udev_device_new_from_syspath(3) — Linux manual page


UDEV_DE...SYSPATH(3)  udev_device_new_from_syspath  UDEV_DE...SYSPATH(3)

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 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         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

HISTORY         top

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

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
       ⟨http://www.freedesktop.org/wiki/Software/systemd⟩.  If you have
       a bug report for this manual page, see
       This page was obtained from the project's upstream Git repository
       ⟨https://github.com/systemd/systemd.git⟩ on 2023-12-22.  (At that
       time, the date of the most recent commit that was found in the
       repository was 2023-12-22.)  If you discover 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 to

systemd 255                                         UDEV_DE...SYSPATH(3)

Pages that refer to this page: libudev(3)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)systemd.directives(7)systemd.index(7)