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d9d16e16 | 1 | // SPDX-License-Identifier: GPL-2.0 |
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2 | /* |
3 | * Sample kobject implementation | |
4 | * | |
5 | * Copyright (C) 2004-2007 Greg Kroah-Hartman <greg@kroah.com> | |
6 | * Copyright (C) 2007 Novell Inc. | |
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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 sprintf(buf, "%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 | { | |
5fd637e7 RB |
37 | int ret; |
38 | ||
39 | ret = kstrtoint(buf, 10, &foo); | |
40 | if (ret < 0) | |
41 | return ret; | |
42 | ||
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43 | return count; |
44 | } | |
45 | ||
de510989 | 46 | /* Sysfs attributes cannot be world-writable. */ |
40efcb05 | 47 | static struct kobj_attribute foo_attribute = |
de510989 | 48 | __ATTR(foo, 0664, foo_show, foo_store); |
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49 | |
50 | /* | |
a115bc07 | 51 | * More complex function where we determine which variable is being accessed by |
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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 sprintf(buf, "%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 | { | |
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69 | int var, ret; |
70 | ||
71 | ret = kstrtoint(buf, 10, &var); | |
72 | if (ret < 0) | |
73 | return ret; | |
40efcb05 | 74 | |
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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 = | |
de510989 | 83 | __ATTR(baz, 0664, b_show, b_store); |
40efcb05 | 84 | static struct kobj_attribute bar_attribute = |
de510989 | 85 | __ATTR(bar, 0664, b_show, b_store); |
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86 | |
87 | ||
88 | /* | |
a115bc07 | 89 | * Create a group of attributes so that we can create and destroy them all |
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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 | ||
7ec7fb39 | 111 | static int __init example_init(void) |
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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("kobject_example", kernel_kobj); | |
125 | if (!example_kobj) | |
126 | return -ENOMEM; | |
127 | ||
128 | /* Create the files associated with this kobject */ | |
129 | retval = sysfs_create_group(example_kobj, &attr_group); | |
130 | if (retval) | |
131 | kobject_put(example_kobj); | |
132 | ||
133 | return retval; | |
134 | } | |
135 | ||
7ec7fb39 | 136 | static void __exit example_exit(void) |
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137 | { |
138 | kobject_put(example_kobj); | |
139 | } | |
140 | ||
141 | module_init(example_init); | |
142 | module_exit(example_exit); | |
07afb6ac | 143 | MODULE_LICENSE("GPL v2"); |
40efcb05 | 144 | MODULE_AUTHOR("Greg Kroah-Hartman <greg@kroah.com>"); |