IB/uverbs: Build the specs into a radix tree at runtime

This radix tree datastructure is intended to replace the 'hash' structure
used today for parsing ioctl methods during system calls. This first
commit introduces the structure and builds it from the existing .rodata
descriptions.

The so-called hash arrangement is actually a 5 level open coded radix tree.
This new version uses a 3 level radix tree built using the radix tree
library.

Overall this is much less code and much easier to build as the radix tree
API allows for dynamic modification during the building. There is a small
memory penalty to pay for this, but since the radix tree is allocated on
a per device basis, a few kb of RAM seems immaterial considering the
gained simplicity.

The radix tree is similar to the existing tree, but also has a 'attr_bkey'
concept, which is a small value'd index for each method attribute. This is
used to simplify and improve performance of everything in the next
patches.
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>
Reviewed-by: Leon Romanovsky <leonro@mellanox.com>
Reviewed-by: Michael J. Ruhl <michael.j.ruhl@intel.com>

drivers/infiniband/core/Makefile

@@ -37,4 +37,5 @@ ib_uverbs-y :=			uverbs_main.o uverbs_cmd.o uverbs_marshall.o \
 				rdma_core.o uverbs_std_types.o uverbs_ioctl.o \
 				uverbs_ioctl_merge.o uverbs_std_types_cq.o \
 				uverbs_std_types_flow_action.o uverbs_std_types_dm.o \
-				uverbs_std_types_mr.o uverbs_std_types_counters.o
+				uverbs_std_types_mr.o uverbs_std_types_counters.o \
+				uverbs_uapi.o

drivers/infiniband/core/rdma_core.h

@@ -43,6 +43,8 @@
 #include <rdma/ib_verbs.h>
 #include <linux/mutex.h>
 
+struct ib_uverbs_device;
+
 int uverbs_ns_idx(u16 *id, unsigned int ns_count);
 const struct uverbs_object_spec *uverbs_get_object(struct ib_uverbs_file *ufile,
 						   uint16_t object);
@@ -113,4 +115,52 @@ int uverbs_finalize_object(struct ib_uobject *uobj,
 void setup_ufile_idr_uobject(struct ib_uverbs_file *ufile);
 void release_ufile_idr_uobject(struct ib_uverbs_file *ufile);
 
+/*
+ * This is the runtime description of the uverbs API, used by the syscall
+ * machinery to validate and dispatch calls.
+ */
+
+/*
+ * Depending on ID the slot pointer in the radix tree points at one of these
+ * structs.
+ */
+struct uverbs_api_object {
+	const struct uverbs_obj_type *type_attrs;
+	const struct uverbs_obj_type_class *type_class;
+};
+
+struct uverbs_api_ioctl_method {
+	int (__rcu *handler)(struct ib_uverbs_file *ufile,
+			     struct uverbs_attr_bundle *ctx);
+	DECLARE_BITMAP(attr_mandatory, UVERBS_API_ATTR_BKEY_LEN);
+	u8 driver_method:1;
+	u8 key_bitmap_len;
+	u8 destroy_bkey;
+};
+
+struct uverbs_api_attr {
+	struct uverbs_attr_spec spec;
+};
+
+struct uverbs_api_object;
+struct uverbs_api {
+	/* radix tree contains struct uverbs_api_* pointers */
+	struct radix_tree_root radix;
+	enum rdma_driver_id driver_id;
+};
+
+static inline const struct uverbs_api_object *
+uapi_get_object(struct uverbs_api *uapi, u16 object_id)
+{
+	return radix_tree_lookup(&uapi->radix, uapi_key_obj(object_id));
+}
+
+char *uapi_key_format(char *S, unsigned int key);
+struct uverbs_api *uverbs_alloc_api(
+	const struct uverbs_object_tree_def *const *driver_specs,
+	enum rdma_driver_id driver_id);
+void uverbs_disassociate_api_pre(struct ib_uverbs_device *uverbs_dev);
+void uverbs_disassociate_api(struct uverbs_api *uapi);
+void uverbs_destroy_api(struct uverbs_api *uapi);
+
 #endif /* RDMA_CORE_H */

drivers/infiniband/core/uverbs.h

@@ -112,6 +112,7 @@ struct ib_uverbs_device {
 	struct list_head			uverbs_file_list;
 	struct list_head			uverbs_events_file_list;
 	struct uverbs_root_spec			*specs_root;
+	struct uverbs_api			*uapi;
 };
 
 struct ib_uverbs_event_queue {

drivers/infiniband/core/uverbs_main.c

@@ -174,6 +174,7 @@ static void ib_uverbs_release_dev(struct kobject *kobj)
 	struct ib_uverbs_device *dev =
 		container_of(kobj, struct ib_uverbs_device, kobj);
 
