1 | // SPDX-License-Identifier: GPL-2.0 |
2 | /* |
3 | * Sample kobject 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/module.h> |
12 | #include <linux/init.h> |
13 | |
14 | /* |
15 | * This module shows how to create a simple subdirectory in sysfs called |
16 | * /sys/kernel/kobject-example In that directory, 3 files are created: |
17 | * "foo", "baz", and "bar". If an integer is written to these files, it can be |
18 | * later read out of it. |
19 | */ |
20 | |
21 | static int foo; |
22 | static int baz; |
23 | static int bar; |
24 | |
25 | /* |
26 | * The "foo" file where a static variable is read from and written to. |
27 | */ |
28 | static ssize_t foo_show(struct kobject *kobj, struct kobj_attribute *attr, |
29 | char *buf) |
30 | { |
31 | return sysfs_emit(buf, fmt: "%d\n" , foo); |
32 | } |
33 | |
34 | static ssize_t foo_store(struct kobject *kobj, struct kobj_attribute *attr, |
35 | const char *buf, size_t count) |
36 | { |
37 | int ret; |
38 | |
39 | ret = kstrtoint(s: buf, base: 10, res: &foo); |
40 | if (ret < 0) |
41 | return ret; |
42 | |
43 | return count; |
44 | } |
45 | |
46 | /* Sysfs attributes cannot be world-writable. */ |
47 | static struct kobj_attribute foo_attribute = |
48 | __ATTR(foo, 0664, foo_show, foo_store); |
49 | |
50 | /* |
51 | * More complex function where we determine which variable is being accessed by |
52 | * looking at the attribute for the "baz" and "bar" files. |
53 | */ |
54 | static ssize_t b_show(struct kobject *kobj, struct kobj_attribute *attr, |
55 | char *buf) |
56 | { |
57 | int var; |
58 | |
59 | if (strcmp(attr->attr.name, "baz" ) == 0) |
60 | var = baz; |
61 | else |
62 | var = bar; |
63 | return sysfs_emit(buf, fmt: "%d\n" , var); |
64 | } |
65 | |
66 | static ssize_t b_store(struct kobject *kobj, struct kobj_attribute *attr, |
67 | const char *buf, size_t count) |
68 | { |
69 | int var, ret; |
70 | |
71 | ret = kstrtoint(s: buf, base: 10, res: &var); |
72 | if (ret < 0) |
73 | return ret; |
74 | |
75 | if (strcmp(attr->attr.name, "baz" ) == 0) |
76 | baz = var; |
77 | else |
78 | bar = var; |
79 | return count; |
80 | } |
81 | |
82 | static struct kobj_attribute baz_attribute = |
83 | __ATTR(baz, 0664, b_show, b_store); |
84 | static struct kobj_attribute bar_attribute = |
85 | __ATTR(bar, 0664, b_show, b_store); |
86 | |
87 | |
88 | /* |
89 | * Create a group of attributes so that we can create and destroy them all |
90 | * at once. |
91 | */ |
92 | static struct attribute *attrs[] = { |
93 | &foo_attribute.attr, |
94 | &baz_attribute.attr, |
95 | &bar_attribute.attr, |
96 | NULL, /* need to NULL terminate the list of attributes */ |
97 | }; |
98 | |
99 | /* |
100 | * An unnamed attribute group will put all of the attributes directly in |
101 | * the kobject directory. If we specify a name, a subdirectory will be |
102 | * created for the attributes with the directory being the name of the |
103 | * attribute group. |
104 | */ |
105 | static struct attribute_group attr_group = { |
106 | .attrs = attrs, |
107 | }; |
108 | |
109 | static struct kobject *example_kobj; |
110 | |
111 | static int __init example_init(void) |
112 | { |
113 | int retval; |
114 | |
115 | /* |
116 | * Create a simple kobject with the name of "kobject_example", |
117 | * located under /sys/kernel/ |
118 | * |
119 | * As this is a simple directory, no uevent will be sent to |
120 | * userspace. That is why this function should not be used for |
121 | * any type of dynamic kobjects, where the name and number are |
122 | * not known ahead of time. |
123 | */ |
124 | example_kobj = kobject_create_and_add(name: "kobject_example" , parent: kernel_kobj); |
125 | if (!example_kobj) |
126 | return -ENOMEM; |
127 | |
128 | /* Create the files associated with this kobject */ |
129 | retval = sysfs_create_group(kobj: example_kobj, grp: &attr_group); |
130 | if (retval) |
131 | kobject_put(kobj: example_kobj); |
132 | |
133 | return retval; |
134 | } |
135 | |
136 | static void __exit example_exit(void) |
137 | { |
138 | kobject_put(kobj: example_kobj); |
139 | } |
140 | |
141 | module_init(example_init); |
142 | module_exit(example_exit); |
143 | MODULE_LICENSE("GPL v2" ); |
144 | MODULE_AUTHOR("Greg Kroah-Hartman <greg@kroah.com>" ); |
145 | |