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 /* Sysfs attributes cannot be world-writable. */
  44 static struct kobj_attribute foo_attribute =
  45         __ATTR(foo, 0664, foo_show, foo_store);
  46
  47 /*
  48  * More complex function where we determine which variable is being accessed by
  49  * looking at the attribute for the "baz" and "bar" files.
  50  */
  51 static ssize_t b_show(struct kobject *kobj, struct kobj_attribute *attr,
  52                       char *buf)
  53 {
  54         int var;
  55
  56         if (strcmp(attr->attr.name, "baz") == 0)
  57                 var = baz;
  58         else
  59                 var = bar;
  60         return sprintf(buf, "%d\n", var);
  61 }
  62
  63 static ssize_t b_store(struct kobject *kobj, struct kobj_attribute *attr,
  64                        const char *buf, size_t count)
  65 {
  66         int var;
  67
  68         sscanf(buf, "%du", &var);
  69         if (strcmp(attr->attr.name, "baz") == 0)
  70                 baz = var;
  71         else
  72                 bar = var;
  73         return count;
  74 }
  75
  76 static struct kobj_attribute baz_attribute =
  77         __ATTR(baz, 0664, b_show, b_store);
  78 static struct kobj_attribute bar_attribute =
  79         __ATTR(bar, 0664, b_show, b_store);
  80
  81
  82 /*
  83  * Create a group of attributes so that we can create and destroy them all
  84  * at once.
  85  */
  86 static struct attribute *attrs[] = {
  87         &foo_attribute.attr,
  88         &baz_attribute.attr,
  89         &bar_attribute.attr,
  90         NULL,   /* need to NULL terminate the list of attributes */
  91 };
  92
  93 /*
  94  * An unnamed attribute group will put all of the attributes directly in
  95  * the kobject directory.  If we specify a name, a subdirectory will be
  96  * created for the attributes with the directory being the name of the
  97  * attribute group.
  98  */
  99 static struct attribute_group attr_group = {
 100         .attrs = attrs,
 101 };
 102
 103 static struct kobject *example_kobj;
 104
 105 static int __init example_init(void)
 106 {
 107         int retval;
 108
 109         /*
 110          * Create a simple kobject with the name of "kobject_example",
 111          * located under /sys/kernel/
 112          *
 113          * As this is a simple directory, no uevent will be sent to
 114          * userspace.  That is why this function should not be used for
 115          * any type of dynamic kobjects, where the name and number are
 116          * not known ahead of time.
 117          */
 118         example_kobj = kobject_create_and_add("kobject_example", kernel_kobj);
 119         if (!example_kobj)
 120                 return -ENOMEM;
 121
 122         /* Create the files associated with this kobject */
 123         retval = sysfs_create_group(example_kobj, &attr_group);
 124         if (retval)
 125                 kobject_put(example_kobj);
 126
 127         return retval;
 128 }
 129
 130 static void __exit example_exit(void)
 131 {
 132         kobject_put(example_kobj);
 133 }
 134
 135 module_init(example_init);
 136 module_exit(example_exit);
 137 MODULE_LICENSE("GPL");
 138 MODULE_AUTHOR("Greg Kroah-Hartman <greg@kroah.com>");