rbd: add 'minor' sysfs rbd device attribute

Introduce /sys/bus/rbd/devices/<id>/minor sysfs attribute for exporting
rbd whole disk minor numbers.  This is a step towards single-major
device number allocation scheme, but also a good thing on its own.

Signed-off-by: Ilya Dryomov <ilya.dryomov@inktank.com>
Reviewed-by: Alex Elder <elder@linaro.org>
Reviewed-by: Josh Durgin <josh.durgin@inktank.com>

2 files changed, 16 insertions, 1 deletions

diff --git a/Documentation/ABI/testing/sysfs-bus-rbd b/Documentation/ABI/testing/sysfs-bus-rbd
index 0a306476424e..17b119c692da 100644
--- a/Documentation/ABI/testing/sysfs-bus-rbd
+++ b/Documentation/ABI/testing/sysfs-bus-rbd
@@ -33,6 +33,10 @@ major
 
         The block device major number.
 
+minor
+
+        The block device minor number.  (December 2013, since 3.14.)
+
 name
 
         The name of the rbd image.
diff --git a/drivers/block/rbd.c b/drivers/block/rbd.c
index d250549d27a4..01ed7672a076 100644
--- a/drivers/block/rbd.c
+++ b/drivers/block/rbd.c
@@ -323,6 +323,7 @@ struct rbd_device {
         int                     dev_id;         /* blkdev unique id */
 
         int                     major;          /* blkdev assigned major */
+        int                     minor;
         struct gendisk          *disk;          /* blkdev's gendisk and rq */
 
         u32                     image_format;   /* Either 1 or 2 */
@@ -3397,7 +3398,7 @@ static int rbd_init_disk(struct rbd_device *rbd_dev)
         snprintf(disk->disk_name, sizeof(disk->disk_name), RBD_DRV_NAME "%d",
                  rbd_dev->dev_id);
         disk->major = rbd_dev->major;
-        disk->first_minor = 0;
+        disk->first_minor = rbd_dev->minor;
         disk->fops = &rbd_bd_ops;
         disk->private_data = rbd_dev;
 
@@ -3469,7 +3470,14 @@ static ssize_t rbd_major_show(struct device *dev,
                 return sprintf(buf, "%d\n", rbd_dev->major);
 
         return sprintf(buf, "(none)\n");
+}
+
+static ssize_t rbd_minor_show(struct device *dev,
+                              struct device_attribute *attr, char *buf)
+{
+        struct rbd_device *rbd_dev = dev_to_rbd_dev(dev);
 
+        return sprintf(buf, "%d\n", rbd_dev->minor);
 }
 
 static ssize_t rbd_client_id_show(struct device *dev,
@@ -3591,6 +3599,7 @@ static ssize_t rbd_image_refresh(struct device *dev,
 static DEVICE_ATTR(size, S_IRUGO, rbd_size_show, NULL);
 static DEVICE_ATTR(features, S_IRUGO, rbd_features_show, NULL);
 static DEVICE_ATTR(major, S_IRUGO, rbd_major_show, NULL);
+static DEVICE_ATTR(minor, S_IRUGO, rbd_minor_show, NULL);
 static DEVICE_ATTR(client_id, S_IRUGO, rbd_client_id_show, NULL);
 static DEVICE_ATTR(pool, S_IRUGO, rbd_pool_show, NULL);
 static DEVICE_ATTR(pool_id, S_IRUGO, rbd_pool_id_show, NULL);
@@ -3604,6 +3613,7 @@ static struct attribute *rbd_attrs[] = {
         &dev_attr_size.attr,
         &dev_attr_features.attr,
         &dev_attr_major.attr,
+        &dev_attr_minor.attr,
         &dev_attr_client_id.attr,
         &dev_attr_pool.attr,
         &dev_attr_pool_id.attr,
@@ -4848,6 +4858,7 @@ static int rbd_dev_device_setup(struct rbd_device *rbd_dev)
         if (ret < 0)
                 goto err_out_id;
         rbd_dev->major = ret;
+        rbd_dev->minor = 0;
 
         /* Set up the blkdev mapping. */