NAME         top

       udev_device_new_from_syspath, udev_device_new_from_devnum,
       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         top

       #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         top

       udev_device_new_from_syspath, udev_device_new_from_devnum,
       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

       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         top

       On success, udev_device_new_from_syspath(),
       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         top

       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),

COLOPHON         top

       This page is part of the systemd (systemd system and service manager)
       project.  Information about the project can be found at 
       ⟨⟩.  If you have a bug
       report for this manual page, see 
       ⟨⟩.  This
       page was obtained from the project's upstream Git repository 
       ⟨⟩ on 2017-03-13.  If you dis‐
       cover any rendering problems in this HTML version of the page, or you
       believe there is a better or more up-to-date source for the page, or
       you have corrections or improvements to the information in this
       COLOPHON (which is not part of the original manual page), send a mail

systemd 233                                  UDEV_DEVICE_NEW_FROM_SYSPATH(3)