- It must provide a stable programming interfaces that applications can be built upon.

Transcription

1 System Utilities sysfs Library - libsysfs ========================================= Version: September 13, 2004 Contents Introduction 2. Requirements 3. Definitions 4. Overview 5. Data Structures 5.1 Directory and Attribute Data Structures Attribute Structure Link Structure Directory Structure 5.2 Bus Data Structure 5.3 Class Data Structures 5.4 Root Device Data Structure 5.5 Device Data Structure 5.6 Driver Data Structure 6. Functions 6.1 Calling Conventions in Libsysfs 6.2 Utility Functions 6.3 Filesystem Functions Attribute Functions Directory Link Functions Directory Functions 6.4 Bus Functions 6.5 Class Functions 6.6 Device Functions 6.7 Driver Functions 7. Dlists 7.1 Navigating a dlist 7.2 Custom sorting using dlist_sort_custom() 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.

2 - 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: - 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: 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

3 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: 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 #define SYSFS_PROC_MNTS #define SYSFS_BUS_NAME #define SYSFS_CLASS_NAME #define SYSFS_BLOCK_NAME #define SYSFS_DEVICES_NAME #define SYSFS_DRIVERS_NAME #define SYSFS_NAME_ATTRIBUTE "sysfs" "/proc/mounts" "bus" "class" "block" "devices" "drivers" "name" The library uses some definitions to mark maximum size of a sysfs name or path length: #define SYSFS_PATH_MAX 255 #define SYSFS_NAME_LEN 50 #define SYSFS_BUS_ID_SIZE 20 NOTE: a. As of release 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 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. 5.1 Directory and Attribute Data Structures The library implements structures to represent sysfs directories, links, and files.

4 5.1.1 Attribute Structure 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 */ unsigned short 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 a bitmask for defining if the attribute supports show(read) and/or store(write) Link Structure Symbolic links are used in sysfs to link bus or class views with particular devices. struct sysfs_link { char name[sysfs_name_len]; char path[sysfs_path_max]; char target[sysfs_path_max]; }; Link s name is stored in "name and it s target stored in "target". Absolute path to the link is stored in "path" Directory Structure The directory structure represents a sysfs directory: struct sysfs_directory { char name[sysfs_name_len]; char path[sysfs_path_max]; }; /* Private: for internal use only */ struct dlist *subdirs; struct dlist *links; struct dlist *attributes; The sysfs_directory structure includes the list of subdirectories, links and attributes. The "name" and absolute "path" are also stored in the structure. The sysfs_directory structure is intended for use internal to the library. Applications needing access to attributes and links from the directory will need to make appropriate calls (described below) to get the same. 5.2 Bus Data Structure

5 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]; }; /* Private: for internal use only */ struct dlist *drivers; struct dlist *devices; struct sysfs_directory *directory; 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. The bus directory is represented by the sysfs_directory structure and it contains references to all the subdirectories, links, and attributes. The sysfs_directory structure is for internal use only. The following functions may be used by applications to retrieve data from the sysfs_directory structure: struct dlist *sysfs_get_bus_attributes(struct sysfs_bus *bus) struct sysfs_attribute *sysfs_get_bus_attribute(struct sysfs_bus *bus, char *attrname) 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]; }; /* Private: for internal use only */ struct dlist *devices; struct sysfs_directory *directory; The sysfs_class represents device classes in sysfs like "net". It contains the class "name", "path" to the class, a list of class devices and the directory representation (for internal use only). struct sysfs_class_device { char name[sysfs_name_len]; char path[sysfs_path_max]; char classname[sysfs_name_len]; }; /* Private: for internal use only */ struct sysfs_class_device *parent; struct sysfs_device *sysdevice; /* NULL if virtual */ struct sysfs_driver *driver; /* NULL if not implemented */ struct sysfs_directory *directory;

