Linux Kernel  3.7.1
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kobject-example.c
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1 /*
2  * Sample kobject implementation
3  *
4  * Copyright (C) 2004-2007 Greg Kroah-Hartman <[email protected]>
5  * Copyright (C) 2007 Novell Inc.
6  *
7  * Released under the GPL version 2 only.
8  *
9  */
10 #include <linux/kobject.h>
11 #include <linux/string.h>
12 #include <linux/sysfs.h>
13 #include <linux/module.h>
14 #include <linux/init.h>
15 
16 /*
17  * This module shows how to create a simple subdirectory in sysfs called
18  * /sys/kernel/kobject-example In that directory, 3 files are created:
19  * "foo", "baz", and "bar". If an integer is written to these files, it can be
20  * later read out of it.
21  */
22 
23 static int foo;
24 static int baz;
25 static int bar;
26 
27 /*
28  * The "foo" file where a static variable is read from and written to.
29  */
30 static ssize_t foo_show(struct kobject *kobj, struct kobj_attribute *attr,
31  char *buf)
32 {
33  return sprintf(buf, "%d\n", foo);
34 }
35 
36 static ssize_t foo_store(struct kobject *kobj, struct kobj_attribute *attr,
37  const char *buf, size_t count)
38 {
39  sscanf(buf, "%du", &foo);
40  return count;
41 }
42 
43 static struct kobj_attribute foo_attribute =
44  __ATTR(foo, 0666, foo_show, foo_store);
45 
46 /*
47  * More complex function where we determine which variable is being accessed by
48  * looking at the attribute for the "baz" and "bar" files.
49  */
50 static ssize_t b_show(struct kobject *kobj, struct kobj_attribute *attr,
51  char *buf)
52 {
53  int var;
54 
55  if (strcmp(attr->attr.name, "baz") == 0)
56  var = baz;
57  else
58  var = bar;
59  return sprintf(buf, "%d\n", var);
60 }
61 
62 static ssize_t b_store(struct kobject *kobj, struct kobj_attribute *attr,
63  const char *buf, size_t count)
64 {
65  int var;
66 
67  sscanf(buf, "%du", &var);
68  if (strcmp(attr->attr.name, "baz") == 0)
69  baz = var;
70  else
71  bar = var;
72  return count;
73 }
74 
75 static struct kobj_attribute baz_attribute =
76  __ATTR(baz, 0666, b_show, b_store);
77 static struct kobj_attribute bar_attribute =
78  __ATTR(bar, 0666, b_show, b_store);
79 
80 
81 /*
82  * Create a group of attributes so that we can create and destroy them all
83  * at once.
84  */
85 static struct attribute *attrs[] = {
86  &foo_attribute.attr,
87  &baz_attribute.attr,
88  &bar_attribute.attr,
89  NULL, /* need to NULL terminate the list of attributes */
90 };
91 
92 /*
93  * An unnamed attribute group will put all of the attributes directly in
94  * the kobject directory. If we specify a name, a subdirectory will be
95  * created for the attributes with the directory being the name of the
96  * attribute group.
97  */
98 static struct attribute_group attr_group = {
99  .attrs = attrs,
100 };
101 
102 static struct kobject *example_kobj;
103 
104 static int __init example_init(void)
105 {
106  int retval;
107 
108  /*
109  * Create a simple kobject with the name of "kobject_example",
110  * located under /sys/kernel/
111  *
112  * As this is a simple directory, no uevent will be sent to
113  * userspace. That is why this function should not be used for
114  * any type of dynamic kobjects, where the name and number are
115  * not known ahead of time.
116  */
117  example_kobj = kobject_create_and_add("kobject_example", kernel_kobj);
118  if (!example_kobj)
119  return -ENOMEM;
120 
121  /* Create the files associated with this kobject */
122  retval = sysfs_create_group(example_kobj, &attr_group);
123  if (retval)
124  kobject_put(example_kobj);
125 
126  return retval;
127 }
128 
129 static void __exit example_exit(void)
130 {
131  kobject_put(example_kobj);
132 }
133 
134 module_init(example_init);
135 module_exit(example_exit);
136 MODULE_LICENSE("GPL");
137 MODULE_AUTHOR("Greg Kroah-Hartman <[email protected]>");