1 | // SPDX-License-Identifier: GPL-2.0 |
2 | /* |
3 | * Sample kset and ktype implementation |
4 | * |
5 | * Copyright (C) 2004-2007 Greg Kroah-Hartman <greg@kroah.com> |
6 | * Copyright (C) 2007 Novell Inc. |
7 | */ |
8 | #include <linux/kobject.h> |
9 | #include <linux/string.h> |
10 | #include <linux/sysfs.h> |
11 | #include <linux/slab.h> |
12 | #include <linux/module.h> |
13 | #include <linux/init.h> |
14 | |
15 | /* |
16 | * This module shows how to create a kset in sysfs called |
17 | * /sys/kernel/kset-example |
18 | * Then tree kobjects are created and assigned to this kset, "foo", "baz", |
19 | * and "bar". In those kobjects, attributes of the same name are also |
20 | * created and if an integer is written to these files, it can be later |
21 | * read out of it. |
22 | */ |
23 | |
24 | |
25 | /* |
26 | * This is our "object" that we will create a few of and register them with |
27 | * sysfs. |
28 | */ |
29 | struct foo_obj { |
30 | struct kobject kobj; |
31 | int foo; |
32 | int baz; |
33 | int bar; |
34 | }; |
35 | #define to_foo_obj(x) container_of(x, struct foo_obj, kobj) |
36 | |
37 | /* a custom attribute that works just for a struct foo_obj. */ |
38 | struct foo_attribute { |
39 | struct attribute attr; |
40 | ssize_t (*show)(struct foo_obj *foo, struct foo_attribute *attr, char *buf); |
41 | ssize_t (*store)(struct foo_obj *foo, struct foo_attribute *attr, const char *buf, size_t count); |
42 | }; |
43 | #define to_foo_attr(x) container_of(x, struct foo_attribute, attr) |
44 | |
45 | /* |
46 | * The default show function that must be passed to sysfs. This will be |
47 | * called by sysfs for whenever a show function is called by the user on a |
48 | * sysfs file associated with the kobjects we have registered. We need to |
49 | * transpose back from a "default" kobject to our custom struct foo_obj and |
50 | * then call the show function for that specific object. |
51 | */ |
52 | static ssize_t foo_attr_show(struct kobject *kobj, |
53 | struct attribute *attr, |
54 | char *buf) |
55 | { |
56 | struct foo_attribute *attribute; |
57 | struct foo_obj *foo; |
58 | |
59 | attribute = to_foo_attr(attr); |
60 | foo = to_foo_obj(kobj); |
61 | |
62 | if (!attribute->show) |
63 | return -EIO; |
64 | |
65 | return attribute->show(foo, attribute, buf); |
66 | } |
67 | |
68 | /* |
69 | * Just like the default show function above, but this one is for when the |
70 | * sysfs "store" is requested (when a value is written to a file.) |
71 | */ |
72 | static ssize_t foo_attr_store(struct kobject *kobj, |
73 | struct attribute *attr, |
74 | const char *buf, size_t len) |
75 | { |
76 | struct foo_attribute *attribute; |
77 | struct foo_obj *foo; |
78 | |
79 | attribute = to_foo_attr(attr); |
80 | foo = to_foo_obj(kobj); |
81 | |
82 | if (!attribute->store) |
83 | return -EIO; |
84 | |
85 | return attribute->store(foo, attribute, buf, len); |
86 | } |
87 | |
88 | /* Our custom sysfs_ops that we will associate with our ktype later on */ |
89 | static const struct sysfs_ops foo_sysfs_ops = { |
90 | .show = foo_attr_show, |
91 | .store = foo_attr_store, |
92 | }; |
93 | |
94 | /* |
95 | * The release function for our object. This is REQUIRED by the kernel to |
96 | * have. We free the memory held in our object here. |
97 | * |
98 | * NEVER try to get away with just a "blank" release function to try to be |
99 | * smarter than the kernel. Turns out, no one ever is... |
100 | */ |
101 | static void foo_release(struct kobject *kobj) |
102 | { |
103 | struct foo_obj *foo; |
104 | |
105 | foo = to_foo_obj(kobj); |
106 | kfree(objp: foo); |
107 | } |
108 | |
109 | /* |
110 | * The "foo" file where the .foo variable is read from and written to. |
111 | */ |
112 | static ssize_t foo_show(struct foo_obj *foo_obj, struct foo_attribute *attr, |
113 | char *buf) |
114 | { |
115 | return sysfs_emit(buf, fmt: "%d\n" , foo_obj->foo); |
116 | } |
117 | |
118 | static ssize_t foo_store(struct foo_obj *foo_obj, struct foo_attribute *attr, |
119 | const char *buf, size_t count) |
120 | { |
121 | int ret; |
122 | |
123 | ret = kstrtoint(s: buf, base: 10, res: &foo_obj->foo); |
124 | if (ret < 0) |
125 | return ret; |
126 | |
127 | return count; |
128 | } |
129 | |
130 | /* Sysfs attributes cannot be world-writable. */ |
131 | static struct foo_attribute foo_attribute = |
132 | __ATTR(foo, 0664, foo_show, foo_store); |
133 | |
134 | /* |
135 | * More complex function where we determine which variable is being accessed by |
136 | * looking at the attribute for the "baz" and "bar" files. |
137 | */ |
138 | static ssize_t b_show(struct foo_obj *foo_obj, struct foo_attribute *attr, |
