rbd: supported_features bus attribute

... so that userspace can generate meaningful error messages and spell
out unsupported features that need to be disabled.

Signed-off-by: Ilya Dryomov <idryomov@gmail.com>
Reviewed-by: Sage Weil <sage@redhat.com>

1 files changed, 12 insertions, 4 deletions

diff --git a/drivers/block/rbd.c b/drivers/block/rbd.c
index 4d6807723798..517838b65964 100644
--- a/drivers/block/rbd.c
+++ b/drivers/block/rbd.c
@@ -120,10 +120,11 @@ static int atomic_dec_return_safe(atomic_t *v)
 
 /* Feature bits */
 
-#define RBD_FEATURE_LAYERING    (1<<0)
-#define RBD_FEATURE_STRIPINGV2  (1<<1)
-#define RBD_FEATURE_EXCLUSIVE_LOCK (1<<2)
-#define RBD_FEATURE_DATA_POOL (1<<7)
+#define RBD_FEATURE_LAYERING            (1ULL<<0)
+#define RBD_FEATURE_STRIPINGV2          (1ULL<<1)
+#define RBD_FEATURE_EXCLUSIVE_LOCK      (1ULL<<2)
+#define RBD_FEATURE_DATA_POOL           (1ULL<<7)
+
 #define RBD_FEATURES_ALL        (RBD_FEATURE_LAYERING |         \
                                  RBD_FEATURE_STRIPINGV2 |       \
                                  RBD_FEATURE_EXCLUSIVE_LOCK |   \
@@ -499,16 +500,23 @@ static bool rbd_is_lock_owner(struct rbd_device *rbd_dev)
         return is_lock_owner;
 }
 
+static ssize_t rbd_supported_features_show(struct bus_type *bus, char *buf)
+{
+        return sprintf(buf, "0x%llx\n", RBD_FEATURES_SUPPORTED);
+}
+
 static BUS_ATTR(add, S_IWUSR, NULL, rbd_add);
 static BUS_ATTR(remove, S_IWUSR, NULL, rbd_remove);
 static BUS_ATTR(add_single_major, S_IWUSR, NULL, rbd_add_single_major);
 static BUS_ATTR(remove_single_major, S_IWUSR, NULL, rbd_remove_single_major);
+static BUS_ATTR(supported_features, S_IRUGO, rbd_supported_features_show, NULL);
 
 static struct attribute *rbd_bus_attrs[] = {
         &bus_attr_add.attr,
         &bus_attr_remove.attr,
         &bus_attr_add_single_major.attr,
         &bus_attr_remove_single_major.attr,
+        &bus_attr_supported_features.attr,
         NULL,
 };