kobject: add sample code for how to use kobjects in a simple manner.

This is a simple kobject module, showing how to use kobj_attributes in
basic and more complex ways.

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

1 files changed, 137 insertions, 0 deletions

diff --git a/samples/kobject/kobject-example.c b/samples/kobject/kobject-example.c
new file mode 100644
index 000000000000..08d0d3ff3263
--- /dev/null
+++ b/samples/kobject/kobject-example.c
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+/*
+ * 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_put(example_kobj);
+
+        return retval;
+}
+
+static void example_exit(void)
+{
+        kobject_put(example_kobj);
+}
+
+module_init(example_init);
+module_exit(example_exit);
+MODULE_LICENSE("GPL");
+MODULE_AUTHOR("Greg Kroah-Hartman <greg@kroah.com>");