udev_device_new_from_syspath - Man Page

#include <libudev​.h>

struct udev_device *udev_device_new_from_syspath(struct udev *udev, const char *syspath);

struct udev_device *udev_device_new_from_devnum(struct udev *udev, char type, dev_t devnum);

struct udev_device *udev_device_new_from_subsystem_sysname(struct udev *udev, const char *subsystem, const char *sysname);

struct udev_device *udev_device_new_from_device_id(struct udev *udev, const char *id);

struct udev_device *udev_device_new_from_environment(struct udev *udev);

struct udev_device *udev_device_ref(struct udev_device *udev_device);

struct udev_device *udev_device_unref(struct udev_device *udev_device);

udev_device_new_from_syspath(), udev_device_new_from_devnum(), udev_device_new_from_subsystem_sysname(), udev_device_new_from_device_id(), and udev_device_new_from_environment() allocate a new udev device object and returns a pointer to it​. This object is opaque and must not be accessed by the caller via different means than functions provided by libudev​. Initially, the reference count of the device is 1​. You can acquire further references, and drop gained references via udev_device_ref() and udev_device_unref()​. Once the reference count hits 0, the device object is destroyed and freed​.

udev_device_new_from_syspath(), udev_device_new_from_devnum(), udev_device_new_from_subsystem_sysname(), and udev_device_new_from_device_id() create the device object based on information found in /sys/, annotated with properties from the udev-internal device database​. A syspath is any subdirectory of /sys/, with the restriction that a subdirectory of /sys/devices (or a symlink to one) represents a real device and as such must contain a uevent file​. udev_device_new_from_devnum() takes a device type, which can be b for block devices or c for character devices, as well as a devnum (see makedev(3))​. udev_device_new_from_subsystem_sysname() looks up devices based on the provided subsystem and sysname (see udev_device_get_subsystem(3) and udev_device_get_sysname(3)) and udev_device_new_from_device_id() looks up devices based on the provided device ID, which is a special string in one of the following four forms:

Table ​1. ​Device ID strings

udev_device_new_from_environment() creates a device from the current environment (see environ(7))​. Each key-value pair is interpreted in the same way as if it was received in an uevent (see udev_monitor_receive_device(3))​. The keys DEVPATH, SUBSYSTEM, ACTION, and SEQNUM are mandatory​.

On success, udev_device_new_from_syspath(), udev_device_new_from_devnum(), udev_device_new_from_subsystem_sysname(), udev_device_new_from_device_id() and udev_device_new_from_environment() return a pointer to the allocated udev device​. On failure, NULL is returned, and errno is set appropriately​. udev_device_ref() returns the argument that it was passed, unmodified​. udev_device_unref() always returns NULL​.

udev_device_new_from_syspath(), udev_device_new_from_devnum(), udev_device_new_from_subsystem_sysname(), udev_device_new_from_device_id(), udev_device_new_from_environment(), udev_device_ref(), and udev_device_unref() were added in version 221​.

udev_new(3), udev_device_get_syspath(3), udev_device_has_tag(3), udev_enumerate_new(3), udev_monitor_new_from_netlink(3), udev_list_entry(3), systemd(1)

libudev(3), systemd.directives(7), systemd.index(7), udev_device_get_syspath(3), udev_device_has_tag(3), udev_enumerate_add_match_subsystem(3), udev_enumerate_new(3), udev_enumerate_scan_devices(3), udev_list_entry(3), udev_monitor_filter_update(3), udev_monitor_new_from_netlink(3), udev_monitor_receive_device(3).

The man pages udev_device_new_from_device_id(3), udev_device_new_from_devnum(3), udev_device_new_from_environment(3), udev_device_new_from_subsystem_sysname(3), udev_device_ref(3) and udev_device_unref(3) are aliases of udev_device_new_from_syspath(3).