146 lines · c
1// SPDX-License-Identifier: GPL-2.02/*3 * Sample kobject implementation4 *5 * Copyright (C) 2004-2007 Greg Kroah-Hartman <greg@kroah.com>6 * Copyright (C) 2007 Novell Inc.7 */8#include <linux/kobject.h>9#include <linux/string.h>10#include <linux/sysfs.h>11#include <linux/module.h>12#include <linux/init.h>13 14/*15 * This module shows how to create a simple subdirectory in sysfs called16 * /sys/kernel/kobject-example In that directory, 3 files are created:17 * "foo", "baz", and "bar". If an integer is written to these files, it can be18 * later read out of it.19 */20 21static int foo;22static int baz;23static int bar;24 25/*26 * The "foo" file where a static variable is read from and written to.27 */28static ssize_t foo_show(struct kobject *kobj, struct kobj_attribute *attr,29 char *buf)30{31 return sysfs_emit(buf, "%d\n", foo);32}33 34static ssize_t foo_store(struct kobject *kobj, struct kobj_attribute *attr,35 const char *buf, size_t count)36{37 int ret;38 39 ret = kstrtoint(buf, 10, &foo);40 if (ret < 0)41 return ret;42 43 return count;44}45 46/* Sysfs attributes cannot be world-writable. */47static struct kobj_attribute foo_attribute =48 __ATTR(foo, 0664, foo_show, foo_store);49 50/*51 * More complex function where we determine which variable is being accessed by52 * looking at the attribute for the "baz" and "bar" files.53 */54static ssize_t b_show(struct kobject *kobj, struct kobj_attribute *attr,55 char *buf)56{57 int var;58 59 if (strcmp(attr->attr.name, "baz") == 0)60 var = baz;61 else62 var = bar;63 return sysfs_emit(buf, "%d\n", var);64}65 66static ssize_t b_store(struct kobject *kobj, struct kobj_attribute *attr,67 const char *buf, size_t count)68{69 int var, ret;70 71 ret = kstrtoint(buf, 10, &var);72 if (ret < 0)73 return ret;74 75 if (strcmp(attr->attr.name, "baz") == 0)76 baz = var;77 else78 bar = var;79 return count;80}81 82static struct kobj_attribute baz_attribute =83 __ATTR(baz, 0664, b_show, b_store);84static struct kobj_attribute bar_attribute =85 __ATTR(bar, 0664, b_show, b_store);86 87 88/*89 * Create a group of attributes so that we can create and destroy them all90 * at once.91 */92static struct attribute *attrs[] = {93 &foo_attribute.attr,94 &baz_attribute.attr,95 &bar_attribute.attr,96 NULL, /* need to NULL terminate the list of attributes */97};98 99/*100 * An unnamed attribute group will put all of the attributes directly in101 * the kobject directory. If we specify a name, a subdirectory will be102 * created for the attributes with the directory being the name of the103 * attribute group.104 */105static struct attribute_group attr_group = {106 .attrs = attrs,107};108 109static struct kobject *example_kobj;110 111static int __init example_init(void)112{113 int retval;114 115 /*116 * Create a simple kobject with the name of "kobject_example",117 * located under /sys/kernel/118 *119 * As this is a simple directory, no uevent will be sent to120 * userspace. That is why this function should not be used for121 * any type of dynamic kobjects, where the name and number are122 * not known ahead of time.123 */124 example_kobj = kobject_create_and_add("kobject_example", kernel_kobj);125 if (!example_kobj)126 return -ENOMEM;127 128 /* Create the files associated with this kobject */129 retval = sysfs_create_group(example_kobj, &attr_group);130 if (retval)131 kobject_put(example_kobj);132 133 return retval;134}135 136static void __exit example_exit(void)137{138 kobject_put(example_kobj);139}140 141module_init(example_init);142module_exit(example_exit);143MODULE_DESCRIPTION("Sample kobject implementation");144MODULE_LICENSE("GPL v2");145MODULE_AUTHOR("Greg Kroah-Hartman <greg@kroah.com>");146