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/module.h> 14 #include <linux/init.h> 15 16 /* 17 * This module shows how to create a kset in sysfs called 18 * /sys/kernel/kset-example 19 * Then tree kobjects are created and assigned to this kset, "foo", "baz", 20 * and "bar". In those kobjects, attributes of the same name are also 21 * created and if an integer is written to these files, it can be later 22 * read out of it. 23 */ 24 25 26 /* 27 * This is our "object" that we will create a few of and register them with 28 * sysfs. 29 */ 30 struct foo_obj { 31 struct kobject kobj; 32 int foo; 33 int baz; 34 int bar; 35 }; 36 #define to_foo_obj(x) container_of(x, struct foo_obj, kobj) 37 38 /* a custom attribute that works just for a struct foo_obj. */ 39 struct foo_attribute { 40 struct attribute attr; 41 ssize_t (*show)(struct foo_obj *foo, struct foo_attribute *attr, char *buf); 42 ssize_t (*store)(struct foo_obj *foo, struct foo_attribute *attr, const char *buf, size_t count); 43 }; 44 #define to_foo_attr(x) container_of(x, struct foo_attribute, attr) 45 46 /* 47 * The default show function that must be passed to sysfs. This will be 48 * called by sysfs for whenever a show function is called by the user on a 49 * sysfs file associated with the kobjects we have registered. We need to 50 * transpose back from a "default" kobject to our custom struct foo_obj and 51 * then call the show function for that specific object. 52 */ 53 static ssize_t foo_attr_show(struct kobject *kobj, 54 struct attribute *attr, 55 char *buf) 56 { 57 struct foo_attribute *attribute; 58 struct foo_obj *foo; 59 60 attribute = to_foo_attr(attr); 61 foo = to_foo_obj(kobj); 62 63 if (!attribute->show) 64 return -EIO; 65 66 return attribute->show(foo, attribute, buf); 67 } 68 69 /* 70 * Just like the default show function above, but this one is for when the 71 * sysfs "store" is requested (when a value is written to a file.) 72 */ 73 static ssize_t foo_attr_store(struct kobject *kobj, 74 struct attribute *attr, 75 const char *buf, size_t len) 76 { 77 struct foo_attribute *attribute; 78 struct foo_obj *foo; 79 80 attribute = to_foo_attr(attr); 81 foo = to_foo_obj(kobj); 82 83 if (!attribute->store) 84 return -EIO; 85 86 return attribute->store(foo, attribute, buf, len); 87 } 88 89 /* Our custom sysfs_ops that we will associate with our ktype later on */ 90 static struct sysfs_ops foo_sysfs_ops = { 91 .show = foo_attr_show, 92 .store = foo_attr_store, 93 }; 94 95 /* 96 * The release function for our object. This is REQUIRED by the kernel to 97 * have. We free the memory held in our object here. 98 * 99 * NEVER try to get away with just a "blank" release function to try to be 100 * smarter than the kernel. Turns out, no one ever is... 101 */ 102 static void foo_release(struct kobject *kobj) 103 { 104 struct foo_obj *foo; 105 106 foo = to_foo_obj(kobj); 107 kfree(foo); 108 } 109 110 /* 111 * The "foo" file where the .foo variable is read from and written to. 112 */ 113 static ssize_t foo_show(struct foo_obj *foo_obj, struct foo_attribute *attr, 114 char *buf) 115 { 116 return sprintf(buf, "%d\n", foo_obj->foo); 117 } 118 119 static ssize_t foo_store(struct foo_obj *foo_obj, struct foo_attribute *attr, 120 const char *buf, size_t count) 121 { 122 sscanf(buf, "%du", &foo_obj->foo); 123 return count; 124 } 125 126 static struct foo_attribute foo_attribute = 127 __ATTR(foo, 0666, foo_show, foo_store); 128 129 /* 130 * More complex function where we determine which varible is being accessed by 131 * looking at the attribute for the "baz" and "bar" files. 