char/hw_random/core.c
+++ b/drivers/char/hw_random/core.c
@@ -292,26 +292,48 @@ static struct miscdevice rng_miscdev = {
        .groups         = rng_dev_groups,
 };
 
+static int enable_best_rng(void)
+{
+       int ret = -ENODEV;
+
+       BUG_ON(!mutex_is_locked(&rng_mutex));
+
+       /* rng_list is sorted by quality, use the best (=first) one */
+       if (!list_empty(&rng_list)) {
+               struct hwrng *new_rng;
+
+               new_rng = list_entry(rng_list.next, struct hwrng, list);
+               ret = ((new_rng == current_rng) ? 0 : set_current_rng(new_rng));
+               if (!ret)
+                       cur_rng_set_by_user = 0;
+       }
+
+       return ret;
+}
+
 static ssize_t hwrng_attr_current_store(struct device *dev,
                                        struct device_attribute *attr,
                                        const char *buf, size_t len)
 {
-       int err;
+       int err = -ENODEV;
        struct hwrng *rng;
 
        err = mutex_lock_interruptible(&rng_mutex);
        if (err)
                return -ERESTARTSYS;
-       err = -ENODEV;
-       list_for_each_entry(rng, &rng_list, list) {
-               if (sysfs_streq(rng->name, buf)) {
-                       err = 0;
-                       cur_rng_set_by_user = 1;
-                       if (rng != current_rng)
+
+       if (sysfs_streq(buf, "")) {
+               err = enable_best_rng();
+       } else {
+               list_for_each_entry(rng, &rng_list, list) {
+                       if (sysfs_streq(rng->name, buf)) {
+                               cur_rng_set_by_user = 1;
                                err = set_current_rng(rng);
-                       break;
+                               break;
+                       }
                }
        }
+
        mutex_unlock(&rng_mutex);
 
        return err ? : len;
@@ -493,17 +515,8 @@ void hwrng_unregister(struct hwrng *rng)
        mutex_lock(&rng_mutex);
 
        list_del(&rng->list);
-       if (current_rng == rng) {
-               drop_current_rng();
-               cur_rng_set_by_user = 0;
-               /* rng_list is sorted by quality, use the best (=first) one */
-               if (!list_empty(&rng_list)) {
-                       struct hwrng *new_rng;
-
-                       new_rng = list_entry(rng_list.next, struct hwrng, list);
-                       set_current_rng(new_rng);
-               }
-       }
+       if (current_rng == rng)
+               enable_best_rng();
 
        if (list_empty(&rng_list)) {
                mutex_unlock(&rng_mutex);