6 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, its sysfs_device reference and that device s driver reference (if any). It also contains the name of the class device - like "eth0", its parent point (if present) and its sysfs directory information including links and attributes (for internal use only). The following function may be used by applications to retrieve data from the sysfs_directory structure: struct dlist *sysfs_get_classdev_attributes(struct sysfs_class_device *cdev); 5.4 Root Device Data Structure Device hierarchies in sysfs are represented under the /sys/devices directory structure. Sysfs devices typically spawn off from base devices which are represented by a sysfs_root_device. struct sysfs_root_device { char name[sysfs_name_len]; char path[sysfs_path_max]; }; /* Private: for internal use only */ struct dlist *devices; struct sysfs_directory *directory; The sysfs_root_device structure contains a list of "devices" that spawn off it. The name of the root device as represented under /sys/devices is read into "name" and the absolute path into "path" and its sysfs_directory information intended to be used internal to the library. 5.5 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]; 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; struct sysfs_directory *directory; 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 and a directory structure, which contains a list of the device s attributes (for internal use only). The following functions may be used to obtain information from sysfs_directory structure:

7 struct sysfs_attribute *sysfs_get_device_attribute(struct sysfs_device *dev, const char *name) struct dlist *sysfs_get_device_attributes(struct sysfs_device *device) 5.6 Driver Data Structure The sysfs_driver structure represents a device driver. struct sysfs_driver { char name[sysfs_name_len]; char path[sysfs_path_max]; }; /* Private: for internal use only */ struct dlist *devices; struct sysfs_directory *directory; The sysfs_driver structure contains a list of devices that use this driver, the name of the driver, its path, and its directory information, which includes the driver s attributes (for internal use only). The following function may be used to retrieve driver attribute information from the sysfs_directory structure: struct dlist *sysfs_get_driver_attributes(struct sysfs_driver *driver) 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. sysfs_get_mnt_path

8 Function finds the mount path for filesystem type "sysfs". Arguments: char *mnt_path Mount path buffer size_t len Size of mount path buffer 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); sysfs_get_name_from_path 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 0 with success. -1 on Error. Errno will be set with error, returning Prototype: int sysfs_get_name_from_path(const char *path, char *name, size_t *len) sysfs_get_link 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 0 with success -1 with error. Errno will be set with error, returning Prototype: int sysfs_get_link(const char *path, char *target, size_t len) sysfs_open_subsystem_list Function returns the list of entries for the given subsystem. If the argument is "bus", this function will return a list of buses ("pci", "scsi", etc) supported on the system. sysfs_close_list() has to be called to free the list obtained from this call. Arguments: char *name Subsystem to open, like "bus"..

9 dlist of entries for the subsystem on success NULL with error indicating the "name" subsystem is invalid. Prototype: struct dlist *sysfs_open_subsystem_list(char *name) sysfs_open_bus_devices_list Function returns the list of devices on the given bus. sysfs_close_list() has to be called to free the list obtained from this call. Arguments: char *name Bus name to open "pci"/"scsi"/"usb".. dlist of device names for the given bus on success NULL with error indicating the bus is not supported. Prototype: struct dlist *sysfs_open_bus_devices_list(char *name) sysfs_close_list 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) sysfs_path_is_dir Utility function to verify if a given path is to a directory. Arguments: const char *path Path to verify 0 on success, 1 on error Prototype: int sysfs_path_is_dir(const char *path) sysfs_path_is_file Utility function to verify if a given path is to a file. Arguments: const char *path Path to verify 0 on success, 1 on error Prototype: int sysfs_path_is_file(const char *path)

10 sysfs_path_is_link Utility function to verify if a given path is to a link. Arguments: const char *path Path to verify 0 on success, 1 on error Prototype: int sysfs_path_is_link(const char *path) 6.3 Filesystem Functions Libsysfs provides a set of functions to open, read, and close directories and attributes/files in sysfs. These functions mirror their filesystem function counterparts Attribute Functions Along with the usual open, read, and close functions, libsysfs provides a couple other functions for accessing attribute values. sysfs_open_attribute 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 struct sysfs_attribute * with success. Prototype: struct sysfs_attribute *sysfs_open_attribute(const char *path) sysfs_close_attribute Arguments: Cleans up and closes sysfs_attribute structure. struct sysfs_attribute *sysattr Attribute to close Prototype: void sysfs_close_attribute(struct sysfs_attribute *sysattr) sysfs_read_dir_attributes Arguments: Reads the given sysfs_directory to create a list of attributes. struct sysfs_directory *sysdir sysfs_directory whose attributes to read

