1 // SPDX-License-Identifier: GPL-2.0 2 /* 3 * Sample kset and ktype implementation 4 * 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/slab.h> 12 #include <linux/module.h> 13 #include <linux/init.h> 14 15 /* 16 * This module shows how to create a kset in sysfs called 17 * /sys/kernel/kset_example 18 * Then three kobjects are created and assigned to this kset, "foo", "baz", 19 * and "bar". In those kobjects, attributes of the same name are also 20 * created and if an integer is written to these files, it can be later 21 * read out of it. 22 */ 23 24 25 /* 26 * This is our "object" that we will create a few of and register them with 27 * sysfs. 28 */ 29 struct foo_obj { 30 struct kobject kobj; 31 int foo; 32 int baz; 33 int bar; 34 }; 35 #define to_foo_obj(x) container_of(x, struct foo_obj, kobj) 36 37 /* a custom attribute that works just for a struct foo_obj. */ 38 struct foo_attribute { 39 struct attribute attr; 40 ssize_t (*show)(struct foo_obj *foo, struct foo_attribute *attr, char *buf); 41 ssize_t (*store)(struct foo_obj *foo, struct foo_attribute *attr, const char *buf, size_t count); 42 }; 43 #define to_foo_attr(x) container_of(x, struct foo_attribute, attr) 44 45 /* 46 * The default show function that must be passed to sysfs. This will be 47 * called by sysfs for whenever a show function is called by the user on a 48 * sysfs file associated with the kobjects we have registered. We need to 49 * transpose back from a "default" kobject to our custom struct foo_obj and 50 * then call the show function for that specific object. 51 */ 52 static ssize_t foo_attr_show(struct kobject *kobj, 53 struct attribute *attr, 54 char *buf) 55 { 56 struct foo_attribute *attribute; 57 struct foo_obj *foo; 58 59 attribute = to_foo_attr(attr); 60 foo = to_foo_obj(kobj); 61 62 if (!attribute->show) 63 return -EIO; 64 65 return attribute->show(foo, attribute, buf); 66 } 67 68 /* 69 * Just like the default show function above, but this one is for when the 70 * sysfs "store" is requested (when a value is written to a file.) 71 */ 72 static ssize_t foo_attr_store(struct kobject *kobj, 73 struct attribute *attr, 74 const char *buf, size_t len) 75 { 76 struct foo_attribute *attribute; 77 struct foo_obj *foo; 78 79 attribute = to_foo_attr(attr); 80 foo = to_foo_obj(kobj); 81 82 if (!attribute->store) 83 return -EIO; 84 85 return attribute->store(foo, attribute, buf, len); 86 } 87 88 /* Our custom sysfs_ops that we will associate with our ktype later on */ 89 static const struct sysfs_ops foo_sysfs_ops = { 90 .show = foo_attr_show, 91 .store = foo_attr_store, 92 }; 93 94 /* 95 * The release function for our object. This is REQUIRED by the kernel to 96 * have. We free the memory held in our object here. 97 * 98 * NEVER try to get away with just a "blank" release function to try to be 99 * smarter than the kernel. Turns out, no one ever is... 100 */ 101 static void foo_release(struct kobject *kobj) 102 { 103 struct foo_obj *foo; 104 105 foo = to_foo_obj(kobj); 106 kfree(foo); 107 } 108 109 /* 110 * The "foo" file where the .foo variable is read from and written to. 111 */ 112 static ssize_t foo_show(struct foo_obj *foo_obj, struct foo_attribute *attr, 113 char *buf) 114 { 115 return sysfs_emit(buf, "%d\n", foo_obj->foo); 116 } 117 118 static ssize_t foo_store(struct foo_obj *foo_obj, struct foo_attribute *attr, 119 const char *buf, size_t count) 120 { 121 int ret; 122 123 ret = kstrtoint(buf, 10, &foo_obj->foo); 124 if (ret < 0) 125 return ret; 126 127 return count; 128 } 129 130 /* Sysfs attributes cannot be world-writable. */ 131 static struct foo_attribute foo_attribute = 132 __ATTR(foo, 0664, foo_show, foo_store); 133 134 /* 135 * More complex function where we determine which variable is being accessed by 136 * looking at the attribute for the "baz" and "bar" files. 