Documentation/userspace-api/gpio/gpio-v2-get-lineinfo-watch-ioctl.rst

.. 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.