11 struct dlist * of attributes on success NULL with error. Errno will be set on error, returning EINVAL for invalid arguments Prototype: struct dlist *sysfs_read_dir_attributes (struct sysfs_directory *sysdir) sysfs_refresh_dir_attributes Arguments: Given a list sysfs_directory, this function refreshes the list of attributes for the given directory. struct sysfs_directory *sysdir sysfs_ directory whose attributes list to refresh 0 with success. 1 with error. Errno will be set on error, returning EINVAL for invalid arguments Prototype: int sysfs_refresh_dir_attributes(struct sysfs_directory *sysdir) sysfs_get_dir_attributes Arguments: Returns a list of attributes for the given sysfs_directory. struct sysfs_directory *sysdir sysfs_directory whose attributes list to return struct dlist * of attributes with success NULL with error. Errno will be set on error, returning EINVAL for invalid arguments Prototype: struct dlist *sysfs_read_dir_attributes (struct sysfs_directory *sysdir) sysfs_read_attribute 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 0 with success. -1 with error. Errno will be set with error, returning Prototype: int sysfs_read_attribute(struct sysfs_attribute *sysattr) sysfs_write_attribute

12 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" 0 with success. -1 with error. Errno will be set with error, returning Prototype: int sysfs_write_attribute(struct sysfs_attribute *sysattr, const char *new_value, size_t len) sysfs_read_attribute_value Given a path to a specific attribute, function reads and returns its value to the supplied value buffer. Arguments: const char *attrpath Attribute path to read char *value Buffer to read in attribute s value size_t vsize Size of buffer 0 with success. -1 with error. Errno will be set with error, returning Prototype: int sysfs_read_attribute_value(const char *attrpath, char *value, size_t vsize) sysfs_get_value_from_attributes Function takes a single or linked list of sysfs attribute structures and returns the value of the specified attribute name. Arguments: struct dlist *attr Attribute list to search through const char *name Name of attribute whose value to retrieve char * attribute value with success. Prototype: char *sysfs_get_value_from_attributes (struct sysfs_attribute *attr, const char *name) sysfs_get_directory_attribute Function walks the list of attributes for the given sysfs

13 directory and returns the sysfs_attribute structure for the specified attribute name. Arguments: struct sysfs_directory *dir Directory in which to search char *attrname Attribute name to look for struct sysfs_attribute on success. Prototype: struct sysfs_attribute *sysfs_get_directory_attribute (struct sysfs_directory *dir, char *attrname) Link Functions Sysfs contains many symbolic links, like bus links to bus devices. Libsysfs treats links differently than directories due to processing differences. A link in the /sys/bus/"busname"/devices/ directory indicates a device in the /sys/devices directory. Through links we give the functionality to know what is and what isn t a link and the ability to query the links target. sysfs_open_link Opens a directory link. Arguments: const char *linkpath Path to link struct sysfs_link * with success. Prototype: struct sysfs_link *sysfs_open_link(const char *linkpath) sysfs_close_link Closes a directory link structure. Arguments: struct sysfs_link *ln Link to close Prototype: void sysfs_close_link(struct sysfs_link *ln) sysfs_read_dir_links Arguments: Reads the given sysfs_directory to create a list of links. struct sysfs_directory *sysdir sysfs_directory whose links to read struct dlist * of links with success NULL with error. Errno will be set on error, returning EINVAL for invalid arguments

14 Prototype: struct dlist *sysfs_read_dir_links (struct sysfs_directory *sysdir) sysfs_get_dir_links Arguments: Returns a list of links for the given sysfs_directory. struct sysfs_directory *sysdir sysfs_directory whose list of links to return struct dlist * of links with success NULL with error. Errno will be set on error, returning EINVAL for invalid arguments Prototype: struct dlist *sysfs_read_dir_links (struct sysfs_directory *sysdir) sysfs_get_directory_link Function walks the list of links for the given sysfs directory and returns the sysfs_link structure for the specified link name. Arguments: struct sysfs_directory *dir Directory in which to search char *linkname Link name to look for struct sysfs_link * with success. Prototype: struct sysfs_link *sysfs_get_directory_link (struct sysfs_directory *dir, char *linkname) sysfs_get_subdirectory_link Function walks the list of links for the given sysfs directory and its subdirectories returns the sysfs_link structure for the specified link name. Arguments: struct sysfs_directory *dir Directory in which to search char *linkname Link name to look for struct sysfs_link * with success. Prototype: struct sysfs_link *sysfs_get_subdirectory_link (struct sysfs_directory *dir, char *linkname) sysfs_refresh_dir_links Given a list sysfs_directory, this function refreshes the list

