Linux kernel mirror (for testing)
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1// SPDX-License-Identifier: GPL-2.0-only
2/*
3 * Copyright (c) 2025 Greg Kroah-Hartman <gregkh@linuxfoundation.org>
4 * Copyright (c) 2025 The Linux Foundation
5 *
6 * A "simple" faux bus that allows devices to be created and added
7 * automatically to it. This is to be used whenever you need to create a
8 * device that is not associated with any "real" system resources, and do
9 * not want to have to deal with a bus/driver binding logic. It is
10 * intended to be very simple, with only a create and a destroy function
11 * available.
12 */
13#include <linux/err.h>
14#include <linux/init.h>
15#include <linux/slab.h>
16#include <linux/string.h>
17#include <linux/container_of.h>
18#include <linux/device/faux.h>
19#include "base.h"
20
21/*
22 * Internal wrapper structure so we can hold a pointer to the
23 * faux_device_ops for this device.
24 */
25struct faux_object {
26 struct faux_device faux_dev;
27 const struct faux_device_ops *faux_ops;
28 const struct attribute_group **groups;
29};
30#define to_faux_object(dev) container_of_const(dev, struct faux_object, faux_dev.dev)
31
32static struct device *faux_bus_root;
33
34static int faux_match(struct device *dev, const struct device_driver *drv)
35{
36 /* Match always succeeds, we only have one driver */
37 return 1;
38}
39
40static int faux_probe(struct device *dev)
41{
42 struct faux_object *faux_obj = to_faux_object(dev);
43 struct faux_device *faux_dev = &faux_obj->faux_dev;
44 const struct faux_device_ops *faux_ops = faux_obj->faux_ops;
45 int ret;
46
47 if (faux_ops && faux_ops->probe) {
48 ret = faux_ops->probe(faux_dev);
49 if (ret)
50 return ret;
51 }
52
53 /*
54 * Add groups after the probe succeeds to ensure resources are
55 * initialized correctly
56 */
57 ret = device_add_groups(dev, faux_obj->groups);
58 if (ret && faux_ops && faux_ops->remove)
59 faux_ops->remove(faux_dev);
60
61 return ret;
62}
63
64static void faux_remove(struct device *dev)
65{
66 struct faux_object *faux_obj = to_faux_object(dev);
67 struct faux_device *faux_dev = &faux_obj->faux_dev;
68 const struct faux_device_ops *faux_ops = faux_obj->faux_ops;
69
70 device_remove_groups(dev, faux_obj->groups);
71
72 if (faux_ops && faux_ops->remove)
73 faux_ops->remove(faux_dev);
74}
75
76static const struct bus_type faux_bus_type = {
77 .name = "faux",
78 .match = faux_match,
79 .probe = faux_probe,
80 .remove = faux_remove,
81};
82
83static struct device_driver faux_driver = {
84 .name = "faux_driver",
85 .bus = &faux_bus_type,
86 .probe_type = PROBE_FORCE_SYNCHRONOUS,
87 .suppress_bind_attrs = true,
88};
89
90static void faux_device_release(struct device *dev)
91{
92 struct faux_object *faux_obj = to_faux_object(dev);
93
94 kfree(faux_obj);
95}
96
97/**
98 * faux_device_create_with_groups - Create and register with the driver
99 * core a faux device and populate the device with an initial
100 * set of sysfs attributes.
101 * @name: The name of the device we are adding, must be unique for
102 * all faux devices.
103 * @parent: Pointer to a potential parent struct device. If set to
104 * NULL, the device will be created in the "root" of the faux
105 * device tree in sysfs.
106 * @faux_ops: struct faux_device_ops that the new device will call back
107 * into, can be NULL.
108 * @groups: The set of sysfs attributes that will be created for this
109 * device when it is registered with the driver core.
110 *
111 * Create a new faux device and register it in the driver core properly.
112 * If present, callbacks in @faux_ops will be called with the device that
113 * for the caller to do something with at the proper time given the
114 * device's lifecycle.
115 *
116 * Note, when this function is called, the functions specified in struct
117 * faux_ops can be called before the function returns, so be prepared for
118 * everything to be properly initialized before that point in time. If the
119 * probe callback (if one is present) does NOT succeed, the creation of the
120 * device will fail and NULL will be returned.