139 | char *buf) |
140 | { |
141 | int var; |
142 | |
143 | if (strcmp(attr->attr.name, "baz" ) == 0) |
144 | var = foo_obj->baz; |
145 | else |
146 | var = foo_obj->bar; |
147 | return sysfs_emit(buf, fmt: "%d\n" , var); |
148 | } |
149 | |
150 | static ssize_t b_store(struct foo_obj *foo_obj, struct foo_attribute *attr, |
151 | const char *buf, size_t count) |
152 | { |
153 | int var, ret; |
154 | |
155 | ret = kstrtoint(s: buf, base: 10, res: &var); |
156 | if (ret < 0) |
157 | return ret; |
158 | |
159 | if (strcmp(attr->attr.name, "baz" ) == 0) |
160 | foo_obj->baz = var; |
161 | else |
162 | foo_obj->bar = var; |
163 | return count; |
164 | } |
165 | |
166 | static struct foo_attribute baz_attribute = |
167 | __ATTR(baz, 0664, b_show, b_store); |
168 | static struct foo_attribute bar_attribute = |
169 | __ATTR(bar, 0664, b_show, b_store); |
170 | |
171 | /* |
172 | * Create a group of attributes so that we can create and destroy them all |
173 | * at once. |
174 | */ |
175 | static struct attribute *foo_default_attrs[] = { |
176 | &foo_attribute.attr, |
177 | &baz_attribute.attr, |
178 | &bar_attribute.attr, |
179 | NULL, /* need to NULL terminate the list of attributes */ |
180 | }; |
181 | ATTRIBUTE_GROUPS(foo_default); |
182 | |
183 | /* |
184 | * Our own ktype for our kobjects. Here we specify our sysfs ops, the |
185 | * release function, and the set of default attributes we want created |
186 | * whenever a kobject of this type is registered with the kernel. |
187 | */ |
188 | static const struct kobj_type foo_ktype = { |
189 | .sysfs_ops = &foo_sysfs_ops, |
190 | .release = foo_release, |
191 | .default_groups = foo_default_groups, |
192 | }; |
193 | |
194 | static struct kset *example_kset; |
195 | static struct foo_obj *foo_obj; |
196 | static struct foo_obj *bar_obj; |
197 | static struct foo_obj *baz_obj; |
198 | |
199 | static struct foo_obj *create_foo_obj(const char *name) |
200 | { |
201 | struct foo_obj *foo; |
202 | int retval; |
203 | |
204 | /* allocate the memory for the whole object */ |
205 | foo = kzalloc(size: sizeof(*foo), GFP_KERNEL); |
206 | if (!foo) |
207 | return NULL; |
208 | |
209 | /* |
210 | * As we have a kset for this kobject, we need to set it before calling |
211 | * the kobject core. |
212 | */ |
213 | foo->kobj.kset = example_kset; |
214 | |
215 | /* |
216 | * Initialize and add the kobject to the kernel. All the default files |
217 | * will be created here. As we have already specified a kset for this |
218 | * kobject, we don't have to set a parent for the kobject, the kobject |
219 | * will be placed beneath that kset automatically. |
220 | */ |
221 | retval = kobject_init_and_add(kobj: &foo->kobj, ktype: &foo_ktype, NULL, fmt: "%s" , name); |
222 | if (retval) { |
223 | kobject_put(kobj: &foo->kobj); |
224 | return NULL; |
225 | } |
226 | |
227 | /* |
228 | * We are always responsible for sending the uevent that the kobject |
229 | * was added to the system. |
230 | */ |
231 | kobject_uevent(kobj: &foo->kobj, action: KOBJ_ADD); |
232 | |
233 | return foo; |
234 | } |
235 | |
236 | static void destroy_foo_obj(struct foo_obj *foo) |
237 | { |
238 | kobject_put(kobj: &foo->kobj); |
239 | } |
240 | |
241 | static int __init example_init(void) |
242 | { |
243 | /* |
244 | * Create a kset with the name of "kset_example", |
245 | * located under /sys/kernel/ |
246 | */ |
247 | example_kset = kset_create_and_add(name: "kset_example" , NULL, parent_kobj: kernel_kobj); |
248 | if (!example_kset) |
249 | return -ENOMEM; |
250 | |
251 | /* |
252 | * Create three objects and register them with our kset |
253 | */ |
254 | foo_obj = create_foo_obj(name: "foo" ); |
255 | if (!foo_obj) |
256 | goto foo_error; |
257 | |
258 | bar_obj = create_foo_obj(name: "bar" ); |
259 | if (!bar_obj) |
260 | goto bar_error; |
261 | |
262 | baz_obj = create_foo_obj(name: "baz" ); |
263 | if (!baz_obj) |
264 | goto baz_error; |
265 | |
266 | return 0; |
267 | |
268 | baz_error: |
269 | destroy_foo_obj(foo: bar_obj); |
270 | bar_error: |
271 | destroy_foo_obj(foo: foo_obj); |
272 | foo_error: |
273 | kset_unregister(kset: example_kset); |
274 | return -EINVAL; |
275 | } |
276 | |
277 | static void __exit example_exit(void) |
278 | { |
279 | destroy_foo_obj(foo: baz_obj); |
280 | destroy_foo_obj(foo: bar_obj); |
281 | destroy_foo_obj(foo: foo_obj); |
282 | kset_unregister(kset: example_kset); |
283 | } |
284 | |
285 | module_init(example_init); |
286 | module_exit(example_exit); |
287 | MODULE_LICENSE("GPL v2" ); |
288 | MODULE_AUTHOR("Greg Kroah-Hartman <greg@kroah.com>" ); |
289 | |