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System Utilities sysfs Library - libsysfs
=========================================
Version: 2.0.0
November 25, 2005
Contents
--------
1. Introduction
2. Requirements
3. Definitions
4. Overview
5. Data Structures
5.1 Attribute Data Structure
5.2 Bus Data Structure
5.3 Class Data Structures
5.4 Device Data Structure
5.5 Driver Data Structure
5.6 Module Data Structure
6. Functions
6.1 Calling Conventions in Libsysfs
6.2 Utility Functions
6.3 Attribute Functions
6.4 Bus Functions
6.5 Class Functions
6.6 Device Functions
6.7 Driver Functions
6.8 Module functions
7. Dlists
7.1 Navigating a dlist
7.2 Custom sorting using dlist_sort_custom()
7.3 Custom filtering and sorting using dlist_filter_sort()
8. Usage
9. Testsuite
10. Conclusion
1. Introduction
---------------
Libsysfs' purpose is to provide a consistent and stable interface for
querying system device information exposed through the sysfs filesystem.
The library implements functions for querying filesystem information,
such as reading directories and files. It also contains routines for
working with buses, classes, and the device tree.
2. Requirements
---------------
The library must satisfy the following requirements:
- It must provide a stable programming interfaces that applications can
be built upon.
- It must provide functions to retrieve device Vital Product Data (VPD)
information for Error Log Analysis (ELA) support. ELA will provide
device driver and device bus address information.
- It must provide access to all system devices and information exposed
by sysfs.
- It must provide a function to find sysfs' current mount point.
- It must provide a function for udev to retrieve a device's major and
minor numbers.
3. Definitions
--------------
- sysfs: Sysfs is a virtual filesystem in 2.5+ Linux kernels that
presents a hierarchical representation of all system physical and
virtual devices. It presents system devices by bus, by class, and
by topology. Callbacks to device drivers are exposed as files in
device directories. Sysfs, for all purposes, is our tree of system
devices. For more information, please see:
http://www.kernel.org/pub/linux/kernel/people/mochel/doc/
- udev: Udev is Greg Kroah-Hartman's User Space implementation of devfs.
Udev creates /dev nodes for devices upon Hotplug events. The Hotplug
event provides udev with a sysfs directory location of the device. Udev
must use that directory to grab device's major and minor number, which it
will use to create the /dev node. For more information, please see:
http://www.kernel.org/pub/linux/utils/kernel/hotplug/
Udev provides persistent device naming based on a set of user specified
rules. The rules a device name is based on could one or a combination of a
number of parameters such as the bus the device is on, the serial number
of the device (in case of USB), the vendor name (in case of SCSI) and so
on. Udev uses Libsysfs to retrieve relevent information to appropriately
name devices.
4. Overview
-----------
Libsysfs grew from a common need. There are several applications under
development that need access to sysfs and system devices. Udev, on a
hotplug event, must take a sysfs device path and create a /dev node. Our
diagnostic client needs to list all system devices. Finally, our Error
Log Analysis piece is required to retrieve VPD information for a
failing device. We divided to create a single library interface rather
than having these separate applications create their own accesses to
sysfs involving reading directories and files.
Libsysfs will also provide stability for applications to be built upon. Sysfs
currently doesn't enforce any standards for callback or file names. File
names change depending on bus or class. Sysfs is also changing, it is
currently being developed. Libsysfs will provide a stable interface to
applications while allowing sysfs to change underneath it.
Like sysfs, the library will provide devices to applications by bus, by
class, and by topology. The library will function similar to directories
and files that lie underneath it. To query a device on a PCI bus, one would
"open" the bus to scan or read devices and "close" the bus when
completed. Besides supplying functions to retrieve devices, the library
will also provide some utility functions like getting sysfs mount point.
A paper on Libsysfs was presented at Linux.Conf.Au 2004 (Adelaide, January
2004). The paper is available online at:
http://oss.software.ibm.com/linux/papers/libsysfs/libsysfs-linuxconfau2004.pdf
5. Data Structures
------------------
Libsysfs will classify system devices following sysfs' example, dividing
them by bus, class, and devices. The library presents this information
generically. It doesn't, for example, differentiate between PCI and USB
buses. Device attributes are presented with values as they are exposed
by sysfs, the values are not formatted.