+	uverbs_destroy_api(dev->uapi);
 	cleanup_srcu_struct(&dev->disassociate_srcu);
 	uverbs_free_spec_tree(dev->specs_root);
 	kfree(dev);
@@ -1000,6 +1001,7 @@ static int ib_uverbs_create_uapi(struct ib_device *device,
 	const struct uverbs_object_tree_def **specs;
 	struct uverbs_root_spec *specs_root;
 	unsigned int num_specs = 1;
+	struct uverbs_api *uapi;
 	unsigned int i;
 
 	if (device->driver_specs)
@@ -1020,7 +1022,14 @@ static int ib_uverbs_create_uapi(struct ib_device *device,
 	if (IS_ERR(specs_root))
 		return PTR_ERR(specs_root);
 
+	uapi = uverbs_alloc_api(device->driver_specs, device->driver_id);
+	if (IS_ERR(uapi)) {
+		uverbs_free_spec_tree(specs_root);
+		return PTR_ERR(uapi);
+	}
+
 	uverbs_dev->specs_root = specs_root;
+	uverbs_dev->uapi = uapi;
 	return 0;
 }
 
@@ -1115,7 +1124,7 @@ static void ib_uverbs_free_hw_resources(struct ib_uverbs_device *uverbs_dev,
 	struct ib_event event;
 
 	/* Pending running commands to terminate */
-	synchronize_srcu(&uverbs_dev->disassociate_srcu);
+	uverbs_disassociate_api_pre(uverbs_dev);
 	event.event = IB_EVENT_DEVICE_FATAL;
 	event.element.port_num = 0;
 	event.device = ib_dev;
@@ -1161,6 +1170,8 @@ static void ib_uverbs_free_hw_resources(struct ib_uverbs_device *uverbs_dev,
 		kill_fasync(&event_file->ev_queue.async_queue, SIGIO, POLL_IN);
 	}
 	mutex_unlock(&uverbs_dev->lists_mutex);
+
+	uverbs_disassociate_api(uverbs_dev->uapi);
 }
 
 static void ib_uverbs_remove_one(struct ib_device *device, void *client_data)
@@ -1188,7 +1199,6 @@ static void ib_uverbs_remove_one(struct ib_device *device, void *client_data)
 		 * cdev was deleted, however active clients can still issue
 		 * commands and close their open files.
 		 */
-		rcu_assign_pointer(uverbs_dev->ib_dev, NULL);
 		ib_uverbs_free_hw_resources(uverbs_dev, device);
 		wait_clients = 0;
 	}