121 *
122 * Return:
123 * * NULL if an error happened with creating the device
124 * * pointer to a valid struct faux_device that is registered with sysfs
125 */
126struct faux_device *faux_device_create_with_groups(const char *name,
127 struct device *parent,
128 const struct faux_device_ops *faux_ops,
129 const struct attribute_group **groups)
130{
131 struct faux_object *faux_obj;
132 struct faux_device *faux_dev;
133 struct device *dev;
134 int ret;
135
136 faux_obj = kzalloc_obj(*faux_obj);
137 if (!faux_obj)
138 return NULL;
139
140 /* Save off the callbacks and groups so we can use them in the future */
141 faux_obj->faux_ops = faux_ops;
142 faux_obj->groups = groups;
143
144 /* Initialize the device portion and register it with the driver core */
145 faux_dev = &faux_obj->faux_dev;
146 dev = &faux_dev->dev;
147
148 device_initialize(dev);
149 dev->release = faux_device_release;
150 if (parent)
151 dev->parent = parent;
152 else
153 dev->parent = faux_bus_root;
154 dev->bus = &faux_bus_type;
155 dev_set_name(dev, "%s", name);
156 device_set_pm_not_required(dev);
157
158 ret = device_add(dev);
159 if (ret) {
160 pr_err("%s: device_add for faux device '%s' failed with %d\n",
161 __func__, name, ret);
162 put_device(dev);
163 return NULL;
164 }
165
166 /*
167 * Verify that we did bind the driver to the device (i.e. probe worked),
168 * if not, let's fail the creation as trying to guess if probe was
169 * successful is almost impossible to determine by the caller.
170 */
171 if (!dev->driver) {
172 dev_dbg(dev, "probe did not succeed, tearing down the device\n");
173 faux_device_destroy(faux_dev);
174 faux_dev = NULL;
175 }
176
177 return faux_dev;
178}
179EXPORT_SYMBOL_GPL(faux_device_create_with_groups);
180
181/**
182 * faux_device_create - create and register with the driver core a faux device
183 * @name: The name of the device we are adding, must be unique for all
184 * faux devices.
185 * @parent: Pointer to a potential parent struct device. If set to
186 * NULL, the device will be created in the "root" of the faux
187 * device tree in sysfs.
188 * @faux_ops: struct faux_device_ops that the new device will call back
189 * into, can be NULL.
190 *
191 * Create a new faux device and register it in the driver core properly.
192 * If present, callbacks in @faux_ops will be called with the device that
193 * for the caller to do something with at the proper time given the
194 * device's lifecycle.
195 *
196 * Note, when this function is called, the functions specified in struct
197 * faux_ops can be called before the function returns, so be prepared for
198 * everything to be properly initialized before that point in time.
199 *
200 * Return:
201 * * NULL if an error happened with creating the device
202 * * pointer to a valid struct faux_device that is registered with sysfs
203 */
204struct faux_device *faux_device_create(const char *name,
205 struct device *parent,
206 const struct faux_device_ops *faux_ops)
207{
208 return faux_device_create_with_groups(name, parent, faux_ops, NULL);
209}
210EXPORT_SYMBOL_GPL(faux_device_create);
211
212/**
213 * faux_device_destroy - destroy a faux device
214 * @faux_dev: faux device to destroy
215 *
216 * Unregisters and cleans up a device that was created with a call to
217 * faux_device_create()
218 */
219void faux_device_destroy(struct faux_device *faux_dev)
220{
221 struct device *dev = &faux_dev->dev;
222
223 if (!faux_dev)
224 return;
225
226 device_del(dev);
227
228 /* The final put_device() will clean up the memory we allocated for this device. */
229 put_device(dev);
230}
231EXPORT_SYMBOL_GPL(faux_device_destroy);
232
233int __init faux_bus_init(void)
234{
235 int ret;
236
237 faux_bus_root = kzalloc_obj(*faux_bus_root);
238 if (!faux_bus_root)
239 return -ENOMEM;
240
241 dev_set_name(faux_bus_root, "faux");
242
243 ret = device_register(faux_bus_root);
244 if (ret) {
245 put_device(faux_bus_root);
246 return ret;
247 }
248
249 ret = bus_register(&faux_bus_type);
250 if (ret)
251 goto error_bus;
252
253 ret = driver_register(&faux_driver);
254 if (ret)
255 goto error_driver;
256
257 return ret;
258
259error_driver:
260 bus_unregister(&faux_bus_type);
261
262error_bus:
263 device_unregister(faux_bus_root);
264 return ret;
265}