The library will provide standard definitions for working with sysfs
and devices, here's some examples:
#define SYSFS_FSTYPE_NAME "sysfs"
#define SYSFS_PROC_MNTS "/proc/mounts"
#define SYSFS_BUS_NAME "bus"
#define SYSFS_CLASS_NAME "class"
#define SYSFS_BLOCK_NAME "block"
#define SYSFS_DEVICES_NAME "devices"
#define SYSFS_DRIVERS_NAME "drivers"
#define SYSFS_NAME_ATTRIBUTE "name"
#define SYSFS_MOD_PARM_NAME "parameters"
#define SYSFS_MOD_SECT_NAME "sections"
#define SYSFS_UNKNOWN "unknown"
#define SYSFS_PATH_ENV "SYSFS_PATH"
The library uses some definitions to mark maximum size of a sysfs name or
path length:
#define SYSFS_PATH_MAX 256
#define SYSFS_NAME_LEN 64
#define SYSFS_BUS_ID_SIZE 32
NOTE:
a. As of release 0.4.0 of sysfsutils, a number of changes have been
made so that the dlists and "directory" references in all libsysfs's
structures are not populated until such time that it is absolutely
necessary. Hence, these elements may not contain valid data at all
times (as was the case before).
b. As of release 1.0.0 of sysfsutils, all dlists in the library are
sorted in alphabetical order. It is now a requirement that the
"name" and "path" be the first two elements of all libsysfs
structures.
c. There has been a major overhaul with 2.0.0 release of sysfsutils.
We now have a much leaner and meaner library without the overhead
of the sysfs_directory and related structures. The API list has
also been pruned to contain the most frequently used calls and
the lists are not populated all at once. This has lead to enormous
speed improvements as well as reduction in the number of system
calls.
5.1 Attribute Data Structure
-------------------------------------------
The library implements structure to represent sysfs files.
A file in sysfs represents a device or driver attribute. Attributes can be
read only, write only, or read and write. File data can be ASCII and
binary. The library has the following structure to represent files:
struct sysfs_attribute {
char name[SYSFS_NAME_LEN];
char path[SYSFS_PATH_MAX];
char *value;
unsigned short len; /* value length */
enum sysfs_attribute_method method; /* show and store */
};
Path represents the file/attribute's full path. Value is used when reading
from or writing to an attribute. "len" is the length of data in "value".
Method is an enum for defining if the attribute supports show(read) and/or
store(write).
5.2 Bus Data Structure
----------------------
All buses look similar in sysfs including lists of devices and drivers,
therefore we use the following structure to represent all sysfs buses:
struct sysfs_bus {
char name[SYSFS_NAME_LEN];
char path[SYSFS_PATH_MAX];
struct dlist *attrlist;
/* Private: for internal use only */
struct dlist *drivers;
struct dlist *devices;
};
The sysfs_bus structure contains the bus "name", while the "path" to bus
directory is also stored. It also contains lists of devices on the bus
and drivers that are registered on it.
5.3 Class Data Structures
-------------------------
The library uses two data structures to represent classes in sysfs. Sysfs
classes contains a class directory like "net" or "scsi_host" and then
class devices like "eth0", "lo", or "eth1" for the "net" class.
struct sysfs_class {
char name[SYSFS_NAME_LEN];
char path[SYSFS_PATH_MAX];
struct dlist *attrlist;
/* Private: for internal use only */
struct dlist *devices;
};
The sysfs_class represents device classes in sysfs like "net". It contains
the class "name", "path" to the class and a list of class devices
struct sysfs_class_device {
char name[SYSFS_NAME_LEN];
char path[SYSFS_PATH_MAX];
struct dlist *attrlist;
char classname[SYSFS_NAME_LEN];
/* Private: for internal use only */
struct sysfs_class_device *parent;
struct sysfs_device *sysdevice; /* NULL if virtual */
};
A class device isn't the same as a sysfs_device, it's specific to the class in
which it belongs. The class device structure contains the name of the class
the class device belongs to and its sysfs_device reference. It also contains
the name of the class device - like "eth0", its parent (if present).
5.4 Device Data Structure
-------------------------
The sysfs_device structure represents a system device that's exposed
in sysfs under the /sys/devices directory structure.
struct sysfs_device {
char name[SYSFS_NAME_LEN];
char path[SYSFS_PATH_MAX];
struct dlist *attrlist;
char bus_id[SYSFS_NAME_LEN];
char bus[SYSFS_NAME_LEN];
char driver_name[SYSFS_NAME_LEN];
/* Private: for internal use only */
struct sysfs_device *parent;
struct dlist *children;
};
The sysfs_device structure contains a "parent" pointer, a list of child
devices, if any, device's directory, its bus id - which is the name of
device's directory, the bus name on which this device is registered and
its driver name. The device structure also contains the absolute path
to the device.
5.5 Driver Data Structure
-------------------------
The sysfs_driver structure represents a device driver.
struct sysfs_driver {
char name[SYSFS_NAME_LEN];
char path[SYSFS_PATH_MAX];
struct dlist *attrlist;
char bus[SYSFS_NAME_LEN];
/* Private: for internal use only */
struct sysfs_module *module;
struct dlist *devices;
};
The sysfs_driver structure contains a list of devices that use this driver,
the name of the driver, the module it is using and a list of attributes
for the driver.