drivers/infiniband/core/uverbs_uapi.c

+// SPDX-License-Identifier: GPL-2.0 OR Linux-OpenIB
+/*
+ * Copyright (c) 2017, Mellanox Technologies inc.  All rights reserved.
+ */
+#include <rdma/uverbs_ioctl.h>
+#include <rdma/rdma_user_ioctl.h>
+#include <linux/bitops.h>
+#include "rdma_core.h"
+#include "uverbs.h"
+
+static void *uapi_add_elm(struct uverbs_api *uapi, u32 key, size_t alloc_size)
+{
+	void *elm;
+	int rc;
+
+	if (key == UVERBS_API_KEY_ERR)
+		return ERR_PTR(-EOVERFLOW);
+
+	elm = kzalloc(alloc_size, GFP_KERNEL);
+	rc = radix_tree_insert(&uapi->radix, key, elm);
+	if (rc) {
+		kfree(elm);
+		return ERR_PTR(rc);
+	}
+
+	return elm;
+}
+
+static int uapi_merge_method(struct uverbs_api *uapi,
+			     struct uverbs_api_object *obj_elm, u32 obj_key,
+			     const struct uverbs_method_def *method,
+			     bool is_driver)
+{
+	u32 method_key = obj_key | uapi_key_ioctl_method(method->id);
+	struct uverbs_api_ioctl_method *method_elm;
+	unsigned int i;
+
+	if (!method->attrs)
+		return 0;
+
+	method_elm = uapi_add_elm(uapi, method_key, sizeof(*method_elm));
+	if (IS_ERR(method_elm)) {
+		if (method_elm != ERR_PTR(-EEXIST))
+			return PTR_ERR(method_elm);
+
+		/*
+		 * This occurs when a driver uses ADD_UVERBS_ATTRIBUTES_SIMPLE
+		 */
+		if (WARN_ON(method->handler))
+			return -EINVAL;
+		method_elm = radix_tree_lookup(&uapi->radix, method_key);
+		if (WARN_ON(!method_elm))
+			return -EINVAL;
+	} else {
+		WARN_ON(!method->handler);
+		rcu_assign_pointer(method_elm->handler, method->handler);
+		if (method->handler != uverbs_destroy_def_handler)
+			method_elm->driver_method = is_driver;
+	}
+
+	for (i = 0; i != method->num_attrs; i++) {
+		const struct uverbs_attr_def *attr = (*method->attrs)[i];
+		struct uverbs_api_attr *attr_slot;
+
+		if (!attr)
+			continue;
+
+		/*
+		 * ENUM_IN contains the 'ids' pointer to the driver's .rodata,
+		 * so if it is specified by a driver then it always makes this
+		 * into a driver method.
+		 */
+		if (attr->attr.type == UVERBS_ATTR_TYPE_ENUM_IN)
+			method_elm->driver_method |= is_driver;
+
+		attr_slot =
+			uapi_add_elm(uapi, method_key | uapi_key_attr(attr->id),
+				     sizeof(*attr_slot));
+		/* Attributes are not allowed to be modified by drivers */
+		if (IS_ERR(attr_slot))
+			return PTR_ERR(attr_slot);
+
+		attr_slot->spec = attr->attr;
+	}
+
+	return 0;
+}
+
+static int uapi_merge_tree(struct uverbs_api *uapi,
+			   const struct uverbs_object_tree_def *tree,
+			   bool is_driver)
+{
+	unsigned int i, j;
+	int rc;
+
+	if (!tree->objects)
+		return 0;
+
+	for (i = 0; i != tree->num_objects; i++) {
+		const struct uverbs_object_def *obj = (*tree->objects)[i];
+		struct uverbs_api_object *obj_elm;
+		u32 obj_key;
+
+		if (!obj)
+			continue;
+
+		obj_key = uapi_key_obj(obj->id);
+		obj_elm = uapi_add_elm(uapi, obj_key, sizeof(*obj_elm));
+		if (IS_ERR(obj_elm)) {
+			if (obj_elm != ERR_PTR(-EEXIST))
+				return PTR_ERR(obj_elm);
+
+			/* This occurs when a driver uses ADD_UVERBS_METHODS */
