forked from Minki/linux
docs: filesystems: convert sysfs.txt to ReST
- Add a SPDX header; - Add a document title; - Adjust document and section titles; - use :field: markup; - Some whitespace fixes and new line breaks; - Mark literal blocks as such; - Add it to filesystems/index.rst. Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org> Link: https://lore.kernel.org/r/5c480dcb467315b5df6e25372a65e473b585c36d.1581955849.git.mchehab+huawei@kernel.org Signed-off-by: Jonathan Corbet <corbet@lwn.net>
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Mauro Carvalho Chehab
Jonathan Corbet
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31771f45c8
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86beb97670
@ -87,5 +87,6 @@ Documentation for filesystem implementations.
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relay
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romfs
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squashfs
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sysfs
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virtiofs
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vfat
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@ -1,11 +1,15 @@
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.. SPDX-License-Identifier: GPL-2.0
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sysfs - _The_ filesystem for exporting kernel objects.
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=====================================================
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sysfs - _The_ filesystem for exporting kernel objects
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=====================================================
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Patrick Mochel <mochel@osdl.org>
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Mike Murphy <mamurph@cs.clemson.edu>
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Revised: 16 August 2011
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Original: 10 January 2003
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:Revised: 16 August 2011
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:Original: 10 January 2003
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What it is:
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@ -24,7 +28,7 @@ Using sysfs
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~~~~~~~~~~~
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sysfs is always compiled in if CONFIG_SYSFS is defined. You can access
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it by doing:
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it by doing::
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mount -t sysfs sysfs /sys
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@ -65,7 +69,7 @@ formatting of data is heavily frowned upon. Doing these things may get
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you publicly humiliated and your code rewritten without notice.
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An attribute definition is simply:
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An attribute definition is simply::
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struct attribute {
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char * name;
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@ -83,7 +87,7 @@ attribute. Subsystems are encouraged to define their own attribute
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structure and wrapper functions for adding and removing attributes for
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a specific object type.
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For example, the driver model defines struct device_attribute like:
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For example, the driver model defines struct device_attribute like::
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struct device_attribute {
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struct attribute attr;
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@ -96,16 +100,16 @@ struct device_attribute {
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int device_create_file(struct device *, const struct device_attribute *);
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void device_remove_file(struct device *, const struct device_attribute *);
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It also defines this helper for defining device attributes:
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It also defines this helper for defining device attributes::
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#define DEVICE_ATTR(_name, _mode, _show, _store) \
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struct device_attribute dev_attr_##_name = __ATTR(_name, _mode, _show, _store)
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For example, declaring
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For example, declaring::
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static DEVICE_ATTR(foo, S_IWUSR | S_IRUGO, show_foo, store_foo);
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is equivalent to doing:
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is equivalent to doing::
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static struct device_attribute dev_attr_foo = {
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.attr = {
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@ -127,15 +131,21 @@ readable. The above case could be shortened to:
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static struct device_attribute dev_attr_foo = __ATTR_RW(foo);
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the list of helpers available to define your wrapper function is:
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__ATTR_RO(name): assumes default name_show and mode 0444
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__ATTR_WO(name): assumes a name_store only and is restricted to mode
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__ATTR_RO(name):
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assumes default name_show and mode 0444
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__ATTR_WO(name):
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assumes a name_store only and is restricted to mode
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0200 that is root write access only.
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__ATTR_RO_MODE(name, mode): fore more restrictive RO access currently
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__ATTR_RO_MODE(name, mode):
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fore more restrictive RO access currently
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only use case is the EFI System Resource Table
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(see drivers/firmware/efi/esrt.c)
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__ATTR_RW(name): assumes default name_show, name_store and setting
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__ATTR_RW(name):
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assumes default name_show, name_store and setting
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mode to 0644.
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__ATTR_NULL: which sets the name to NULL and is used as end of list
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__ATTR_NULL:
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which sets the name to NULL and is used as end of list
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indicator (see: kernel/workqueue.c)
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Subsystem-Specific Callbacks
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@ -143,7 +153,7 @@ Subsystem-Specific Callbacks
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When a subsystem defines a new attribute type, it must implement a
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set of sysfs operations for forwarding read and write calls to the
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show and store methods of the attribute owners.
