// SPDX-License-Identifier: GPL-2.0 /* * Sample kset and ktype implementation * * Copyright (C) 2004-2007 Greg Kroah-Hartman <greg@kroah.com> * Copyright (C) 2007 Novell Inc. */ #include <linux/kobject.h> #include <linux/string.h> #include <linux/sysfs.h> #include <linux/slab.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 const 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 sysfs_emit(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) { int ret; ret = kstrtoint(buf, 10, &foo_obj->foo); if (ret < 0) return ret; return count; } /* Sysfs attributes cannot be world-writable. */ static struct foo_attribute foo_attribute = __ATTR(foo, 0664, foo_show, foo_store); /* * More complex function where we determine which variable 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 sysfs_emit(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, ret; ret = kstrtoint(buf, 10, &var); if (ret < 0) return ret; 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, 0664, b_show, b_store); static struct foo_attribute bar_attribute = __ATTR(bar, 0664, b_show, b_store); /* * Create a group of attributes so that we can create and destroy 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 */ }; ATTRIBUTE_GROUPS(foo_default); /* * 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_groups = foo_default_groups, }; 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 __init 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: kset_unregister(example_kset); return -EINVAL; } static void __exit 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 v2"); MODULE_AUTHOR("Greg Kroah-Hartman <greg@kroah.com>");