5.6 Module Data Structure
-------------------------
The sysfs_module structure represents the module loaded in the system.
struct sysfs_module {
char name[SYSFS_NAME_LEN];
char path[SYSFS_PATH_MAX];
struct dlist *attrlist;
struct dlist *parmlist;
struct dlist *sections;
};
The sysfs_module structure contains a list of attributes, parameters and
sections used by the corresponding module. It also contains name of the
module, its path. The following functions can be used to retrive the
information related to the module.
struct dlist *sysfs_get_module_parms(struct sysfs_module *module)
struct dlist *sysfs_get_module_sections(struct sysfs_module *module)
struct dlist *sysfs_get_module_attributes(struct sysfs_module *module)
6. Functions
------------
Libsysfs will provide functions to access system devices by bus, by class,
and by device. Functions will act like accessing directories and files,
using "open" and "close". Open returns a structure and close is used
to clean that structure up.
6.1 Calling Conventions in Libsysfs
-----------------------------------
Libsysfs uses a simple API calling convention. APIs are classified to be
one of "open", "get", "close" types. The convention is as follows:
a. All "open" APIs have a corresponding "close" API.
b. References obtained using "get" calls should not be closed
explicitly.
c. All "opened" references have to be closed with a call to
their corresponding "close" call. This takes care of
freeing structure references obtained with "get" calls.
6.2 Utility Functions
---------------------
The library will provide a few utility functions for working with sysfs.
-------------------------------------------------------------------------------
Name: sysfs_get_mnt_path
Description: Function finds the mount path for filesystem type "sysfs".
Arguments: char *mnt_path Mount path buffer
size_t len Size of mount path buffer
Returns: Zero with success.
-1 with error. Errno will be set with error:
- EINVAL for invalid argument, if buffer is NULL or
if len is zero
Prototype: sysfs_get_mnt_path(char *mnt_path, size_t len);
-------------------------------------------------------------------------------
-------------------------------------------------------------------------------
Name: sysfs_get_name_from_path
Description: Function returns the last directory or file name from the
included path.
Arguments: const char *path Path to parse name from
char *name Buffer to put parsed name into
size_t *len Size of name buffer
Returns: 0 with success.
-1 on Error. Errno will be set with error, returning
- EINVAL for invalid arguments
Prototype: int sysfs_get_name_from_path(const char *path,
char *name, size_t *len)
-------------------------------------------------------------------------------
-------------------------------------------------------------------------------
Name: sysfs_get_link
Description: Sysfs readlink function, reads the link at supplied path
and returns its target path.
Arguments: const char *path Link's path
char *target Buffer to place link's target
size_t len Size of target buffer
Returns: 0 with success
-1 with error. Errno will be set with error, returning
- EINVAL for invalid arguments
Prototype: int sysfs_get_link(const char *path, char *target, size_t len)
-------------------------------------------------------------------------------
-------------------------------------------------------------------------------
Name: sysfs_close_list
Description: Closes a given dlist. This can be used as a generic list close
routine.
Arguments: struct dlist *list List to be closed
Prototype: void sysfs_close_list(struct dlist *list)
-------------------------------------------------------------------------------
-------------------------------------------------------------------------------
Name: sysfs_path_is_dir
Description: Utility function to verify if a given path is to a directory.
Arguments: const char *path Path to verify
Returns: 0 on success, 1 on error
- EINVAL for invalid arguments
Prototype: int sysfs_path_is_dir(const char *path)
-------------------------------------------------------------------------------
-------------------------------------------------------------------------------
Name: sysfs_path_is_file
Description: Utility function to verify if a given path is to a file.
Arguments: const char *path Path to verify
Returns: 0 on success, 1 on error
- EINVAL for invalid arguments
Prototype: int sysfs_path_is_file(const char *path)
-------------------------------------------------------------------------------
-------------------------------------------------------------------------------
Name: sysfs_path_is_link
Description: Utility function to verify if a given path is to a link.
Arguments: const char *path Path to verify
Returns: 0 on success, 1 on error
- EINVAL for invalid arguments
Prototype: int sysfs_path_is_link(const char *path)
-------------------------------------------------------------------------------
-------------------------------------------------------------------------------
Name: sysfs_open_directory_list
Description: Utility function to get list of all directories under path.
Arguments: const char *path Path to read
Returns: Directory list on success, NULL on error
Prototype: struct dlist *sysfs_open_directory_list(const char *path)
-------------------------------------------------------------------------------
6.3 Attribute Functions
------------------------
Libsysfs provides a set of functions to open, read, and close attributes in sysfs. These functions mirror their filesystem function counterparts.
Along with the usual open, read, and close functions, libsysfs provides
a couple other functions for accessing attribute values.
-------------------------------------------------------------------------------
Name: sysfs_open_attribute
Description: Opens up a file in sysfs and creates a sysfs_attribute
structure. File isn't read with this function.
Arguments: const char *path File/Attribute's path
Returns: struct sysfs_attribute * with success.
NULL with error. Errno will be set with error, returning
- EINVAL for invalid arguments
Prototype: struct sysfs_attribute *sysfs_open_attribute(const char *path)
-------------------------------------------------------------------------------
-------------------------------------------------------------------------------
Name: sysfs_close_attribute
Description: Cleans up and closes sysfs_attribute structure.
