root/samples/kobject/kset-example.c

DEFINITIONS

1. foo_attr_show
2. foo_attr_store
3. foo_release
4. foo_show
5. foo_store
6. b_show
7. b_store
8. create_foo_obj
9. destroy_foo_obj
10. example_init
11. example_exit

/*
 * Sample kset and ktype implementation
 *
 * Copyright (C) 2004-2007 Greg Kroah-Hartman <greg@kroah.com>
 * Copyright (C) 2007 Novell Inc.
 *
 * Released under the GPL version 2 only.
 *
 */
#include <linux/kobject.h>
#include <linux/string.h>
#include <linux/sysfs.h>
#include <linux/module.h>
#include <linux/init.h>

/*
 * This module shows how to create a kset in sysfs called
 * /sys/kernel/kset-example
 * Then tree kobjects are created and assigned to this kset, "foo", "baz",
 * and "bar".  In those kobjects, attributes of the same name are also
 * created and if an integer is written to these files, it can be later
 * read out of it.
 */


/*
 * This is our "object" that we will create a few of and register them with
 * sysfs.
 */
struct foo_obj {
        struct kobject kobj;
        int foo;
        int baz;
        int bar;
};
#define to_foo_obj(x) container_of(x, struct foo_obj, kobj)

/* a custom attribute that works just for a struct foo_obj. */
struct foo_attribute {
        struct attribute attr;
        ssize_t (*show)(struct foo_obj *foo, struct foo_attribute *attr, char *buf);
        ssize_t (*store)(struct foo_obj *foo, struct foo_attribute *attr, const char *buf, size_t count);
};
#define to_foo_attr(x) container_of(x, struct foo_attribute, attr)

/*
 * The default show function that must be passed to sysfs.  This will be
 * called by sysfs for whenever a show function is called by the user on a
 * sysfs file associated with the kobjects we have registered.  We need to
 * transpose back from a "default" kobject to our custom struct foo_obj and
 * then call the show function for that specific object.
 */
static ssize_t foo_attr_show(struct kobject *kobj,
                             struct attribute *attr,
                             char *buf)
{
        struct foo_attribute *attribute;
        struct foo_obj *foo;

        attribute = to_foo_attr(attr);
        foo = to_foo_obj(kobj);

        if (!attribute->show)
                return -EIO;

        return attribute->show(foo, attribute, buf);
}

/*
 * Just like the default show function above, but this one is for when the
 * sysfs "store" is requested (when a value is written to a file.)
 */
static ssize_t foo_attr_store(struct kobject *kobj,
                              struct attribute *attr,
                              const char *buf, size_t len)
{
        struct foo_attribute *attribute;
        struct foo_obj *foo;

        attribute = to_foo_attr(attr);
        foo = to_foo_obj(kobj);

        if (!attribute->store)
                return -EIO;

        return attribute->store(foo, attribute, buf, len);
}

/* Our custom sysfs_ops that we will associate with our ktype later on */
static struct sysfs_ops foo_sysfs_ops = {
        .show = foo_attr_show,
        .store = foo_attr_store,
};

/*
 * The release function for our object.  This is REQUIRED by the kernel to
 * have.  We free the memory held in our object here.
 *
 * NEVER try to get away with just a "blank" release function to try to be
 * smarter than the kernel.  Turns out, no one ever is...
 */
static void foo_release(struct kobject *kobj)
{
        struct foo_obj *foo;

        foo = to_foo_obj(kobj);
        kfree(foo);
}

/*
 * The "foo" file where the .foo variable is read from and written to.
 */
static ssize_t foo_show(struct foo_obj *foo_obj, struct foo_attribute *attr,
                        char *buf)
{
        return sprintf(buf, "%d\n", foo_obj->foo);
}

static ssize_t foo_store(struct foo_obj *foo_obj, struct foo_attribute *attr,
                         const char *buf, size_t count)
{
        sscanf(buf, "%du", &foo_obj->foo);
        return count;
}

static struct foo_attribute foo_attribute =
        __ATTR(foo, 0666, foo_show, foo_store);

