создание, получение и выпуск объекта устройства udev (create, acquire and release a udev device object)
Имя (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
Синопсис (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);
Описание (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.
Возвращаемое значение (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.
Смотри также (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),