15 of links under the given directory. Arguments: struct sysfs_directory *sysdir sysfs_ directory whose links list to refresh 0 with success. 1 with error. Errno will be set on error, returning EINVAL for invalid arguments Prototype: int sysfs_refresh_dir_links(struct sysfs_directory *sysdir) Directory Functions Sysfs directories can represent every directory under sysfs. The structures keep track of subdirectories, links, and files. Like opendir, readdir, and closedir, libsysfs provides open, read, and close functions for working with sysfs directories. Open creates the sysfs_directory structure. Read reads in its contents - like subdirectories, links, and files. Close cleans it all up. sysfs_open_directory Opens a sysfs directory at a specific path Arguments: const char *path Directory path to open struct sysfs_directory * with success. Prototype: struct sysfs_directory *sysfs_open_directory(const char *path) sysfs_close_directory Arguments: Closes specific directory, its subdirectories, links, and files. struct sysfs_directory *sysdir Directory to close Prototype: void sysfs_close_directory(struct sysfs_directory *sysdir) sysfs_read_dir_subdirs Arguments: Reads the given sysfs_directory to create a list of subdirs. struct sysfs_directory *sysdir sysfs_directory whose subdirs have to be read struct dlist * of links with success NULL with error. Errno will be set on error, returning EINVAL for invalid arguments

16 Prototype: struct dlist *sysfs_read_dir_subdirs (struct sysfs_directory *sysdir) sysfs_read_directory Arguments: Read the supplied directory. Reading fills in the directory s contents like subdirectories, links, and attributes. struct sysfs_directory *sysdir Directory to read 0 with success. -1 with error. Errno will be set with error, returning Prototype: int sysfs_read_directory(struct sysfs_directory *sysdir) sysfs_read_all_subdirs Arguments: Reads all subdirs under a given supplied directory. struct sysfs_directory *sysdir Directory to read 0 with success. -1 with error. Errno will be set with error, returning Prototype: int sysfs_read_all_subdirs(struct sysfs_directory *sysdir) sysfs_get_subdirectory Function walks the directory tree for the given directory and returns a sysfs_directory structure for the specified directory name. Arguments: struct sysfs_directory *dir Directory in which to search char *subname Name of directory to look for struct sysfs_directory with success. Prototype: struct sysfs_directory *sysfs_get_subdirectory (struct sysfs_directory *dir, char *subname) sysfs_get_dir_subdirs Arguments: Returns a list of subdirs for the given sysfs_directory. struct sysfs_directory *sysdir sysfs_directory whose subdirectories list to return struct dlist * of directories with success

17 NULL with error. Errno will be set on error, returning EINVAL for invalid arguments Prototype: struct dlist *sysfs_read_dir_subdirs (struct sysfs_directory *sysdir) sysfs_refresh_dir_subdirs Arguments: Given a list sysfs_directory, this function refreshes the list of subdirectories under the given directory. struct sysfs_directory *sysdir sysfs_ directory whose subdirs list to refresh 0 with success. 1 with error. Errno will be set on error, returning EINVAL for invalid arguments Prototype: int sysfs_refresh_dir_subdirs(struct sysfs_directory *sysdir) 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. sysfs_open_bus 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"... struct sysfs_bus * with success Prototype: struct sysfs_bus *sysfs_open_bus(const char *name) sysfs_close_bus Function closes up the sysfs_bus structure including its devices, drivers, and directory. Arguments: sysfs_bus *bus Bus structure to close Prototype: void sysfs_close_bus(struct sysfs_bus *bus)