Arguments: struct sysfs_attribute *sysattr Attribute to close
Prototype: void sysfs_close_attribute(struct sysfs_attribute *sysattr)
-------------------------------------------------------------------------------
-------------------------------------------------------------------------------
Name: sysfs_read_attribute
Description: Reads the supplied attribute. Since the maximum transfer
from a sysfs attribute is a pagesize, function reads in
up to a page from the file and stores it in the "value"
field in the attribute.
Arguments: struct sysfs_attribute *sysattr Attribute to read
Returns: 0 with success.
-1 with error. Errno will be set with error, returning
- EINVAL for invalid arguments
Prototype: int sysfs_read_attribute(struct sysfs_attribute *sysattr)
-------------------------------------------------------------------------------
-------------------------------------------------------------------------------
Name: sysfs_write_attribute
Description: Writes to the supplied attribute. Function validates if the
given attribute is writable, and writes the new value to the
attribute. Value to write as well as its length is user
supplied. In case the length written is not equal to the
length requested to be written, the original value is
restored and an error is returned.
Arguments: struct sysfs_attribute *sysattr Attribute to write to
const char *new_value sysattr's new value
size_t len Length of "new_value"
Returns: 0 with success.
-1 with error. Errno will be set with error, returning
- EINVAL for invalid arguments
Prototype: int sysfs_write_attribute(struct sysfs_attribute *sysattr,
const char *new_value, size_t len)
-------------------------------------------------------------------------------
6.4 Bus Functions
-----------------
The library provides a functions for viewing buses represented in sysfs.
The sysfs_open_bus opens a bus in the /sys/bus directory, such as "pci",
"usb", or "scsi". The open command returns a sysfs_bus structure that
contains a list of the bus' devices. The sysfs_close_bus function is
used to clean up the bus structure. Given a device or a driver,
functions are provided to determine what bus they are on.
-------------------------------------------------------------------------------
Name: sysfs_open_bus
Description: Function opens up one of the buses represented in sysfs in
the /sys/bus directory. It returns a sysfs_bus structure
that includes a list of bus devices and drivers.
Arguments: const char *name Bus name to open, like "pci"...
Returns: struct sysfs_bus * with success
NULL with error. Errno will be set with error, returning
- EINVAL for invalid arguments
Prototype: struct sysfs_bus *sysfs_open_bus(const char *name)
-------------------------------------------------------------------------------
-------------------------------------------------------------------------------
Name: sysfs_close_bus
Description: Function closes up the sysfs_bus structure including its
devices, and drivers and the list of attributes.
Arguments: sysfs_bus *bus Bus structure to close
Prototype: void sysfs_close_bus(struct sysfs_bus *bus)
-------------------------------------------------------------------------------
-------------------------------------------------------------------------------
Name: sysfs_get_bus_devices
Description: Function returns a list of devices that are registered with
this bus.
Arguments: struct sysfs_bus *bus Bus whose devices list to return
Returns: struct dlist * of sysfs_devices on success
NULL with error. Errno will be sent with error, returning
- EINVAL for invalid arguments
Prototype: struct dlist *sysfs_get_bus_devices(struct sysfs_bus *bus)
-------------------------------------------------------------------------------
-------------------------------------------------------------------------------
Name: sysfs_get_bus_drivers
Description: Function returns a list of drivers that are registered with
this bus.
Arguments: struct sysfs_bus *bus Bus whose drivers list to return
Returns: struct dlist * of sysfs_drivers on success
NULL with error. Errno will be sent with error, returning
- EINVAL for invalid arguments
Prototype: struct dlist *sysfs_get_bus_drivers(struct sysfs_bus *bus)
-------------------------------------------------------------------------------
-------------------------------------------------------------------------------
Name: sysfs_get_bus_device
Description: Function takes a sysfs_bus structure(obtained on a successful
return from a sysfs_open_bus() call) and looks for the given
device on this bus. On success, it returns a sysfs_device
structure corresponding to the device.
Arguments: struct sysfs_bus *bus Bus structure on which to search
char *id Device to look for
Returns: struct sysfs_device * with success
NULL with error. Errno will be set with error, returning
- EINVAL for invalid arguments
Prototype: struct sysfs_device *sysfs_get_bus_device
(struct sysfs_bus *bus, char *id)
-------------------------------------------------------------------------------
-------------------------------------------------------------------------------
Name: sysfs_get_bus_driver
Description: Function takes a sysfs_bus structure (obtained on a successful
return from a sysfs_open_bus() call) and looks for the given
driver on this bus. On success, it returns a sysfs_driver
structure corresponding to the driver.
Arguments: struct sysfs_bus *bus Bus structure on which to search
char *drvname Driver to look for
Returns: struct sysfs_driver * with success
NULL with error. Errno will be set with error, returning
- EINVAL for invalid arguments
Prototype: struct sysfs_device *sysfs_get_bus_driver
(struct sysfs_bus *bus, char *drvname)
-------------------------------------------------------------------------------
6.5 Class Functions
-------------------
Libsysfs provides functions to open sysfs classes and their class devices.
