USB_SET_DEVICE_STATE(9) USB Core APIs USB_SET_DEVICE_STATE(9)NAME
usb_set_device_state - change a device's current state (usbcore, hcds)
SYNOPSIS
void usb_set_device_state(struct usb_device * udev, enum usb_device_state new_state);
ARGUMENTS
udev
pointer to device whose state should be changed
new_state
new state value to be stored
DESCRIPTION
udev->state is _not_ fully protected by the device lock. Although most transitions are made only while holding the lock, the state can can
change to USB_STATE_NOTATTACHED at almost any time. This is so that devices can be marked as disconnected as soon as possible, without
having to wait for any semaphores to be released. As a result, all changes to any device's state must be protected by the device_state_lock
spinlock.
Once a device has been added to the device tree, all changes to its state should be made using this routine. The state should _not_ be set
directly.
If udev->state is already USB_STATE_NOTATTACHED then no change is made. Otherwise udev->state is set to new_state, and if new_state is
USB_STATE_NOTATTACHED then all of udev's descendants' states are also set to USB_STATE_NOTATTACHED.
COPYRIGHT Kernel Hackers Manual 3.10 June 2014 USB_SET_DEVICE_STATE(9)
Check Out this Related Man Page
SYSTEMD.DEVICE(5) systemd.device SYSTEMD.DEVICE(5)NAME
systemd.device - Device unit configuration
SYNOPSIS
device.device
DESCRIPTION
A unit configuration file whose name ends in ".device" encodes information about a device unit as exposed in the sysfs/udev(7) device tree.
This unit type has no specific options. See systemd.unit(5) for the common options of all unit configuration files. The common
configuration items are configured in the generic "[Unit]" and "[Install]" sections. A separate "[Device]" section does not exist, since no
device-specific options may be configured.
systemd will dynamically create device units for all kernel devices that are marked with the "systemd" udev tag (by default all block and
network devices, and a few others). This may be used to define dependencies between devices and other units. To tag a udev device, use
"TAG+="systemd"" in the udev rules file, see udev(7) for details.
Device units are named after the /sys and /dev paths they control. Example: the device /dev/sda5 is exposed in systemd as dev-sda5.device.
For details about the escaping logic used to convert a file system path to a unit name see systemd.unit(5).
Device units will be reloaded by systemd whenever the corresponding device generates a "changed" event. Other units can use
ReloadPropagatedFrom= to react to that event
IMPLICIT DEPENDENCIES
Many unit types automatically acquire dependencies on device units of devices they require. For example, .socket unit acquire dependencies
on the device units of the network interface specified in BindToDevice=. Similar, swap and mount units acquire dependencies on the units
encapsulating their backing block devices.
DEFAULT DEPENDENCIES
There are no default dependencies for device units.
THE UDEV DATABASE
Unit settings of device units may either be configured via unit files, or directly from the udev database. The following udev device
properties are understood by the service manager:
SYSTEMD_WANTS=, SYSTEMD_USER_WANTS=
Adds dependencies of type Wants= from the device unit to the specified units. SYSTEMD_WANTS= is read by the system service manager,
SYSTEMD_USER_WANTS= by user service manager instances. These properties may be used to activate arbitrary units when a specific device
becomes available.
Note that this and the other udev device properties are not taken into account unless the device is tagged with the "systemd" tag in
the udev database, because otherwise the device is not exposed as a systemd unit (see above).
Note that systemd will only act on Wants= dependencies when a device first becomes active. It will not act on them if they are added to
devices that are already active. Use SYSTEMD_READY= (see below) to configure when a udev device shall be considered active, and thus
when to trigger the dependencies.
The specified property value should be a space-separated list of valid unit names. If a unit template name is specified (that is, a
unit name containing an "@" character indicating a unit name to use for multiple instantiation, but with an empty instance name
following the "@"), it will be automatically instantiated by the device's "sysfs" path (that is: the path is escaped and inserted as
instance name into the template unit name). This is useful in order to instantiate a specific template unit once for each device that
appears and matches specific properties.
SYSTEMD_ALIAS=
Adds an additional alias name to the device unit. This must be an absolute path that is automatically transformed into a unit name.
(See above.)
SYSTEMD_READY=
If set to 0, systemd will consider this device unplugged even if it shows up in the udev tree. If this property is unset or set to 1,
the device will be considered plugged if it is visible in the udev tree.
This option is useful for devices that initially show up in an uninitialized state in the tree, and for which a "changed" event is
generated the moment they are fully set up. Note that SYSTEMD_WANTS= (see above) is not acted on as long as SYSTEMD_READY=0 is set for
a device.
ID_MODEL_FROM_DATABASE=, ID_MODEL=
If set, this property is used as description string for the device unit.
SEE ALSO systemd(1), systemctl(1), systemd.unit(5), udev(7), systemd.directives(7)systemd 237 SYSTEMD.DEVICE(5)