kobject: add sample code for how to use ksets/ktypes/kobjects

This is a more complex example showing how to create a kset and a ktype
and some default attributes for a group of kobjects.

Cc: Kay Sievers <kay.sievers@vrfy.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

2 files changed, 279 insertions, 1 deletions

diff --git a/samples/kobject/Makefile b/samples/kobject/Makefile
index cce16e99fde..4a194203c98 100644
--- a/samples/kobject/Makefile
+++ b/samples/kobject/Makefile
@@ -1 +1 @@
-obj-$(CONFIG_SAMPLE_KOBJECT) += kobject-example.o
+obj-$(CONFIG_SAMPLE_KOBJECT) += kobject-example.o kset-example.o
diff --git a/samples/kobject/kset-example.c b/samples/kobject/kset-example.c
new file mode 100644
index 00000000000..b0a1b4fe658
--- /dev/null
+++ b/samples/kobject/kset-example.c
@@ -0,0 +1,278 @@
+/*
+ * 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) {
+                kfree(foo);
+                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>");