RDMA/core: Expose the ib port sysfs attribute machinery

Other things outside the core code are creating attributes against the
port. This patch exposes the basic machinery to do this.

The ib_port_attribute type allows creating groups of attributes attatched
to the port and comes with the usual machinery to do this.

Link: https://lore.kernel.org/r/5c4aeae57f6fa7c59a1d6d1c5506069516ae9bbf.1623427137.git.leonro@nvidia.comSigned-off-by: Leon Romanovsky <leonro@nvidia.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>

include/rdma/ib_sysfs.h

+/* SPDX-License-Identifier: GPL-2.0 OR BSD-3-Clause */
+/*
+ * Copyright (c) 2021 Mellanox Technologies Ltd.  All rights reserved.
+ */
+#ifndef DEF_RDMA_IB_SYSFS_H
+#define DEF_RDMA_IB_SYSFS_H
+
+#include <linux/sysfs.h>
+
+struct ib_device;
+
+struct ib_port_attribute {
+	struct attribute attr;
+	ssize_t (*show)(struct ib_device *ibdev, u32 port_num,
+			struct ib_port_attribute *attr, char *buf);
+	ssize_t (*store)(struct ib_device *ibdev, u32 port_num,
+			 struct ib_port_attribute *attr, const char *buf,
+			 size_t count);
+};
+
+#define IB_PORT_ATTR_RW(_name)                                                 \
+	struct ib_port_attribute ib_port_attr_##_name = __ATTR_RW(_name)
+
+#define IB_PORT_ATTR_ADMIN_RW(_name)                                           \
+	struct ib_port_attribute ib_port_attr_##_name =                        \
+		__ATTR_RW_MODE(_name, 0600)
+
+#define IB_PORT_ATTR_RO(_name)                                                 \
+	struct ib_port_attribute ib_port_attr_##_name = __ATTR_RO(_name)
+
+#define IB_PORT_ATTR_WO(_name)                                                 \
+	struct ib_port_attribute ib_port_attr_##_name = __ATTR_WO(_name)
+
+int ib_port_sysfs_create_groups(struct ib_device *ibdev, u32 port_num,
+				const struct attribute_group **groups);
+void ib_port_sysfs_remove_groups(struct ib_device *ibdev, u32 port_num,
+				 const struct attribute_group **groups);
+struct ib_device *ib_port_sysfs_get_ibdev_kobj(struct kobject *kobj,
+					       u32 *port_num);
+
+#endif