137 */ 138 static ssize_t b_show(struct foo_obj *foo_obj, struct foo_attribute *attr, 139 char *buf) 140 { 141 int var; 142 143 if (strcmp(attr->attr.name, "baz") == 0) 144 var = foo_obj->baz; 145 else 146 var = foo_obj->bar; 147 return sysfs_emit(buf, "%d\n", var); 148 } 149 150 static ssize_t b_store(struct foo_obj *foo_obj, struct foo_attribute *attr, 151 const char *buf, size_t count) 152 { 153 int var, ret; 154 155 ret = kstrtoint(buf, 10, &var); 156 if (ret < 0) 157 return ret; 158 159 if (strcmp(attr->attr.name, "baz") == 0) 160 foo_obj->baz = var; 161 else 162 foo_obj->bar = var; 163 return count; 164 } 165 166 static struct foo_attribute baz_attribute = 167 __ATTR(baz, 0664, b_show, b_store); 168 static struct foo_attribute bar_attribute = 169 __ATTR(bar, 0664, b_show, b_store); 170 171 /* 172 * Create a group of attributes so that we can create and destroy them all 173 * at once. 174 */ 175 static struct attribute *foo_default_attrs[] = { 176 &foo_attribute.attr, 177 &baz_attribute.attr, 178 &bar_attribute.attr, 179 NULL, /* need to NULL terminate the list of attributes */ 180 }; 181 182 static umode_t foo_default_attrs_is_visible(struct kobject *kobj, 183 struct attribute *attr, 184 int n) 185 { 186 /* Hide attributes with the same name as the kobject. */ 187 if (strcmp(kobject_name(kobj), attr->name) == 0) 188 return 0; 189 return attr->mode; 190 } 191 192 static const struct attribute_group foo_default_group = { 193 .attrs = foo_default_attrs, 194 .is_visible = foo_default_attrs_is_visible, 195 }; 196 __ATTRIBUTE_GROUPS(foo_default); 197 198 /* 199 * Our own ktype for our kobjects. Here we specify our sysfs ops, the 200 * release function, and the set of default attributes we want created 201 * whenever a kobject of this type is registered with the kernel. 202 */ 203 static const struct kobj_type foo_ktype = { 204 .sysfs_ops = &foo_sysfs_ops, 205 .release = foo_release, 206 .default_groups = foo_default_groups, 207 }; 208 209 static struct kset *example_kset; 210 static struct foo_obj *foo_obj; 211 static struct foo_obj *bar_obj; 212 static struct foo_obj *baz_obj; 213 214 static struct foo_obj *create_foo_obj(const char *name) 215 { 216 struct foo_obj *foo; 217 int retval; 218 219 /* allocate the memory for the whole object */ 220 foo = kzalloc(sizeof(*foo), GFP_KERNEL); 221 if (!foo) 222 return NULL; 223 224 /* 225 * As we have a kset for this kobject, we need to set it before calling 226 * the kobject core. 227 */ 228 foo->kobj.kset = example_kset; 229 230 /* 231 * Initialize and add the kobject to the kernel. All the default files 232 * will be created here. As we have already specified a kset for this 233 * kobject, we don't have to set a parent for the kobject, the kobject 234 * will be placed beneath that kset automatically. 235 */ 236 retval = kobject_init_and_add(&foo->kobj, &foo_ktype, NULL, "%s", name); 237 if (retval) { 238 kobject_put(&foo->kobj); 239 return NULL; 240 } 241 242 /* 243 * We are always responsible for sending the uevent that the kobject 244 * was added to the system. 245 */ 246 kobject_uevent(&foo->kobj, KOBJ_ADD); 247 248 return foo; 249 } 250 251 static void destroy_foo_obj(struct foo_obj *foo) 252 { 253 kobject_put(&foo->kobj); 254 } 255 256 static int __init example_init(void) 257 { 258 /* 259 * Create a kset with the name of "kset_example", 260 * located under /sys/kernel/ 261 */ 262 example_kset = kset_create_and_add("kset_example", NULL, kernel_kobj); 263 if (!example_kset) 264 return -ENOMEM; 265 266 /* 267 * Create three objects and register them with our kset 268 */ 269 foo_obj = create_foo_obj("foo"); 270 if (!foo_obj) 271 goto foo_error; 272 273 bar_obj = create_foo_obj("bar"); 274 if (!bar_obj) 275 goto bar_error; 276 277 baz_obj = create_foo_obj("baz"); 278 if (!baz_obj) 279 goto baz_error; 280 281 return 0; 282 283 baz_error: 284 destroy_foo_obj(bar_obj); 285 bar_error: 286 destroy_foo_obj(foo_obj); 287 foo_error: 288 kset_unregister(example_kset); 289 return -EINVAL; 290 } 291 292 static void __exit example_exit(void) 293 { 294 destroy_foo_obj(baz_obj); 295 destroy_foo_obj(bar_obj); 296 destroy_foo_obj(foo_obj); 297 kset_unregister(example_kset); 298 } 299 300 module_init(example_init); 301 module_exit(example_exit); 302 MODULE_DESCRIPTION("Sample kset and ktype implementation"); 303 MODULE_LICENSE("GPL v2"); 304 MODULE_AUTHOR("Greg Kroah-Hartman <greg@kroah.com>"); 305