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+.. SPDX-License-Identifier: GPL-2.0
+
+.. _GPIO_V2_LINE_EVENT_READ:
+
+***********************
+GPIO_V2_LINE_EVENT_READ
+***********************
+
+Name
+====
+
+GPIO_V2_LINE_EVENT_READ - Read edge detection events for lines from a request.
+
+Synopsis
+========
+
+``int read(int req_fd, void *buf, size_t count)``
+
+Arguments
+=========
+
+``req_fd``
+    The file descriptor of the GPIO character device, as returned in the
+    :c:type:`request.fd<gpio_v2_line_request>` by gpio-v2-get-line-ioctl.rst.
+
+``buf``
+    The buffer to contain the :c:type:`events<gpio_v2_line_event>`.
+
+``count``
+    The number of bytes available in ``buf``, which must be at
+    least the size of a :c:type:`gpio_v2_line_event`.
+
+Description
+===========
+
+Read edge detection events for lines from a request.
+
+Edge detection must be enabled for the input line using either
+``GPIO_V2_LINE_FLAG_EDGE_RISING`` or ``GPIO_V2_LINE_FLAG_EDGE_FALLING``, or
+both. Edge events are then generated whenever edge interrupts are detected on
+the input line.
+
+The kernel captures and timestamps edge events as close as possible to their
+occurrence and stores them in a buffer from where they can be read by
+userspace at its convenience using `read()`.
+
+Events read from the buffer are always in the same order that they were
+detected by the kernel, including when multiple lines are being monitored by
+the one request.
+
+The size of the kernel event buffer is fixed at the time of line request
+creation, and can be influenced by the
+:c:type:`request.event_buffer_size<gpio_v2_line_request>`.
+The default size is 16 times the number of lines requested.
+
+The buffer may overflow if bursts of events occur quicker than they are read
+by userspace. If an overflow occurs then the oldest buffered event is
+discarded. Overflow can be detected from userspace by monitoring the event
+sequence numbers.
+
+To minimize the number of calls required to copy events from the kernel to
+userspace, `read()` supports copying multiple events. The number of events
+copied is the lower of the number available in the kernel buffer and the
+number that will fit in the userspace buffer (``buf``).
+
+Changing the edge detection flags using gpio-v2-line-set-config-ioctl.rst
+does not remove or modify the events already contained in the kernel event
+buffer.
+
+The `read()` will block if no event is available and the ``req_fd`` has not
+been set **O_NONBLOCK**.
+
+The presence of an event can be tested for by checking that the ``req_fd`` is
+readable using `poll()` or an equivalent.
+
+Return Value
+============
+
+On success the number of bytes read, which will be a multiple of the size of a
+:c:type:`gpio_v2_line_event` event.
+
+On error -1 and the ``errno`` variable is set appropriately.
+Common error codes are described in error-codes.rst.