18 sysfs_get_bus_devices Function returns a list of devices that are registered with this bus. Arguments: struct sysfs_bus *bus Bus whose devices list to return struct dlist * of sysfs_devices on success NULL with error. Errno will be sent with error, returning Prototype: struct dlist *sysfs_get_bus_devices(struct sysfs_bus *bus) sysfs_get_bus_drivers Function returns a list of drivers that are registered with this bus. Arguments: struct sysfs_bus *bus Bus whose drivers list to return struct dlist * of sysfs_drivers on success NULL with error. Errno will be sent with error, returning Prototype: struct dlist *sysfs_get_bus_drivers(struct sysfs_bus *bus) sysfs_get_bus_device 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 struct sysfs_device * with success Prototype: struct sysfs_device *sysfs_get_bus_device (struct sysfs_bus *bus, char *id) sysfs_get_bus_driver 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

19 struct sysfs_driver * with success Prototype: struct sysfs_device *sysfs_get_bus_driver (struct sysfs_bus *bus, char *drvname) sysfs_get_bus_attributes Function takes a sysfs_bus structure and returns a list of attributes for the bus. Arguments: struct sysfs_bus *bus Bus for which attributes are required struct dlist * of attributes with success Prototype: struct dlist *sysfs_get_bus_attributes(struct sysfs_bus *bus) sysfs_get_bus_attribute Function takes a sysfs_bus structure and looks for the required attribute on the bus. On success, it returns a sysfs_attribute structure corresponding to the given attribute. Arguments: struct sysfs_bus *bus Bus structure on which to search char *attrname Attribute to look for struct sysfs_attribute * with success Prototype: struct sysfs_attribute *sysfs_get_bus_attribute (struct sysfs_bus *bus, char *attrname) sysfs_refresh_bus_attributes Function refreshes the list of attributes for a given sysfs_bus Arguments: struct sysfs_bus *bus Bus whose attributes list to refresh struct dlist * of attributes with success Prototype: struct dlist *sysfs_get_bus_attributes(struct sysfs_bus *bus) sysfs_find_driver_bus Given the name of a driver, this function finds the name of the

20 bus the driver is on Arguments: const char *driver Name of the driver to look for char *busname Buffer to return the bus name size_t bsize Size of the "busname" buffer 0 with success. -1 with error. Errno will be set with error, returning Prototype: int sysfs_find_driver_bus(const char *driver, char *busname, size_t bsize) 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. sysfs_open_class 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".. struct sysfs_class * with success Prototype: struct sysfs_class *sysfs_open_class(const char *name) sysfs_close_class 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); sysfs_open_class_device_path Function opens up one of the class devices represented in sysfs in sysfs/class/"class"/ directory. It returns a sysfs_class_device structure.

21 Arguments: const char *path Path to class device struct sysfs_class_device * with success Prototype: struct sysfs_class_device *sysfs_open_class_device_path (const char *path) sysfs_close_class_device Arguments: Function closes up the sysfs_class_device structure. sysfs_class_device *dev Class device structure to close Prototype: void sysfs_close_class_device(struct sysfs_class_device *dev) sysfs_get_class_device 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 struct sysfs_class_device * with success Prototype: struct sysfs_class_device *sysfs_get_class_device (struct sysfs_class *cls, char *name) sysfs_get_class_devices Function returns a list of class devices for the given class. Arguments: struct sysfs_class *cls Class whose class device list is required struct dlist * of sysfs_class_devices on success Prototype: struct dlist *sysfs_get_class_devices(struct sysfs_class *cls) sysfs_open_class_device 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.

22 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 struct sysfs_class_device * with success Prototype: struct sysfs_class_device *sysfs_open_class_device (const char *classname, char *name) sysfs_get_classdev_device 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 struct sysfs_device * on success Prototype: struct sysfs_device *sysfs_get_classdev_device (struct sysfs_class_device *clsdev) sysfs_get_classdev_driver Function returns the sysfs_driver reference (if present) for the given class device. Arguments: struct sysfs_class_device *clsdev Class device whose sysfs_driver reference is required struct sysfs_driver * on success Prototype: struct sysfs_driver *sysfs_get_classdev_driver (struct sysfs_class_device *clsdev) sysfs_get_classdev_parent Function returns the sysfs_class_device reference for the parent (if present) of the given class device.

