samples/kobject/kset-example.c

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