These functions too operate with open and close, close must be called to
clean up the class structures. Given a class device name, functions are
provided to determine what class they belong to. Once a class device
name and the class it belongs to is known, a function to open the
class device is provided. This method can be used when details of
a single class device is required.
-------------------------------------------------------------------------------
Name: sysfs_open_class
Description: Function opens up one of the classes represented in sysfs in
the /sys/class directory. It returns a sysfs_class structure
that includes a list of class devices.
Arguments: const char *name Class name to open, like "net"..
Returns: struct sysfs_class * with success
NULL with error. Errno will be set with error, returning
- EINVAL for invalid arguments
Prototype: struct sysfs_class *sysfs_open_class(const char *name)
-------------------------------------------------------------------------------
-------------------------------------------------------------------------------
Name: sysfs_close_class
Description: Function closes up the sysfs_class structure including its
class devices.
Arguments: sysfs_class *cls Class structure to close
Prototype: void sysfs_close_class(struct sysfs_class *cls);
-------------------------------------------------------------------------------
-------------------------------------------------------------------------------
Name: sysfs_open_class_device_path
Description: Function opens up one of the class devices represented in
sysfs in sysfs/class/"class"/ directory. It returns a
sysfs_class_device structure.
Arguments: const char *path Path to class device
Returns: struct sysfs_class_device * with success
NULL with error. Errno will be set with error, returning
- EINVAL for invalid arguments
Prototype: struct sysfs_class_device *sysfs_open_class_device_path
(const char *path)
-------------------------------------------------------------------------------
-------------------------------------------------------------------------------
Name: sysfs_close_class_device
Description: Function closes up the sysfs_class_device structure.
Arguments: sysfs_class_device *dev Class device structure to close
Prototype: void sysfs_close_class_device(struct sysfs_class_device *dev)
-------------------------------------------------------------------------------
-------------------------------------------------------------------------------
Name: sysfs_get_class_device
Description: Function takes a sysfs_class structure(obtained on a successful
return from a sysfs_open_class() call) and looks for the given
device in this class. On success, it returns a
sysfs_class_device structure corresponding to the class device.
Arguments: struct sysfs_class *cls Class on which to search
char *name Class device "name" to look for
Returns: struct sysfs_class_device * with success
NULL with error. Errno will be set with error, returning
- EINVAL for invalid arguments
Prototype: struct sysfs_class_device *sysfs_get_class_device
(struct sysfs_class *cls, char *name)
-------------------------------------------------------------------------------
-------------------------------------------------------------------------------
Name: sysfs_get_class_devices
Description: Function returns a list of class devices for the given class.
Arguments: struct sysfs_class *cls Class whose class device list
is required
Returns: struct dlist * of sysfs_class_devices on success
NULL with error. Errno will be set with error, returning
- EINVAL for invalid arguments
Prototype: struct dlist *sysfs_get_class_devices(struct sysfs_class *cls)
-------------------------------------------------------------------------------
-------------------------------------------------------------------------------
Name: sysfs_open_class_device
Description: Given the name of the class on which to look for, this function
locates a given class device and returns a sysfs_class_device
structure corresponding to the requested class device.
NOTE:
1. The sysfs_class_device structure obtained upon successful
return from this function has to be closed by calling
sysfs_close_class_device().
2. Class this device belongs to must be known prior to calling
this function.
Arguments: const char *classname Class on which to search
char *name Class device "name" to open
Returns: struct sysfs_class_device * with success
NULL with error. Errno will be set with error, returning
- EINVAL for invalid arguments
Prototype: struct sysfs_class_device *sysfs_open_class_device
(const char *classname, char *name)
-------------------------------------------------------------------------------
-------------------------------------------------------------------------------
Name: sysfs_get_classdev_device
Description: Function returns the sysfs_device reference (if present) for the
given class device.
Arguments: struct sysfs_class_device *clsdev Class device whose
sysfs_device reference
is required
Returns: struct sysfs_device * on success
NULL with error. Errno will be set with error, returning
- EINVAL for invalid arguments
Prototype: struct sysfs_device *sysfs_get_classdev_device
(struct sysfs_class_device *clsdev)
-------------------------------------------------------------------------------
-------------------------------------------------------------------------------
Name: sysfs_get_classdev_parent
Description: Function returns the sysfs_class_device reference for the
parent (if present) of the given class device.
Arguments: struct sysfs_class_device *clsdev Class device whose
parent reference
is required
Returns: struct sysfs_class_device * on success
NULL with error. Errno will be set with error, returning
- EINVAL for invalid arguments
Prototype: struct sysfs_class_device *sysfs_get_classdev_parent
(struct sysfs_class_device *clsdev)
-------------------------------------------------------------------------------
-------------------------------------------------------------------------------
Name: sysfs_get_classdev_attributes
Description: Function takes a sysfs_class_device structure and returns a
list of attributes for the class device.
