rbd: create pool_id device attribute

Add an entry under /sys/bus/rbd/devices/<N>/ named "pool_id" that
provides the id for the pool the rbd image is assocatied with.  This
is in addition to the pool name already provided.

Rename the "poolid" field in struct rbd_device  to be "pool_id".

Update the documentation to reflect the addition of this new entry.
Signed-off-by: Alex Elder <elder@inktank.com>
Reviewed-by: Josh Durgin <josh.durgin@inktank.com>

Documentation/ABI/testing/sysfs-bus-rbd

@@ -35,8 +35,14 @@ name
 
 pool
 
-	The pool where this rbd image resides. The pool-name pair is unique
-	per rados system.
+	The name of the storage pool where this rbd image resides.
+	An rbd image name is unique within its pool.
+
+pool_id
+
+	The unique identifier for the rbd image's pool.  This is
+	a permanent attribute of the pool.  A pool's id will never
+	change.
 
 size
 

drivers/block/rbd.c

@@ -167,7 +167,7 @@ struct rbd_device {
 	int			obj_len;
 	char			obj_md_name[RBD_MAX_MD_NAME_LEN]; /* hdr nm. */
 	char			pool_name[RBD_MAX_POOL_NAME_LEN];
-	int			poolid;
+	int			pool_id;
 
 	struct ceph_osd_event   *watch_event;
 	struct ceph_osd_request *watch_request;
@@ -920,7 +920,7 @@ static int rbd_do_request(struct request *rq,
 	layout->fl_stripe_unit = cpu_to_le32(1 << RBD_MAX_OBJ_ORDER);
 	layout->fl_stripe_count = cpu_to_le32(1);
 	layout->fl_object_size = cpu_to_le32(1 << RBD_MAX_OBJ_ORDER);
-	layout->fl_pg_pool = cpu_to_le32(dev->poolid);
+	layout->fl_pg_pool = cpu_to_le32(dev->pool_id);
 	ceph_calc_raw_layout(osdc, layout, snapid, ofs, &len, &bno,
 				req, ops);
 
@@ -1643,7 +1643,7 @@ static int rbd_header_add_snap(struct rbd_device *dev,
 		return -EINVAL;
 
 	monc = &dev->rbd_client->client->monc;
-	ret = ceph_monc_create_snapid(monc, dev->poolid, &new_snapid);
+	ret = ceph_monc_create_snapid(monc, dev->pool_id, &new_snapid);
 	dout("created snapid=%lld\n", new_snapid);
 	if (ret < 0)
 		return ret;
@@ -1847,6 +1847,14 @@ static ssize_t rbd_pool_show(struct device *dev,
 	return sprintf(buf, "%s\n", rbd_dev->pool_name);
 }
 
+static ssize_t rbd_pool_id_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->pool_id);
+}
+
 static ssize_t rbd_name_show(struct device *dev,
 			     struct device_attribute *attr, char *buf)
 {
@@ -1887,6 +1895,7 @@ static DEVICE_ATTR(size, S_IRUGO, rbd_size_show, NULL);
 static DEVICE_ATTR(major, S_IRUGO, rbd_major_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);
 static DEVICE_ATTR(name, S_IRUGO, rbd_name_show, NULL);
 static DEVICE_ATTR(refresh, S_IWUSR, NULL, rbd_image_refresh);
 static DEVICE_ATTR(current_snap, S_IRUGO, rbd_snap_show, NULL);
@@ -1897,6 +1906,7 @@ static struct attribute *rbd_attrs[] = {
 	&dev_attr_major.attr,
 	&dev_attr_client_id.attr,
 	&dev_attr_pool.attr,
+	&dev_attr_pool_id.attr,
 	&dev_attr_name.attr,
 	&dev_attr_current_snap.attr,
 	&dev_attr_refresh.attr,
@@ -2430,7 +2440,7 @@ static ssize_t rbd_add(struct bus_type *bus,
 	rc = ceph_pg_poolid_by_name(osdc->osdmap, rbd_dev->pool_name);
 	if (rc < 0)
 		goto err_out_client;
-	rbd_dev->poolid = rc;
+	rbd_dev->pool_id = rc;
 
 	/* register our block device */
 	rc = register_blkdev(0, rbd_dev->name);