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