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.. SPDX-License-Identifier: GPL-2.0
.. _GPIO_V2_GET_LINEINFO_WATCH_IOCTL:
********************************
GPIO_V2_GET_LINEINFO_WATCH_IOCTL
********************************
Name
====
GPIO_V2_GET_LINEINFO_WATCH_IOCTL - Enable watching a line for changes to its
request state and configuration information.
Synopsis
========
.. c:macro:: GPIO_V2_GET_LINEINFO_WATCH_IOCTL
``int ioctl(int chip_fd, GPIO_V2_GET_LINEINFO_WATCH_IOCTL, struct gpio_v2_line_info *info)``
Arguments
=========
``chip_fd``
The file descriptor of the GPIO character device returned by `open()`.
``info``
The :c:type:`line_info<gpio_v2_line_info>` struct to be populated, with
the ``offset`` set to indicate the line to watch
Description
===========
Enable watching a line for changes to its request state and configuration
information. Changes to line info include a line being requested, released
or reconfigured.
.. note::
Watching line info is not generally required, and would typically only be
used by a system monitoring component.
The line info does NOT include the line value.
The line must be requested using gpio-v2-get-line-ioctl.rst to access
its value, and the line request can monitor a line for events using
gpio-v2-line-event-read.rst.
By default all lines are unwatched when the GPIO chip is opened.
Multiple lines may be watched simultaneously by adding a watch for each.
Once a watch is set, any changes to line info will generate events which can be
read from the ``chip_fd`` as described in
gpio-v2-lineinfo-changed-read.rst.
Adding a watch to a line that is already watched is an error (**EBUSY**).
Watches are specific to the ``chip_fd`` and are independent of watches
on the same GPIO chip opened with a separate call to `open()`.
Return Value
============
On success 0 and ``info`` is populated with the current line info.
On error -1 and the ``errno`` variable is set appropriately.
Common error codes are described in error-codes.rst.
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