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sysfs_emit() is preferred over sprintf() when formatting the value to be returned to user space in show() functions, because it knows about sysfs buffer specifics and has sanity checks. Signed-off-by: Nguyen Dinh Phi <phind.uet@gmail.com> Link: https://lore.kernel.org/r/20220303183618.1342358-1-phind.uet@gmail.com Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
144 lines
3.4 KiB
C
144 lines
3.4 KiB
C
// SPDX-License-Identifier: GPL-2.0
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/*
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* Sample kobject implementation
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*
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* Copyright (C) 2004-2007 Greg Kroah-Hartman <greg@kroah.com>
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* Copyright (C) 2007 Novell Inc.
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*/
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#include <linux/kobject.h>
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#include <linux/string.h>
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#include <linux/sysfs.h>
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#include <linux/module.h>
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#include <linux/init.h>
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/*
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* This module shows how to create a simple subdirectory in sysfs called
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* /sys/kernel/kobject-example In that directory, 3 files are created:
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* "foo", "baz", and "bar". If an integer is written to these files, it can be
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* later read out of it.
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*/
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static int foo;
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static int baz;
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static int bar;
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/*
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* The "foo" file where a static variable is read from and written to.
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*/
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static ssize_t foo_show(struct kobject *kobj, struct kobj_attribute *attr,
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char *buf)
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{
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return sysfs_emit(buf, "%d\n", foo);
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}
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static ssize_t foo_store(struct kobject *kobj, struct kobj_attribute *attr,
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const char *buf, size_t count)
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{
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int ret;
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ret = kstrtoint(buf, 10, &foo);
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if (ret < 0)
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return ret;
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return count;
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}
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/* Sysfs attributes cannot be world-writable. */
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static struct kobj_attribute foo_attribute =
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__ATTR(foo, 0664, foo_show, foo_store);
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/*
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* More complex function where we determine which variable is being accessed by
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* looking at the attribute for the "baz" and "bar" files.
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*/
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static ssize_t b_show(struct kobject *kobj, struct kobj_attribute *attr,
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char *buf)
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{
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int var;
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if (strcmp(attr->attr.name, "baz") == 0)
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var = baz;
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else
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var = bar;
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return sysfs_emit(buf, "%d\n", var);
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}
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static ssize_t b_store(struct kobject *kobj, struct kobj_attribute *attr,
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const char *buf, size_t count)
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{
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int var, ret;
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ret = kstrtoint(buf, 10, &var);
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if (ret < 0)
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return ret;
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if (strcmp(attr->attr.name, "baz") == 0)
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baz = var;
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else
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bar = var;
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return count;
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}
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static struct kobj_attribute baz_attribute =
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__ATTR(baz, 0664, b_show, b_store);
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static struct kobj_attribute bar_attribute =
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__ATTR(bar, 0664, b_show, b_store);
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/*
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* Create a group of attributes so that we can create and destroy them all
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* at once.
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*/
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static struct attribute *attrs[] = {
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&foo_attribute.attr,
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&baz_attribute.attr,
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&bar_attribute.attr,
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NULL, /* need to NULL terminate the list of attributes */
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};
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/*
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* An unnamed attribute group will put all of the attributes directly in
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* the kobject directory. If we specify a name, a subdirectory will be
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* created for the attributes with the directory being the name of the
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* attribute group.
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*/
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static struct attribute_group attr_group = {
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.attrs = attrs,
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};
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static struct kobject *example_kobj;
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static int __init example_init(void)
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{
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int retval;
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/*
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* Create a simple kobject with the name of "kobject_example",
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* located under /sys/kernel/
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*
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* As this is a simple directory, no uevent will be sent to
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* userspace. That is why this function should not be used for
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* any type of dynamic kobjects, where the name and number are
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* not known ahead of time.
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*/
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example_kobj = kobject_create_and_add("kobject_example", kernel_kobj);
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if (!example_kobj)
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return -ENOMEM;
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/* Create the files associated with this kobject */
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retval = sysfs_create_group(example_kobj, &attr_group);
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if (retval)
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kobject_put(example_kobj);
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return retval;
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}
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static void __exit example_exit(void)
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{
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kobject_put(example_kobj);
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}
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module_init(example_init);
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module_exit(example_exit);
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MODULE_LICENSE("GPL v2");
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MODULE_AUTHOR("Greg Kroah-Hartman <greg@kroah.com>");
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