[PATCH 180/196] kobject: add sample code for how to use ksets/ktypes/kobjects

Greg Kroah-Hartman
2008-01-25T08:32:16Z

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>
---
samples/kobject/Makefile | 2 +-
samples/kobject/kset-example.c | 278 ++++++++++++++++++++++++++++++++++++++++
2 files changed, 279 insertions(+), 1 deletions(-)
create mode 100644 samples/kobject/kset-example.c

diff --git a/samples/kobject/Makefile b/samples/kobject/Makefile
index cce16e9..4a19420 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 0000000..b0a1b4f
--- /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>");
--
1.5.3.8