+			if (WARN_ON(obj->type_attrs))
+				return -EINVAL;
+			obj_elm = radix_tree_lookup(&uapi->radix, obj_key);
+			if (WARN_ON(!obj_elm))
+				return -EINVAL;
+		} else {
+			obj_elm->type_attrs = obj->type_attrs;
+			if (obj->type_attrs) {
+				obj_elm->type_class =
+					obj->type_attrs->type_class;
+				/*
+				 * Today drivers are only permitted to use
+				 * idr_class types. They cannot use FD types
+				 * because we currently have no way to revoke
+				 * the fops pointer after device
+				 * disassociation.
+				 */
+				if (WARN_ON(is_driver &&
+					    obj->type_attrs->type_class !=
+						    &uverbs_idr_class))
+					return -EINVAL;
+			}
+		}
+
+		if (!obj->methods)
+			continue;
+
+		for (j = 0; j != obj->num_methods; j++) {
+			const struct uverbs_method_def *method =
+				(*obj->methods)[j];
+			if (!method)
+				continue;
+
+			rc = uapi_merge_method(uapi, obj_elm, obj_key, method,
+					       is_driver);
+			if (rc)
+				return rc;
+		}
+	}
+
+	return 0;
+}
+
+static int
+uapi_finalize_ioctl_method(struct uverbs_api *uapi,
+			   struct uverbs_api_ioctl_method *method_elm,
+			   u32 method_key)
+{
+	struct radix_tree_iter iter;
+	unsigned int max_bkey = 0;
+	bool single_uobj = false;
+	void __rcu **slot;
+
+	method_elm->destroy_bkey = UVERBS_API_ATTR_BKEY_LEN;
+	radix_tree_for_each_slot (slot, &uapi->radix, &iter,
+				  uapi_key_attrs_start(method_key)) {
+		struct uverbs_api_attr *elm =
+			rcu_dereference_protected(*slot, true);
+		u32 attr_key = iter.index & UVERBS_API_ATTR_KEY_MASK;
+		u32 attr_bkey = uapi_bkey_attr(attr_key);
+		u8 type = elm->spec.type;
+
+		if (uapi_key_attr_to_method(iter.index) !=
+		    uapi_key_attr_to_method(method_key))
+			break;
+
+		if (elm->spec.mandatory)
+			__set_bit(attr_bkey, method_elm->attr_mandatory);
+
+		if (type == UVERBS_ATTR_TYPE_IDR ||
+		    type == UVERBS_ATTR_TYPE_FD) {
+			u8 access = elm->spec.u.obj.access;
+
+			/*
+			 * Verbs specs may only have one NEW/DESTROY, we don't
+			 * have the infrastructure to abort multiple NEW's or
+			 * cope with multiple DESTROY failure.
+			 */
+			if (access == UVERBS_ACCESS_NEW ||
+			    access == UVERBS_ACCESS_DESTROY) {
+				if (WARN_ON(single_uobj))
+					return -EINVAL;
+
+				single_uobj = true;
+				if (WARN_ON(!elm->spec.mandatory))
+					return -EINVAL;
+			}
+
+			if (access == UVERBS_ACCESS_DESTROY)
+				method_elm->destroy_bkey = attr_bkey;
+		}
+
+		max_bkey = max(max_bkey, attr_bkey);
+	}
+
+	method_elm->key_bitmap_len = max_bkey + 1;
+	WARN_ON(method_elm->key_bitmap_len > UVERBS_API_ATTR_BKEY_LEN);
+
+	return 0;
+}
+
+static int uapi_finalize(struct uverbs_api *uapi)
+{
+	struct radix_tree_iter iter;
+	void __rcu **slot;
+	int rc;
+
+	radix_tree_for_each_slot (slot, &uapi->radix, &iter, 0) {
+		struct uverbs_api_ioctl_method *method_elm =
+			rcu_dereference_protected(*slot, true);
+
+		if (uapi_key_is_ioctl_method(iter.index)) {
+			rc = uapi_finalize_ioctl_method(uapi, method_elm,
