samples/kobject/kobject-example.c

   1 /*
   2  * Sample kobject implementation
   3  *
   4  * Copyright (C) 2004-2007 Greg Kroah-Hartman <greg@kroah.com>
   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 <greg@kroah.com>");