NAME

       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

SYNOPSIS

       #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);

DESCRIPTION

       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
       ┌──────────────┬──────────────────────────┐
       │Example       │ Explanation              │
       ├──────────────┼──────────────────────────┤
       │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.

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.

HISTORY

       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.

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)