IB: Allow userspace to set node description

Expose a writable "node_desc" sysfs attribute for InfiniBand devices.
This allows userspace to update the node description with information
such as the node's hostname, so that IB network management software
can tie its view to the real world.
Signed-off-by: Michael S. Tsirkin <mst@mellanox.co.il>
Signed-off-by: Roland Dreier <rolandd@cisco.com>

drivers/infiniband/core/sysfs.c

@@ -628,14 +628,42 @@ static ssize_t show_node_guid(struct class_device *cdev, char *buf)
 		       be16_to_cpu(((__be16 *) &dev->node_guid)[3]));
 }
 
+static ssize_t show_node_desc(struct class_device *cdev, char *buf)
+{
+	struct ib_device *dev = container_of(cdev, struct ib_device, class_dev);
+
+	return sprintf(buf, "%.64s\n", dev->node_desc);
+}
+
+static ssize_t set_node_desc(struct class_device *cdev, const char *buf,
+			      size_t count)
+{
+	struct ib_device *dev = container_of(cdev, struct ib_device, class_dev);
+	struct ib_device_modify desc = {};
+	int ret;
+
+	if (!dev->modify_device)
+		return -EIO;
+
+	memcpy(desc.node_desc, buf, min_t(int, count, 64));
+	ret = ib_modify_device(dev, IB_DEVICE_MODIFY_NODE_DESC, &desc);
+	if (ret)
+		return ret;
+
+	return count;
+}
+
 static CLASS_DEVICE_ATTR(node_type, S_IRUGO, show_node_type, NULL);
 static CLASS_DEVICE_ATTR(sys_image_guid, S_IRUGO, show_sys_image_guid, NULL);
 static CLASS_DEVICE_ATTR(node_guid, S_IRUGO, show_node_guid, NULL);
+static CLASS_DEVICE_ATTR(node_desc, S_IRUGO | S_IWUSR, show_node_desc,
+			 set_node_desc);
 
 static struct class_device_attribute *ib_class_attributes[] = {
 	&class_device_attr_node_type,
 	&class_device_attr_sys_image_guid,
-	&class_device_attr_node_guid
+	&class_device_attr_node_guid,
+	&class_device_attr_node_desc
 };
 
 static struct class ib_class = {

include/rdma/ib_verbs.h

@@ -222,11 +222,13 @@ struct ib_port_attr {
 };
 
 enum ib_device_modify_flags {
-	IB_DEVICE_MODIFY_SYS_IMAGE_GUID	= 1
+	IB_DEVICE_MODIFY_SYS_IMAGE_GUID	= 1 << 0,
+	IB_DEVICE_MODIFY_NODE_DESC	= 1 << 1
 };
 
 struct ib_device_modify {
 	u64	sys_image_guid;
+	char	node_desc[64];
 };
 
 enum ib_port_modify_flags {
@@ -951,6 +953,7 @@ struct ib_device {
 	u64			     uverbs_cmd_mask;
 	int			     uverbs_abi_ver;
 
+	char			     node_desc[64];
 	__be64			     node_guid;
 	u8                           node_type;
 	u8                           phys_port_cnt;