linux-sg2042/Documentation/ABI/testing/sysfs-devices-online

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What: /sys/devices/.../online
Date: April 2013
Contact: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Description:
The /sys/devices/.../online attribute is only present for
devices whose bus types provide .online() and .offline()
callbacks. The number read from it (0 or 1) reflects the value
of the device's 'offline' field. If that number is 1 and '0'
(or 'n', or 'N') is written to this file, the device bus type's
.offline() callback is executed for the device and (if
successful) its 'offline' field is updated accordingly. In
turn, if that number is 0 and '1' (or 'y', or 'Y') is written to
this file, the device bus type's .online() callback is executed
for the device and (if successful) its 'offline' field is
updated as appropriate.
After a successful execution of the bus type's .offline()
callback the device cannot be used for any purpose until either
it is removed (i.e. device_del() is called for it), or its bus
type's .online() is exeucted successfully.