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 <fre...@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

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