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         int ret;
  40
  41         ret = kstrtoint(buf, 10, &foo);
  42         if (ret < 0)
  43                 return ret;
  44
  45         return count;
  46 }
  47
  48 /* Sysfs attributes cannot be world-writable. */
  49 static struct kobj_attribute foo_attribute =
  50         __ATTR(foo, 0664, foo_show, foo_store);
  51
  52 /*
  53  * More complex function where we determine which variable is being accessed by
  54  * looking at the attribute for the "baz" and "bar" files.
  55  */
  56 static ssize_t b_show(struct kobject *kobj, struct kobj_attribute *attr,
  57                       char *buf)
  58 {
  59         int var;
  60
  61         if (strcmp(attr->attr.name, "baz") == 0)
  62                 var = baz;
  63         else
  64                 var = bar;
  65         return sprintf(buf, "%d\n", var);
  66 }
  67
  68 static ssize_t b_store(struct kobject *kobj, struct kobj_attribute *attr,
  69                        const char *buf, size_t count)
  70 {
  71         int var, ret;
  72
  73         ret = kstrtoint(buf, 10, &var);
  74         if (ret < 0)
  75                 return ret;
  76
  77         if (strcmp(attr->attr.name, "baz") == 0)
  78                 baz = var;
  79         else
  80                 bar = var;
  81         return count;
  82 }
  83
  84 static struct kobj_attribute baz_attribute =
  85         __ATTR(baz, 0664, b_show, b_store);
  86 static struct kobj_attribute bar_attribute =
  87         __ATTR(bar, 0664, b_show, b_store);
  88
  89
  90 /*
  91  * Create a group of attributes so that we can create and destroy them all
  92  * at once.
  93  */
  94 static struct attribute *attrs[] = {
  95         &foo_attribute.attr,
  96         &baz_attribute.attr,
  97         &bar_attribute.attr,
  98         NULL,   /* need to NULL terminate the list of attributes */
  99 };
 100
 101 /*
 102  * An unnamed attribute group will put all of the attributes directly in
 103  * the kobject directory.  If we specify a name, a subdirectory will be
 104  * created for the attributes with the directory being the name of the
 105  * attribute group.
 106  */
 107 static struct attribute_group attr_group = {
 108         .attrs = attrs,
 109 };
 110
 111 static struct kobject *example_kobj;
 112
 113 static int __init example_init(void)
 114 {
 115         int retval;
 116
 117         /*
 118          * Create a simple kobject with the name of "kobject_example",
 119          * located under /sys/kernel/
 120          *
 121          * As this is a simple directory, no uevent will be sent to
 122          * userspace.  That is why this function should not be used for
 123          * any type of dynamic kobjects, where the name and number are
 124          * not known ahead of time.
 125          */
 126         example_kobj = kobject_create_and_add("kobject_example", kernel_kobj);
 127         if (!example_kobj)
 128                 return -ENOMEM;
 129
 130         /* Create the files associated with this kobject */
 131         retval = sysfs_create_group(example_kobj, &attr_group);
 132         if (retval)
 133                 kobject_put(example_kobj);
 134
 135         return retval;
 136 }
 137
 138 static void __exit example_exit(void)
 139 {
 140         kobject_put(example_kobj);
 141 }
 142
 143 module_init(example_init);
 144 module_exit(example_exit);
 145 MODULE_LICENSE("GPL v2");
 146 MODULE_AUTHOR("Greg Kroah-Hartman <greg@kroah.com>");