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show and store methods of the attribute owners::
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struct sysfs_ops {
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ssize_t (*show)(struct kobject *, struct attribute *, char *);
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@ -160,7 +170,7 @@ and struct attribute pointers to the appropriate pointer types, and
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calls the associated methods.
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To illustrate:
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To illustrate::
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#define to_dev(obj) container_of(obj, struct device, kobj)
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#define to_dev_attr(_attr) container_of(_attr, struct device_attribute, attr)
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@ -188,7 +198,7 @@ Reading/Writing Attribute Data
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To read or write attributes, show() or store() methods must be
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specified when declaring the attribute. The method types should be as
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simple as those defined for device attributes:
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simple as those defined for device attributes::
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ssize_t (*show)(struct device *dev, struct device_attribute *attr, char *buf);
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ssize_t (*store)(struct device *dev, struct device_attribute *attr,
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@ -251,7 +261,7 @@ Other notes:
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sure to have a way to check this, if necessary.
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A very simple (and naive) implementation of a device attribute is:
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A very simple (and naive) implementation of a device attribute is::
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static ssize_t show_name(struct device *dev, struct device_attribute *attr,
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char *buf)
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@ -280,7 +290,7 @@ Top Level Directory Layout
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The sysfs directory arrangement exposes the relationship of kernel
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data structures.
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The top level sysfs directory looks like:
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The top level sysfs directory looks like::
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block/
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bus/
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@ -296,7 +306,7 @@ directly to the internal kernel device tree, which is a hierarchy of
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struct device.
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bus/ contains flat directory layout of the various bus types in the
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kernel. Each bus's directory contains two subdirectories:
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kernel. Each bus's directory contains two subdirectories::
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devices/
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drivers/
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@ -331,9 +341,9 @@ Current Interfaces
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The following interface layers currently exist in sysfs:
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- devices (include/linux/device.h)
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----------------------------------
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Structure:
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devices (include/linux/device.h)
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--------------------------------
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Structure::
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struct device_attribute {
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struct attribute attr;
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@ -343,19 +353,19 @@ struct device_attribute {
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const char *buf, size_t count);
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};
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Declaring:
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Declaring::
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DEVICE_ATTR(_name, _mode, _show, _store);
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Creation/Removal:
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Creation/Removal::
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int device_create_file(struct device *dev, const struct device_attribute * attr);
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void device_remove_file(struct device *dev, const struct device_attribute * attr);
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- bus drivers (include/linux/device.h)
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--------------------------------------
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Structure:
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bus drivers (include/linux/device.h)
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------------------------------------
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Structure::
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struct bus_attribute {
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struct attribute attr;
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@ -363,22 +373,22 @@ struct bus_attribute {
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ssize_t (*store)(struct bus_type *, const char * buf, size_t count);
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};
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Declaring:
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Declaring::
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static BUS_ATTR_RW(name);
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static BUS_ATTR_RO(name);
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static BUS_ATTR_WO(name);
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Creation/Removal:
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Creation/Removal::
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int bus_create_file(struct bus_type *, struct bus_attribute *);
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void bus_remove_file(struct bus_type *, struct bus_attribute *);
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- device drivers (include/linux/device.h)
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-----------------------------------------
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device drivers (include/linux/device.h)
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---------------------------------------
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Structure:
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Structure::
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struct driver_attribute {
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struct attribute attr;
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@ -387,12 +397,12 @@ struct driver_attribute {
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size_t count);
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};
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Declaring:
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Declaring::
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DRIVER_ATTR_RO(_name)
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DRIVER_ATTR_RW(_name)
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Creation/Removal:
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Creation/Removal::
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int driver_create_file(struct device_driver *, const struct driver_attribute *);
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void driver_remove_file(struct device_driver *, const struct driver_attribute *);
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