rbd: get and check striping parameters

If an rbd format 2 image indicates it supports the STRIPINGV2
feature we need to find out its stripe unit and stripe count in
order to know whether we can use it.  We don't yet support fancy
striping fully, but if the default parameters are used the behavior
is indistinguishible from non-fancy striping.

This is necessary because some images require the STRIPINGV2 feature
even if they use the default parameters.  (Which is to say the feature
bit was erroneously set even if the feature was not used.)

This resolves:
    http://tracker.ceph.com/issues/4709Signed-off-by: Alex Elder <elder@inktank.com>
Reviewed-by: Josh Durgin <josh.durgin@inktank.com>

drivers/block/rbd.c

@@ -317,6 +317,9 @@ struct rbd_device {
 	u64			parent_overlap;
 	struct rbd_device	*parent;
 
+	u64			stripe_unit;
+	u64			stripe_count;
+
 	/* protects updating the header */
 	struct rw_semaphore     header_rwsem;
 
@@ -3749,6 +3752,56 @@ static int rbd_dev_v2_parent_info(struct rbd_device *rbd_dev)
 	return ret;
 }
 
+static int rbd_dev_v2_striping_info(struct rbd_device *rbd_dev)
+{
+	struct {
+		__le64 stripe_unit;
+		__le64 stripe_count;
+	} __attribute__ ((packed)) striping_info_buf = { 0 };
+	size_t size = sizeof (striping_info_buf);
+	void *p;
+	u64 obj_size;
+	u64 stripe_unit;
+	u64 stripe_count;
+	int ret;
+
+	ret = rbd_obj_method_sync(rbd_dev, rbd_dev->header_name,
+				"rbd", "get_stripe_unit_count", NULL, 0,
+				(char *)&striping_info_buf, size, NULL);
+	dout("%s: rbd_obj_method_sync returned %d\n", __func__, ret);
+	if (ret < 0)
+		return ret;
+	if (ret < size)
+		return -ERANGE;
+
+	/*
+	 * We don't actually support the "fancy striping" feature
+	 * (STRIPINGV2) yet, but if the striping sizes are the
+	 * defaults the behavior is the same as before.  So find
+	 * out, and only fail if the image has non-default values.
+	 */
+	ret = -EINVAL;
+	obj_size = (u64)1 << rbd_dev->header.obj_order;
+	p = &striping_info_buf;
+	stripe_unit = ceph_decode_64(&p);
+	if (stripe_unit != obj_size) {
+		rbd_warn(rbd_dev, "unsupported stripe unit "
+				"(got %llu want %llu)",
+				stripe_unit, obj_size);
+		return -EINVAL;
+	}
+	stripe_count = ceph_decode_64(&p);
+	if (stripe_count != 1) {
+		rbd_warn(rbd_dev, "unsupported stripe count "
+				"(got %llu want 1)", stripe_count);
+		return -EINVAL;
+	}
+	rbd_dev->stripe_unit = stripe_unit;
+	rbd_dev->stripe_count = stripe_count;
+
+	return 0;
+}
+
 static char *rbd_dev_image_name(struct rbd_device *rbd_dev)
 {
 	size_t image_id_size;
@@ -4673,6 +4726,14 @@ static int rbd_dev_v2_probe(struct rbd_device *rbd_dev)
 			goto out_err;
 	}
 
+	/* If the image supports fancy striping, get its parameters */
+
+	if (rbd_dev->header.features & RBD_FEATURE_STRIPINGV2) {
+		ret = rbd_dev_v2_striping_info(rbd_dev);
+		if (ret < 0)
+			goto out_err;
+	}
+
 	/* crypto and compression type aren't (yet) supported for v2 images */
 
 	rbd_dev->header.crypt_type = 0;