132 */ 133 static ssize_t b_show(struct foo_obj *foo_obj, struct foo_attribute *attr, 134 char *buf) 135 { 136 int var; 137 138 if (strcmp(attr->attr.name, "baz") == 0) 139 var = foo_obj->baz; 140 else 141 var = foo_obj->bar; 142 return sprintf(buf, "%d\n", var); 143 } 144 145 static ssize_t b_store(struct foo_obj *foo_obj, struct foo_attribute *attr, 146 const char *buf, size_t count) 147 { 148 int var; 149 150 sscanf(buf, "%du", &var); 151 if (strcmp(attr->attr.name, "baz") == 0) 152 foo_obj->baz = var; 153 else 154 foo_obj->bar = var; 155 return count; 156 } 157 158 static struct foo_attribute baz_attribute = 159 __ATTR(baz, 0666, b_show, b_store); 160 static struct foo_attribute bar_attribute = 161 __ATTR(bar, 0666, b_show, b_store); 162 163 /* 164 * Create a group of attributes so that we can create and destory them all 165 * at once. 166 */ 167 static struct attribute *foo_default_attrs[] = { 168 &foo_attribute.attr, 169 &baz_attribute.attr, 170 &bar_attribute.attr, 171 NULL, /* need to NULL terminate the list of attributes */ 172 }; 173 174 /* 175 * Our own ktype for our kobjects. Here we specify our sysfs ops, the 176 * release function, and the set of default attributes we want created 177 * whenever a kobject of this type is registered with the kernel. 178 */ 179 static struct kobj_type foo_ktype = { 180 .sysfs_ops = &foo_sysfs_ops, 181 .release = foo_release, 182 .default_attrs = foo_default_attrs, 183 }; 184 185 static struct kset *example_kset; 186 static struct foo_obj *foo_obj; 187 static struct foo_obj *bar_obj; 188 static struct foo_obj *baz_obj; 189 190 static struct foo_obj *create_foo_obj(const char *name) 191 { 192 struct foo_obj *foo; 193 int retval; 194 195 /* allocate the memory for the whole object */ 196 foo = kzalloc(sizeof(*foo), GFP_KERNEL); 197 if (!foo) 198 return NULL; 199 200 /* 201 * As we have a kset for this kobject, we need to set it before calling 202 * the kobject core. 203 */ 204 foo->kobj.kset = example_kset; 205 206 /* 207 * Initialize and add the kobject to the kernel. All the default files 208 * will be created here. As we have already specified a kset for this 209 * kobject, we don't have to set a parent for the kobject, the kobject 210 * will be placed beneath that kset automatically. 211 */ 212 retval = kobject_init_and_add(&foo->kobj, &foo_ktype, NULL, "%s", name); 213 if (retval) { 214 kfree(foo); 215 return NULL; 216 } 217 218 /* 219 * We are always responsible for sending the uevent that the kobject 220 * was added to the system. 221 */ 222 kobject_uevent(&foo->kobj, KOBJ_ADD); 223 224 return foo; 225 } 226 227 static void destroy_foo_obj(struct foo_obj *foo) 228 { 229 kobject_put(&foo->kobj); 230 } 231 232 static int example_init(void) 233 { 234 /* 235 * Create a kset with the name of "kset_example", 236 * located under /sys/kernel/ 237 */ 238 example_kset = kset_create_and_add("kset_example", NULL, kernel_kobj); 239 if (!example_kset) 240 return -ENOMEM; 241 242 /* 243 * Create three objects and register them with our kset 244 */ 245 foo_obj = create_foo_obj("foo"); 246 if (!foo_obj) 247 goto foo_error; 248 249 bar_obj = create_foo_obj("bar"); 250 if (!bar_obj) 251 goto bar_error; 252 253 baz_obj = create_foo_obj("baz"); 254 if (!baz_obj) 255 goto baz_error; 256 257 return 0; 258 259 baz_error: 260 destroy_foo_obj(bar_obj); 261 bar_error: 262 destroy_foo_obj(foo_obj); 263 foo_error: 264 return -EINVAL; 265 } 266 267 static void example_exit(void) 268 { 269 destroy_foo_obj(baz_obj); 270 destroy_foo_obj(bar_obj); 271 destroy_foo_obj(foo_obj); 272 kset_unregister(example_kset); 273 } 274 275 module_init(example_init); 276 module_exit(example_exit); 277 MODULE_LICENSE("GPL"); 278 MODULE_AUTHOR("Greg Kroah-Hartman <greg@kroah.com>"); 279