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    Subject[RFC] sample kobject implementation code

    /*
    * Sample kobject 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 simple subdirectory in sysfs called
    * /sys/kernel/kobject-example In that directory, 3 files are created:
    * "foo", "baz", and "bar". If an integer is written to these files, it can be
    * later read out of it.
    */

    static int foo;
    static int baz;
    static int bar;

    /*
    * The "foo" file where a static variable is read from and written to.
    */
    static ssize_t foo_show(struct kobject *kobj, struct kobj_attribute *attr,
    char *buf)
    {
    return sprintf(buf, "%d\n", foo);
    }

    static ssize_t foo_store(struct kobject *kobj, struct kobj_attribute *attr,
    const char *buf, size_t count)
    {
    sscanf(buf, "%du", &foo);
    return count;
    }

    static struct kobj_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 kobject *kobj, struct kobj_attribute *attr,
    char *buf)
    {
    int var;

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

    static ssize_t b_store(struct kobject *kobj, struct kobj_attribute *attr,
    const char *buf, size_t count)
    {
    int var;

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

    static struct kobj_attribute baz_attribute =
    __ATTR(baz, 0666, b_show, b_store);
    static struct kobj_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 *attrs[] = {
    &foo_attribute.attr,
    &baz_attribute.attr,
    &bar_attribute.attr,
    NULL, /* need to NULL terminate the list of attributes */
    };

    /*
    * An unnamed attribute group will put all of the attributes directly in
    * the kobject directory. If we specify a name, a subdirectory will be
    * created for the attributes with the directory being the name of the
    * attribute group.
    */
    static struct attribute_group attr_group = {
    .attrs = attrs,
    };

    static struct kobject *example_kobj;

    static int example_init(void)
    {
    int retval;

    /*
    * Create a simple kobject with the name of "kobject_example",
    * located under /sys/kernel/
    *
    * As this is a simple directory, no uevent will be sent to
    * userspace. That is why this function should not be used for
    * any type of dynamic kobjects, where the name and number are
    * not known ahead of time.
    */
    example_kobj = kobject_create_and_add("kobject_example", kernel_kobj);
    if (!example_kobj)
    return -ENOMEM;

    /* Create the files associated with this kobject */
    retval = sysfs_create_group(example_kobj, &attr_group);
    if (retval)
    kobject_unregister(example_kobj);

    return retval;
    }

    static void example_exit(void)
    {
    kobject_unregister(example_kobj);
    }

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


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