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 23static int foo; 24static int baz; 25static int bar; 26 27/* 28 * The "foo" file where a static variable is read from and written to. 29 */ 30static ssize_t foo_show(struct kobject *kobj, struct kobj_attribute *attr, 31 char *buf) 32{ 33 return sprintf(buf, "%d\n", foo); 34} 35 36static 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 43static 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 */ 50static 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 62static 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 75static struct kobj_attribute baz_attribute = 76 __ATTR(baz, 0666, b_show, b_store); 77static 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 */ 85static 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 */ 98static struct attribute_group attr_group = { 99 .attrs = attrs, 100}; 101 102static struct kobject *example_kobj; 103 104static 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 129static void __exit example_exit(void) 130{ 131 kobject_put(example_kobj); 132} 133 134module_init(example_init); 135module_exit(example_exit); 136MODULE_LICENSE("GPL"); 137MODULE_AUTHOR("Greg Kroah-Hartman <greg@kroah.com>"); 138