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 sscanf(buf, "%du", &foo_obj->foo); 124 return count; 125 } 126 127 static struct foo_attribute foo_attribute = 128 __ATTR(foo, 0666, foo_show, foo_store); 129 130 /* 131 * More complex function where we determine which variable is being accessed by 132 * looking at the attribute for the "baz" and "bar" files. 133 */ 134 static ssize_t b_show(struct foo_obj *foo_obj, struct foo_attribute *attr, 135 char *buf) 136 { 137 int var; 138 139 if (strcmp(attr->attr.name, "baz") == 0) 140 var = foo_obj->baz; 141 else 142 var = foo_obj->bar; 143 return sprintf(buf, "%d\n", var); 144 } 145 146 static ssize_t b_store(struct foo_obj *foo_obj, struct foo_attribute *attr, 147 const char *buf, size_t count) 148 { 149 int var; 150 151 sscanf(buf, "%du", &var); 152 if (strcmp(attr->attr.name, "baz") == 0) 153 foo_obj->baz = var; 154 else 155 foo_obj->bar = var; 156 return count; 157 } 158 159 static struct foo_attribute baz_attribute = 160 __ATTR(baz, 0666, b_show, b_store); 161 static struct foo_attribute bar_attribute = 162 __ATTR(bar, 0666, b_show, b_store); 163 164 /* 165 * Create a group of attributes so that we can create and destroy them all 166 * at once. 167 */ 168 static struct attribute *foo_default_attrs[] = { 169 &foo_attribute.attr, 170 &baz_attribute.attr, 171 &bar_attribute.attr, 172 NULL, /* need to NULL terminate the list of attributes */ 173 }; 174 175 /* 176 * Our own ktype for our kobjects. Here we specify our sysfs ops, the 177 * release function, and the set of default attributes we want created 178 * whenever a kobject of this type is registered with the kernel. 179 */ 180 static struct kobj_type foo_ktype = { 181 .sysfs_ops = &foo_sysfs_ops, 182 .release = foo_release, 183 .default_attrs = foo_default_attrs, 184 }; 185 186 static struct kset *example_kset; 187 static struct foo_obj *foo_obj; 188 static struct foo_obj *bar_obj; 189 static struct foo_obj *baz_obj; 190 191 static struct foo_obj *create_foo_obj(const char *name) 192 { 193 struct foo_obj *foo; 194 int retval; 195 196 /* allocate the memory for the whole object */ 197 foo = kzalloc(sizeof(*foo), GFP_KERNEL); 198 if (!foo) 199 return NULL; 200 201 /* 202 * As we have a kset for this kobject, we need to set it before calling 203 * the kobject core. 204 */ 205 foo->kobj.kset = example_kset; 206 207 /* 208 * Initialize and add the kobject to the kernel. All the default files 209 * will be created here. As we have already specified a kset for this 210 * kobject, we don't have to set a parent for the kobject, the kobject 211 * will be placed beneath that kset automatically. 212 */ 213 retval = kobject_init_and_add(&foo->kobj, &foo_ktype, NULL, "%s", name); 214 if (retval) { 215 kobject_put(&foo->kobj); 216 return NULL; 217 } 218 219 /* 220 * We are always responsible for sending the uevent that the kobject 221 * was added to the system. 222 */ 223 kobject_uevent(&foo->kobj, KOBJ_ADD); 224 225 return foo; 226 } 227 228 static void destroy_foo_obj(struct foo_obj *foo) 229 { 230 kobject_put(&foo->kobj); 231 } 232 233 static int __init example_init(void) 234 { 235 /* 236 * Create a kset with the name of "kset_example", 237 * located under /sys/kernel/ 238 */ 239 example_kset = kset_create_and_add("kset_example", NULL, kernel_kobj); 240 if (!example_kset) 241 return -ENOMEM; 242 243 /* 244 * Create three objects and register them with our kset 245 */ 246 foo_obj = create_foo_obj("foo"); 247 if (!foo_obj) 248 goto foo_error; 249 250 bar_obj = create_foo_obj("bar"); 251 if (!bar_obj) 252 goto bar_error; 253 254 baz_obj = create_foo_obj("baz"); 255 if (!baz_obj) 256 goto baz_error; 257 258 return 0; 259 260 baz_error: 261 destroy_foo_obj(bar_obj); 262 bar_error: 263 destroy_foo_obj(foo_obj); 264 foo_error: 265 kset_unregister(example_kset); 266 return -EINVAL; 267 } 268 269 static void __exit example_exit(void) 270 { 271 destroy_foo_obj(baz_obj); 272 destroy_foo_obj(bar_obj); 273 destroy_foo_obj(foo_obj); 274 kset_unregister(example_kset); 275 } 276 277 module_init(example_init); 278 module_exit(example_exit); 279 MODULE_LICENSE("GPL"); 280 MODULE_AUTHOR("Greg Kroah-Hartman <greg@kroah.com>"); 281