+							iter.index);
+			if (rc)
+				return rc;
+		}
+	}
+
+	return 0;
+}
+
+void uverbs_destroy_api(struct uverbs_api *uapi)
+{
+	struct radix_tree_iter iter;
+	void __rcu **slot;
+
+	if (!uapi)
+		return;
+
+	radix_tree_for_each_slot (slot, &uapi->radix, &iter, 0) {
+		kfree(rcu_dereference_protected(*slot, true));
+		radix_tree_iter_delete(&uapi->radix, &iter, slot);
+	}
+}
+
+struct uverbs_api *uverbs_alloc_api(
+	const struct uverbs_object_tree_def *const *driver_specs,
+	enum rdma_driver_id driver_id)
+{
+	struct uverbs_api *uapi;
+	int rc;
+
+	uapi = kzalloc(sizeof(*uapi), GFP_KERNEL);
+	if (!uapi)
+		return ERR_PTR(-ENOMEM);
+
+	INIT_RADIX_TREE(&uapi->radix, GFP_KERNEL);
+	uapi->driver_id = driver_id;
+
+	rc = uapi_merge_tree(uapi, uverbs_default_get_objects(), false);
+	if (rc)
+		goto err;
+
+	for (; driver_specs && *driver_specs; driver_specs++) {
+		rc = uapi_merge_tree(uapi, *driver_specs, true);
+		if (rc)
+			goto err;
+	}
+
+	rc = uapi_finalize(uapi);
+	if (rc)
+		goto err;
+
+	return uapi;
+err:
+	if (rc != -ENOMEM)
+		pr_err("Setup of uverbs_api failed, kernel parsing tree description is not valid (%d)??\n",
+		       rc);
+
+	uverbs_destroy_api(uapi);
+	return ERR_PTR(rc);
+}
+
+/*
+ * The pre version is done before destroying the HW objects, it only blocks
+ * off method access. All methods that require the ib_dev or the module data
+ * must test one of these assignments prior to continuing.
+ */
+void uverbs_disassociate_api_pre(struct ib_uverbs_device *uverbs_dev)
+{
+	struct uverbs_api *uapi = uverbs_dev->uapi;
+	struct radix_tree_iter iter;
+	void __rcu **slot;
+
+	rcu_assign_pointer(uverbs_dev->ib_dev, NULL);
+
+	radix_tree_for_each_slot (slot, &uapi->radix, &iter, 0) {
+		if (uapi_key_is_ioctl_method(iter.index)) {
+			struct uverbs_api_ioctl_method *method_elm =
+				rcu_dereference_protected(*slot, true);
+
+			if (method_elm->driver_method)
+				rcu_assign_pointer(method_elm->handler, NULL);
+		}
+	}
+
+	synchronize_srcu(&uverbs_dev->disassociate_srcu);
+}
+
+/*
+ * Called when a driver disassociates from the ib_uverbs_device. The
+ * assumption is that the driver module will unload after. Replace everything
+ * related to the driver with NULL as a safety measure.
+ */
+void uverbs_disassociate_api(struct uverbs_api *uapi)
+{
+	struct radix_tree_iter iter;
+	void __rcu **slot;
+
+	radix_tree_for_each_slot (slot, &uapi->radix, &iter, 0) {
+		if (uapi_key_is_object(iter.index)) {
+			struct uverbs_api_object *object_elm =
+				rcu_dereference_protected(*slot, true);
+
+			/*
+			 * Some type_attrs are in the driver module. We don't
+			 * bother to keep track of which since there should be
+			 * no use of this after disassociate.
+			 */
+			object_elm->type_attrs = NULL;
+		} else if (uapi_key_is_attr(iter.index)) {
+			struct uverbs_api_attr *elm =
+				rcu_dereference_protected(*slot, true);
+
+			if (elm->spec.type == UVERBS_ATTR_TYPE_ENUM_IN)
+				elm->spec.u2.enum_def.ids = NULL;
+		}
+	}
+}