23 Arguments: struct sysfs_class_device *clsdev Class device whose parent reference is required struct sysfs_class_device * on success Prototype: struct sysfs_class_device *sysfs_get_classdev_parent (struct sysfs_class_device *clsdev) sysfs_get_classdev_attributes 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 struct dlist * of attributes with success Prototype: struct dlist *sysfs_get_classdev_attributes (struct sysfs_class_device *cdev) sysfs_get_classdev_attr 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 struct sysfs_attribute * with success Prototype: struct sysfs_attribute *sysfs_get_classdev_attr (struct sysfs_class_device *clsdev, const char *name) sysfs_refresh_classdev_attributes Arguments: Function refreshes the list of attributes for a given sysfs_class_device. struct sysfs_class_device *cdev Class device whose attributes list to refresh struct dlist * of attributes with success

24 Prototype: struct dlist *sysfs_get_classdev_attributes (struct sysfs_class_device *cdev) sysfs_open_classdev_attr NOTE: Function takes as arguments, a the name of the class, the class device name and the name of the required attribute. 1. The struct sysfs_attribute * obtained upon successful return from this function has to be closed by making a call to sysfs_close_attribute() Arguments: char *classname Class name on which to search char *dev Name of the class device char *attrib Attribute to open struct sysfs_attribute * with success. Prototype: struct sysfs_attribute *sysfs_write_classdev_attr (const char *classname, const char *dev, const char *attrib) 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. sysfs_open_device_path 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 struct sysfs_device * with success Prototype: struct sysfs_device *sysfs_open_device_path(const char *path) sysfs_close_device Function closes up the sysfs_device structure. Arguments: sysfs_device *dev Device structure to close

25 Prototype: void sysfs_close_device(struct sysfs_device *dev) sysfs_open_root_device Function opens up one of the root devices represented in sysfs in the /sys/devices directory. It returns a sysfs_root_device structure that includes a list of devices in the tree. Arguments: const char *name Name of the root device to open struct sysfs_root_device * with success Prototype: struct sysfs_device *sysfs_open_root_device(const char *name) sysfs_close_root_device Function closes up the sysfs_root_device structure including the devices in the root device tree. Arguments: sysfs_device *root Root device structure to close Prototype: void sysfs_close_root_device(struct sysfs_root_device *root) sysfs_open_device_tree Function opens up the device tree at the specified path. Arguments: const char *path Path at which to open the device tree struct sysfs_device * with success NULL with error, Errno will be set with error, returning Prototype: struct sysfs_device *sysfs_open_device_tree(const char *path) sysfs_close_device_tree Function closes the device tree originating at the given sysfs_device. Arguments: struct sysfs_device *devroot Device from which the device tree has to be closed Prototype: void sysfs_close_device_tree(struct sysfs_device *devroot) sysfs_get_device_parent

26 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 struct sysfs_device * on success Prototype: struct sysfs_device *sysfs_get_device_parent (struct sysfs_device *dev) sysfs_get_root_devices Arguments: Function returns a list of devices under the given root device. struct sysfs_root_device *root sysfs_root_device whose devices list is required struct dlist * of sysfs_devices on success Prototype: struct dlist *sysfs_get_root_devices (struct sysfs_root_device *root) sysfs_get_device_attr 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 struct sysfs_attribute * with success Prototype: struct sysfs_attribute *sysfs_get_device_attr (struct sysfs_device *dev, const char *name) sysfs_get_device_attributes 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 struct dlist * of attributes with success

27 Prototype: struct dlist *sysfs_get_device_attributes (struct sysfs_device *device) sysfs_refresh_device_attributes Function refreshes the list of attributes for a given sysfs_device. Arguments: struct sysfs_device *device Device whose attributes list to refresh struct dlist * of attributes with success Prototype: struct dlist *sysfs_refresh_device_attributes (struct sysfs_device *device) sysfs_open_device 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 struct sysfs_device * with success Prototype: struct sysfs_device *sysfs_open_device (const char *bus, const char *bus_id) sysfs_get_device_bus 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 0 with success. -1 with error. Errno will be set with error, returning Prototype: int sysfs_get_device_bus(struct sysfs_device *dev) sysfs_open_device_attr Function takes as arguments, the bus on which to search for a device, and an attribute of the device to open.