Arguments: struct sysfs_class_device *cdev Class device for which
attributes are required
Returns: struct dlist * of attributes with success
NULL with error. Errno will be set with error, returning
- EINVAL for invalid arguments
Prototype: struct dlist *sysfs_get_classdev_attributes
(struct sysfs_class_device *cdev)
-------------------------------------------------------------------------------
-------------------------------------------------------------------------------
Name: sysfs_get_classdev_attr
Description: Searches supplied class device's attributes by name and returns
the attribute.
Arguments: struct sysfs_class_device *clsdev Device to search
const char *name Attribute name to find
Returns: struct sysfs_attribute * with success
NULL with error. Errno will be set with error, returning
- EINVAL for invalid arguments
Prototype: struct sysfs_attribute *sysfs_get_classdev_attr
(struct sysfs_class_device *clsdev, const char *name)
-------------------------------------------------------------------------------
6.6 Device Functions
--------------------
Devices represent everything in sysfs under /sys/devices, which is a
hierarchical view of system devices. Besides the expected open and
close functions, libsysfs provides open and close functions for
root devices. These functions recursively open or close a device
and all of its children.
-------------------------------------------------------------------------------
Name: sysfs_open_device_path
Description: Opens up a device at a specific path. It opens the device's
directory, reads the directory, and returns a sysfs_device
structure.
Arguments: const char *path Path to device
Returns: struct sysfs_device * with success
NULL with error. Errno will be set with error, returning
- EINVAL for invalid arguments
Prototype: struct sysfs_device *sysfs_open_device_path(const char *path)
-------------------------------------------------------------------------------
-------------------------------------------------------------------------------
Name: sysfs_close_device
Description: Function closes up the sysfs_device structure.
Arguments: sysfs_device *dev Device structure to close
Prototype: void sysfs_close_device(struct sysfs_device *dev)
-------------------------------------------------------------------------------
-------------------------------------------------------------------------------
Name: sysfs_get_device_parent
Description: Function returns the sysfs_device reference for the parent
(if present) of the given sysfs_device.
Arguments: struct sysfs_device *dev sysfs_device whose parent
reference is required
Returns: struct sysfs_device * on success
NULL with error. Errno will be set with error, returning
- EINVAL for invalid arguments
Prototype: struct sysfs_device *sysfs_get_device_parent
(struct sysfs_device *dev)
-------------------------------------------------------------------------------
-------------------------------------------------------------------------------
Name: sysfs_get_device_attr
Description: Searches supplied device's attributes by name and returns
the attribute.
Arguments: struct sysfs_device *dev Device to search
const char *name Attribute name to find
Returns: struct sysfs_attribute * with success
NULL with error. Errno will be set with error, returning
- EINVAL for invalid arguments
Prototype: struct sysfs_attribute *sysfs_get_device_attr
(struct sysfs_device *dev, const char *name)
-------------------------------------------------------------------------------
-------------------------------------------------------------------------------
Name: sysfs_get_device_attributes
Description: Function takes a sysfs_device structure and returns a list
of attributes for the device.
Arguments: struct sysfs_device *device Device for which
attributes are required
Returns: struct dlist * of attributes with success
NULL with error. Errno will be set with error, returning
- EINVAL for invalid arguments
Prototype: struct dlist *sysfs_get_device_attributes
(struct sysfs_device *device)
-------------------------------------------------------------------------------
-------------------------------------------------------------------------------
Name: sysfs_open_device
Description: Given the name of the bus on which to look for, this function
locates a given device and returns a sysfs_device structure
corresponding to the requested device.
Arguments: const char *bus Bus on which to search
const char *bus_id Device to look for
Returns: struct sysfs_device * with success
NULL with error. Errno will be set with error, returning
- EINVAL for invalid arguments
Prototype: struct sysfs_device *sysfs_open_device
(const char *bus, const char *bus_id)
-------------------------------------------------------------------------------
-------------------------------------------------------------------------------
Name: sysfs_get_device_bus
Description: Given a sysfs_device, this function fills in the bus this
device is on in the sysfs_device->bus field.
Arguments: struct sysfs_device *dev Device whose bus name to find
Returns: 0 with success.
-1 with error. Errno will be set with error, returning
- EINVAL for invalid arguments
Prototype: int sysfs_get_device_bus(struct sysfs_device *dev)
-------------------------------------------------------------------------------
6.7 Driver Functions
--------------------
Drivers are represented in sysfs under the /sys/bus/xxx/drivers (xxx being
the bus type, such as "pci", "usb, and so on). Functions are provided to
open and close drivers.
-------------------------------------------------------------------------------
Name: sysfs_open_driver_path
Description: Opens driver at specific path.
Arguments: const char *path Path to driver
Returns: struct sysfs_driver * with success
NULL with error. Errno will be set with error, returning
- EINVAL for invalid arguments
Prototype: struct sysfs_driver *sysfs_open_driver_path(const char *path)
-------------------------------------------------------------------------------
-------------------------------------------------------------------------------
Name: sysfs_close_driver
Description: Closes and cleans up sysfs_driver structure.