/*
 * More complex function where we determine which varible is being accessed by
 * looking at the attribute for the "baz" and "bar" files.
 */
static ssize_t b_show(struct foo_obj *foo_obj, struct foo_attribute *attr,
                      char *buf)
{
        int var;

        if (strcmp(attr->attr.name, "baz") == 0)
                var = foo_obj->baz;
        else
                var = foo_obj->bar;
        return sprintf(buf, "%d\n", var);
}

static ssize_t b_store(struct foo_obj *foo_obj, struct foo_attribute *attr,
                       const char *buf, size_t count)
{
        int var;

        sscanf(buf, "%du", &var);
        if (strcmp(attr->attr.name, "baz") == 0)
                foo_obj->baz = var;
        else
                foo_obj->bar = var;
        return count;
}

static struct foo_attribute baz_attribute =
        __ATTR(baz, 0666, b_show, b_store);
static struct foo_attribute bar_attribute =
        __ATTR(bar, 0666, b_show, b_store);

/*
 * Create a group of attributes so that we can create and destory them all
 * at once.
 */
static struct attribute *foo_default_attrs[] = {
        &foo_attribute.attr,
        &baz_attribute.attr,
        &bar_attribute.attr,
        NULL,   /* need to NULL terminate the list of attributes */
};

/*
 * Our own ktype for our kobjects.  Here we specify our sysfs ops, the
 * release function, and the set of default attributes we want created
 * whenever a kobject of this type is registered with the kernel.
 */
static struct kobj_type foo_ktype = {
        .sysfs_ops = &foo_sysfs_ops,
        .release = foo_release,
        .default_attrs = foo_default_attrs,
};

static struct kset *example_kset;
static struct foo_obj *foo_obj;
static struct foo_obj *bar_obj;
static struct foo_obj *baz_obj;

static struct foo_obj *create_foo_obj(const char *name)
{
        struct foo_obj *foo;
        int retval;

        /* allocate the memory for the whole object */
        foo = kzalloc(sizeof(*foo), GFP_KERNEL);
        if (!foo)
                return NULL;

        /*
         * As we have a kset for this kobject, we need to set it before calling
         * the kobject core.
         */
        foo->kobj.kset = example_kset;

        /*
         * Initialize and add the kobject to the kernel.  All the default files
         * will be created here.  As we have already specified a kset for this
         * kobject, we don't have to set a parent for the kobject, the kobject
         * will be placed beneath that kset automatically.
         */
        retval = kobject_init_and_add(&foo->kobj, &foo_ktype, NULL, "%s", name);
        if (retval) {
                kobject_put(&foo->kobj);
                return NULL;
        }

        /*
         * We are always responsible for sending the uevent that the kobject
         * was added to the system.
         */
        kobject_uevent(&foo->kobj, KOBJ_ADD);

        return foo;
}

static void destroy_foo_obj(struct foo_obj *foo)
{
        kobject_put(&foo->kobj);
}

static int example_init(void)
{
        /*
         * Create a kset with the name of "kset_example",
         * located under /sys/kernel/
         */
        example_kset = kset_create_and_add("kset_example", NULL, kernel_kobj);
        if (!example_kset)
                return -ENOMEM;

        /*
         * Create three objects and register them with our kset
         */
        foo_obj = create_foo_obj("foo");
        if (!foo_obj)
                goto foo_error;

        bar_obj = create_foo_obj("bar");
        if (!bar_obj)
                goto bar_error;

        baz_obj = create_foo_obj("baz");
        if (!baz_obj)
                goto baz_error;

        return 0;

baz_error:
        destroy_foo_obj(bar_obj);
bar_error:
        destroy_foo_obj(foo_obj);
foo_error:
        return -EINVAL;
}

static void example_exit(void)
{
        destroy_foo_obj(baz_obj);
        destroy_foo_obj(bar_obj);
        destroy_foo_obj(foo_obj);
        kset_unregister(example_kset);
}

module_init(example_init);
module_exit(example_exit);
MODULE_LICENSE("GPL");
MODULE_AUTHOR("Greg Kroah-Hartman <greg@kroah.com>");