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 tree 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 ATTRIBUTE_GROUPS(foo_default); 182 183 /* 184 * Our own ktype for our kobjects. Here we specify our sysfs ops, the 185 * release function, and the set of default attributes we want created 186 * whenever a kobject of this type is registered with the kernel. 187 */ 188 static const struct kobj_type foo_ktype = { 189 .sysfs_ops = &foo_sysfs_ops, 190 .release = foo_release, 191 .default_groups = foo_default_groups, 192 }; 193 194 static struct kset *example_kset; 195 static struct foo_obj *foo_obj; 196 static struct foo_obj *bar_obj; 197 static struct foo_obj *baz_obj; 198 199 static struct foo_obj *create_foo_obj(const char *name) 200 { 201 struct foo_obj *foo; 202 int retval; 203 204 /* allocate the memory for the whole object */ 205 foo = kzalloc(sizeof(*foo), GFP_KERNEL); 206 if (!foo) 207 return NULL; 208 209 /* 210 * As we have a kset for this kobject, we need to set it before calling 211 * the kobject core. 212 */ 213 foo->kobj.kset = example_kset; 214 215 /* 216 * Initialize and add the kobject to the kernel. All the default files 217 * will be created here. As we have already specified a kset for this 218 * kobject, we don't have to set a parent for the kobject, the kobject 219 * will be placed beneath that kset automatically. 220 */ 221 retval = kobject_init_and_add(&foo->kobj, &foo_ktype, NULL, "%s", name); 222 if (retval) { 223 kobject_put(&foo->kobj); 224 return NULL; 225 } 226 227 /* 228 * We are always responsible for sending the uevent that the kobject 229 * was added to the system. 230 */ 231 kobject_uevent(&foo->kobj, KOBJ_ADD); 232 233 return foo; 234 } 235 236 static void destroy_foo_obj(struct foo_obj *foo) 237 { 238 kobject_put(&foo->kobj); 239 } 240 241 static int __init example_init(void) 242 { 243 /* 244 * Create a kset with the name of "kset_example", 245 * located under /sys/kernel/ 246 */ 247 example_kset = kset_create_and_add("kset_example", NULL, kernel_kobj); 248 if (!example_kset) 249 return -ENOMEM; 250 251 /* 252 * Create three objects and register them with our kset 253 */ 254 foo_obj = create_foo_obj("foo"); 255 if (!foo_obj) 256 goto foo_error; 257 258 bar_obj = create_foo_obj("bar"); 259 if (!bar_obj) 260 goto bar_error; 261 262 baz_obj = create_foo_obj("baz"); 263 if (!baz_obj) 264 goto baz_error; 265 266 return 0; 267 268 baz_error: 269 destroy_foo_obj(bar_obj); 270 bar_error: 271 destroy_foo_obj(foo_obj); 272 foo_error: 273 kset_unregister(example_kset); 274 return -EINVAL; 275 } 276 277 static void __exit example_exit(void) 278 { 279 destroy_foo_obj(baz_obj); 280 destroy_foo_obj(bar_obj); 281 destroy_foo_obj(foo_obj); 282 kset_unregister(example_kset); 283 } 284 285 module_init(example_init); 286 module_exit(example_exit); 287 MODULE_LICENSE("GPL v2"); 288 MODULE_AUTHOR("Greg Kroah-Hartman <greg@kroah.com>"); 289