Arguments: sysfs_driver *driver Driver structure to close
Prototype: void sysfs_close_driver(struct sysfs_driver *driver)
-------------------------------------------------------------------------------
-------------------------------------------------------------------------------
Name: sysfs_get_driver_devices
Description: Function returns a list of devices that use this driver.
Arguments: struct sysfs_driver *driver Driver whose devices list is
required
Returns: struct dlist * of sysfs_devices on success
NULL with error. Errno will be set with error, returning
- EINVAL for invalid arguments
Prototype: struct dlist *sysfs_get_driver_devices
(struct sysfs_driver *driver)
-------------------------------------------------------------------------------
-------------------------------------------------------------------------------
Name: sysfs_get_driver_attr
Description: Searches supplied driver's attributes by name and returns
the attribute.
Arguments: struct sysfs_driver *drv Driver to search
const char *name Attribute name to find
Returns: struct sysfs_attribute * with success
NULL with error. Errno will be set with error, returning
- EINVAL for invalid arguments
Prototype: struct sysfs_attribute *sysfs_get_driver_attr
(struct sysfs_driver *drv, const char *name)
-------------------------------------------------------------------------------
-------------------------------------------------------------------------------
Name: sysfs_get_driver_attributes
Description: Function takes a sysfs_driver structure and returns a list
of attributes for the driver.
Arguments: struct sysfs_driver *driver Driver for which attributes
are required
Returns: struct dlist * of attributes with success
NULL with error. Errno will be set with error, returning
- EINVAL for invalid arguments
Prototype: struct dlist *sysfs_get_driver_attributes
(struct sysfs_driver *driver)
-------------------------------------------------------------------------------
-------------------------------------------------------------------------------
Name: sysfs_open_driver
Description: Given the name of the bus on which to look for, this function
locates a given driver and returns a sysfs_driver structure
corresponding to the requested device.
NOTE:
1. The sysfs_driver structure obtained upon successful return
from this function has to be closed by calling
sysfs_close_driver_by_name().
Arguments: const char *bus_name Bus on which to search
const char *drv_name Driver name to look for
Returns: struct sysfs_driver * with success
NULL with error. Errno will be set with error, returning
- EINVAL for invalid arguments
Prototype: struct sysfs_driver *sysfs_open_driver(const char *bus_name,
const char *drv_name)
-------------------------------------------------------------------------------
-------------------------------------------------------------------------------
Name: sysfs_get_driver_module
Description: Function takes a sysfs_driver structure and returns the module
that the driver is using.
Arguments: struct sysfs_driver *drv Driver for which the module
details are required
Returns: struct sysfs_module * with success
NULL with error. Errno will be set with error, returning
- EINVAL for invalid arguments
Prototype: struct dlist *sysfs_get_driver_module
(struct sysfs_driver *drv)
-------------------------------------------------------------------------------
6.8 Module Functions
--------------------
Modules are represented in sysfs under the /sys/module. Functions are provided
to open and close modules.
-------------------------------------------------------------------------------
Name: sysfs_close_module
Description: Closes and cleans up the sysfs_module structure
Arguments: struct sysfs_module *module sysfs_module device to close
Prototype: void sysfs_close_module(struct sysfs_module *module);
-------------------------------------------------------------------------------
-------------------------------------------------------------------------------
Name: sysfs_open_module_path
Description: Opens and populates the sysfs_module struct
Arguments: const char *path path to the module to open
Returns: struct sysfs_module * with success and NULL if error
Prototype: struct sysfs_module *sysfs_open_module_path(const char *path);
-------------------------------------------------------------------------------
-------------------------------------------------------------------------------
Name: sysfs_open_module
Description: Opens specific module on a system
Arguments: const char *name Name of the module to open
Returns: struct sysfs_module * with success or NULL if error
Prototype: struct sysfs_module *sysfs_open_module(const char *name);
-------------------------------------------------------------------------------
-------------------------------------------------------------------------------
Name: sysfs_get_module_parms
Description: Get modules list of parameters
Arguments: sysfs_module whose parmameter list is required
Returns: dlist of parameters on SUCCESS and NULL on error
Prototype: struct dlist *sysfs_get_module_parms(struct sysfs_module *module);
-------------------------------------------------------------------------------
-------------------------------------------------------------------------------
Name: sysfs_get_module_sections
Description: Get the set of sections for this module
Arguments: sysfs_module whose list of sections is required
Returns: dlist of sections on SUCCESS and NULL on error
Prototype: struct dlist *sysfs_get_module_sections(struct sysfs_module *module);
-------------------------------------------------------------------------------
-------------------------------------------------------------------------------
Name: sysfs_get_module_attributes
Description: Get dlist of attributes for the requested sysfs_module
Arguments: sysfs_module for which attributes are needed
Returns: a dlist of attributes if exists, NULL otherwise
Prototype: struct dlist *sysfs_get_module_attributes(struct sysfs_module *module);
-------------------------------------------------------------------------------
-------------------------------------------------------------------------------
Name: sysfs_get_module_attr
Description: searches module's attributes by name
Arguments: module: to look through
name: name of the attribute
Returns: sysfs_attribute reference with success or NULL with error
Prototype: struct sysfs_attribute *sysfs_get_module_attr
(struct sysfs_module *module, const char *name);
-------------------------------------------------------------------------------
-------------------------------------------------------------------------------
Name: sysfs_get_module_parm
Description: searches module's parameters by name
Arguments: sysfs_module: to look through
parm: parameter name
Returns: sysfs_attribute on SUCCESS and NULL on error
Prototype: struct sysfs_attribute *sysfs_get_module_parm
(struct sysfs_module *module, const char *parm);
-------------------------------------------------------------------------------
-------------------------------------------------------------------------------
Name: sysfs_get_module_section
Description: searches module's sections by name
Arguments: sysfs_module: to look through
section: section name
Returns: sysfs_attribute * on SUCCESS and NULL on error
Prototype: struct sysfs_attribute *sysfs_get_module_section
(struct sysfs_module *module, const char *section);
-------------------------------------------------------------------------------
7 Dlists
--------
Libsysfs uses (yet another) list implementation thanks to Eric J Bohm.
