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.

RETURN VALUE

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.

SEE ALSO

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),