28 NOTE: 1. The struct sysfs_attribute * obtained upon successful return from this function has to be closed by making a call to sysfs_close_attribute() Arguments: char *bus Bus on which to search char *bus_id Device to look for char *attrib Name of the attribute to open struct sysfs_attribute * with success. Prototype: struct sysfs_attribute *sysfs_open_device_attr (const char *bus, const char *bus_id, const char *attrib) 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. sysfs_open_driver_path Opens driver at specific path. Arguments: const char *path Path to driver struct sysfs_driver * with success Prototype: struct sysfs_driver *sysfs_open_driver_path(const char *path) sysfs_close_driver Closes and cleans up sysfs_driver structure. Arguments: sysfs_driver *driver Driver structure to close Prototype: void sysfs_close_driver(struct sysfs_driver *driver) sysfs_get_driver_devices Function returns a list of devices that use this driver. Arguments: struct sysfs_driver *driver Driver whose devices list is required struct dlist * of sysfs_devices on success

29 Prototype: struct dlist *sysfs_get_driver_devices (struct sysfs_driver *driver) sysfs_refresh_driver_devices Function refreshes the list of devices that use this driver. Arguments: struct sysfs_driver *driver Driver whose devices list is required to be refreshed struct dlist * of sysfs_devices on success Prototype: struct dlist *sysfs_refresh_driver_devices (struct sysfs_driver *driver) sysfs_get_driver_device Function returns a sysfs_device reference for the device with "name" that uses this driver Arguments: struct sysfs_driver *driver Driver on which to search const char *name Name of the device to look for struct sysfs_device * corresponding to "name" on success Prototype: struct dlist *sysfs_get_driver_device (struct sysfs_driver *driver, const char *name) sysfs_get_driver_attr 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 struct sysfs_attribute * with success Prototype: struct sysfs_attribute *sysfs_get_driver_attr (struct sysfs_driver *drv, const char *name) sysfs_get_driver_attributes Function takes a sysfs_driver structure and returns a list of attributes for the driver.

30 Arguments: struct sysfs_driver *driver Driver for which attributes are required struct dlist * of attributes with success Prototype: struct dlist *sysfs_get_driver_attributes (struct sysfs_driver *driver) sysfs_refresh_driver_attributes Function refreshes the list of attributes for a given sysfs_driver. Arguments: struct sysfs_driver *driver Driver whose attributes list to refresh struct dlist * of attributes with success Prototype: struct dlist *sysfs_refresh_driver_attributes (struct sysfs_driver *driver) sysfs_open_driver NOTE: 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. 1. The sysfs_driver structure obtained upon successful return from this function has to be closed by calling sysfs_close_driver_by_name(). 2. Bus on which to look for this driver should be known prior to calling this function. Use sysfs_find_driver_bus() to determine this. Arguments: const char *bus_name Bus on which to search const char *drv_name Driver name to look for struct sysfs_driver * with success Prototype: struct sysfs_driver *sysfs_open_driver(const char *bus_name, const char *drv_name) sysfs_get_driver_links Function returns a list of links for a given driver

31 Arguments: struct sysfs_driver *driver Driver to get links from struct dlist * of links on success NULL with error Prototype: struct dlist *sysfs_get_driver_links (struct sysfs_driver *driver) sysfs_open_driver_attr NOTE: Function takes as arguments, the bus the driver is registered on, the driver name and the name of the attribute to open. 1. The struct sysfs_attribute * obtained upon successful return from this function has to be closed by making a call to sysfs_close_attribute() Arguments: char *bus Bus on which driver is present char *drv Driver to look for char *attrib Name of the attribute to open struct sysfs_attribute * with success. Prototype: struct sysfs_attribute *sysfs_open_driver_attr (const char *bus, const char *drv, const char *attrib) 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 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 On each iteration, "data_iterator" will contain a list element of "datatype"

32 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 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 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.

33 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. This is a demo version of txt2pdf v.10.1 Developed by SANFACE Software Available at