7.1 Navigating a dlist
----------------------
Some library functions return a dlist of devices/drivers/attributes, etc.
To navigate the list returned the macro "dlist_for_each_data" is to be used.
------------------------------------------------------------------------------
Function/Macro name: dlist_for_each_data
Description: Walk the given list, returning a known data type/
structure in each iteration.
Arguments: struct dlist *list List pointer
data_iterator Data type/structure variable
contained in the list
datatype Data type/structure contained
in the list
Returns: On each iteration, "data_iterator" will contain a list
element of "datatype"
Usage example: The function sysfs_get_classdev_attributes() returns a
dlist of attributes. To navigate the list:
struct sysfs_attribute *attr = NULL;
struct dlist *attrlist = NULL;
.
.
.
attrlist = sysfs_get_classdev_attributes
(struct sysfs_class_device *cdev)
if (attrlist != NULL) {
dlist_for_each_data(attrlist, attr,
struct sysfs_attribute) {
.
.
.
}
}
-------------------------------------------------------------------------------
7.2 Custom sorting using dlist_sort_custom()
--------------------------------------------
As of release 1.2.0, libsysfs provides a new interface for custom sorting
of dlists. The API dlist_sort_custom() has been added for this purpose.
Applications that would like to define their own sorter function can now
make use of this API.
The sorter function must conform to the following prototype:
int compare(void *a, void*b)
dlist_sort_custom() expects that the compare function will:
return >0 for a before b
return <0 for b before a
return 0 for a == b
7.3 Custom filtering and sorting using dlist_filter_sort()
----------------------------------------------------------
As of release 2.0.0, libsysfs provides a new interface for custom filtering
and sorting of dlists. This API is similar to scandir() system call.
Applications can call this API with the following arguments: the list, pointer
to the filter function, pointer to the sorter function as in
dlist_sort_custom.
The filter function must conform to the following prototype:
int filter(void *a)
dlist_filter_sort expects that the filter function will:
return 0 for unwanted nodes
return 1 for required nodes
8. Usage
--------
Accessing devices through libsysfs is supposed to mirror accessing devices
in the filesystem it represents. Here's a typical order of operation:
- get sysfs mount point
- "open" sysfs category, ie. bus, class, or device
- work with category
- "close" sysfs category
9. Testsuite
------------
Version 2.0.0 of sysfsutils ships with a comprehensive testsuite. The testsuite
shipped as part of the "test" directory of the sysfsutils source package,
results in an executable "testlibsysfs" which will be installed in the
/usr/local/bin directory. Some of the salient features of the testsuite are:
a. Tests _every_ API exported by the library.
b. Tests are performed for all possible combinations of input parameters.
c. Detailed output is provided for the correct case.
d. Facility to redirect output of the tests to a normal file.
e. Number of iterations of tests can be specified.
The testsuite comes with its own configuration file "libsysfs.conf" in the
"test" directory. This file is used to generate a header file at the time
the tests are built.
To use the testsuite:
a. Modify the variables libsysfs.conf file to appropriate values for your
system. (The libsysfs.conf file contains comments describing what each
variable stands for and, in some cases, how to determine an appropriate
value for the system under test).
b. Build and install the testsuite.
c. Run the testsuite:
testlibsysfs <number of iterations> <logfile>
The default logfile is stdout.
NOTE: If the libsysfs.conf file is changed, make sure to run "make clean" in
the test directory and then a "make" for the changes to take effect.
10. Conclusion
--------------
Libsysfs is meant to provide a stable application programming interface to
sysfs. Applications can depend upon the library to access system devices
and functions exposed through sysfs.
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