include/rdma/uverbs_ioctl.h

@@ -154,6 +154,143 @@ struct uverbs_root_spec {
 	struct uverbs_object_spec_hash		*object_buckets[0];
 };
 
+/*
+ * Information about the API is loaded into a radix tree. For IOCTL we start
+ * with a tuple of:
+ *  object_id, attr_id, method_id
+ *
+ * Which is a 48 bit value, with most of the bits guaranteed to be zero. Based
+ * on the current kernel support this is compressed into 16 bit key for the
+ * radix tree. Since this compression is entirely internal to the kernel the
+ * below limits can be revised if the kernel gains additional data.
+ *
+ * With 64 leafs per node this is a 3 level radix tree.
+ *
+ * The tree encodes multiple types, and uses a scheme where OBJ_ID,0,0 returns
+ * the object slot, and OBJ_ID,METH_ID,0 and returns the method slot.
+ */
+enum uapi_radix_data {
+	UVERBS_API_NS_FLAG = 1U << UVERBS_ID_NS_SHIFT,
+
+	UVERBS_API_ATTR_KEY_BITS = 6,
+	UVERBS_API_ATTR_KEY_MASK = GENMASK(UVERBS_API_ATTR_KEY_BITS - 1, 0),
+	UVERBS_API_ATTR_BKEY_LEN = (1 << UVERBS_API_ATTR_KEY_BITS) - 1,
+
+	UVERBS_API_METHOD_KEY_BITS = 5,
+	UVERBS_API_METHOD_KEY_SHIFT = UVERBS_API_ATTR_KEY_BITS,
+	UVERBS_API_METHOD_KEY_NUM_CORE = 24,
+	UVERBS_API_METHOD_KEY_NUM_DRIVER = (1 << UVERBS_API_METHOD_KEY_BITS) -
+					   UVERBS_API_METHOD_KEY_NUM_CORE,
+	UVERBS_API_METHOD_KEY_MASK = GENMASK(
+		UVERBS_API_METHOD_KEY_BITS + UVERBS_API_METHOD_KEY_SHIFT - 1,
+		UVERBS_API_METHOD_KEY_SHIFT),
+
+	UVERBS_API_OBJ_KEY_BITS = 5,
+	UVERBS_API_OBJ_KEY_SHIFT =
+		UVERBS_API_METHOD_KEY_BITS + UVERBS_API_METHOD_KEY_SHIFT,
+	UVERBS_API_OBJ_KEY_NUM_CORE = 24,
+	UVERBS_API_OBJ_KEY_NUM_DRIVER =
+		(1 << UVERBS_API_OBJ_KEY_BITS) - UVERBS_API_OBJ_KEY_NUM_CORE,
+	UVERBS_API_OBJ_KEY_MASK = GENMASK(31, UVERBS_API_OBJ_KEY_SHIFT),
+
+	/* This id guaranteed to not exist in the radix tree */
+	UVERBS_API_KEY_ERR = 0xFFFFFFFF,
+};
+
+static inline __attribute_const__ u32 uapi_key_obj(u32 id)
+{
+	if (id & UVERBS_API_NS_FLAG) {
+		id &= ~UVERBS_API_NS_FLAG;
+		if (id >= UVERBS_API_OBJ_KEY_NUM_DRIVER)
+			return UVERBS_API_KEY_ERR;
+		id = id + UVERBS_API_OBJ_KEY_NUM_CORE;
+	} else {
+		if (id >= UVERBS_API_OBJ_KEY_NUM_CORE)
+			return UVERBS_API_KEY_ERR;
+	}
+
+	return id << UVERBS_API_OBJ_KEY_SHIFT;
+}
+
+static inline __attribute_const__ bool uapi_key_is_object(u32 key)
+{
+	return (key & ~UVERBS_API_OBJ_KEY_MASK) == 0;
+}
+
+static inline __attribute_const__ u32 uapi_key_ioctl_method(u32 id)
+{
+	if (id & UVERBS_API_NS_FLAG) {
+		id &= ~UVERBS_API_NS_FLAG;
+		if (id >= UVERBS_API_METHOD_KEY_NUM_DRIVER)
+			return UVERBS_API_KEY_ERR;
+		id = id + UVERBS_API_METHOD_KEY_NUM_CORE;
+	} else {
+		id++;
+		if (id >= UVERBS_API_METHOD_KEY_NUM_CORE)
+			return UVERBS_API_KEY_ERR;
+	}
+
+	return id << UVERBS_API_METHOD_KEY_SHIFT;
+}
+
+static inline __attribute_const__ u32 uapi_key_attr_to_method(u32 attr_key)
+{
+	return attr_key &
+	       (UVERBS_API_OBJ_KEY_MASK | UVERBS_API_METHOD_KEY_MASK);
+}
+
+static inline __attribute_const__ bool uapi_key_is_ioctl_method(u32 key)
+{
+	return (key & UVERBS_API_METHOD_KEY_MASK) != 0 &&
+	       (key & UVERBS_API_ATTR_KEY_MASK) == 0;
+}
+
+static inline __attribute_const__ u32 uapi_key_attrs_start(u32 ioctl_method_key)
+{
+	/* 0 is the method slot itself */
+	return ioctl_method_key + 1;
+}
+
+static inline __attribute_const__ u32 uapi_key_attr(u32 id)
+{
+	/*
+	 * The attr is designed to fit in the typical single radix tree node
+	 * of 64 entries. Since allmost all methods have driver attributes we
+	 * organize things so that the driver and core attributes interleave to
+	 * reduce the length of the attributes array in typical cases.
+	 */
+	if (id & UVERBS_API_NS_FLAG) {
+		id &= ~UVERBS_API_NS_FLAG;
+		id++;
+		if (id >= 1 << (UVERBS_API_ATTR_KEY_BITS - 1))
+			return UVERBS_API_KEY_ERR;
+		id = (id << 1) | 0;
+	} else {
+		if (id >= 1 << (UVERBS_API_ATTR_KEY_BITS - 1))
+			return UVERBS_API_KEY_ERR;
+		id = (id << 1) | 1;
+	}
+
+	return id;
+}
+
+static inline __attribute_const__ bool uapi_key_is_attr(u32 key)
+{
+	return (key & UVERBS_API_METHOD_KEY_MASK) != 0 &&
+	       (key & UVERBS_API_ATTR_KEY_MASK) != 0;
+}
+
+/*
+ * This returns a value in the range [0 to UVERBS_API_ATTR_BKEY_LEN),
+ * basically it undoes the reservation of 0 in the ID numbering. attr_key
+ * must already be masked with UVERBS_API_ATTR_KEY_MASK, or be the output of
+ * uapi_key_attr().
+ */
+static inline __attribute_const__ u32 uapi_bkey_attr(u32 attr_key)
+{
+	return attr_key - 1;
+}
+
 /*
  * =======================================
  *	Verbs definitions