Provided by: libudev-dev_229-4ubuntu4_amd64 bug


       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, udev_device_unref - Create, acquire and
       release a udev device object


       #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

       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
       │ExampleExplanation              │
       │b8:2          │ block device major:minor │
       │c128:1        │ char device major:minor  │
       │n3            │ network device ifindex   │
       │+sound:card29 │ kernel driver core       │
       │              │ subsystem:device name    │

       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_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),