xref: /kernel/linux/linux-6.6/Documentation/userspace-api/media/dvb/dmx-expbuf.rst

.. SPDX-License-Identifier: GFDL-1.1-no-invariants-or-later
.. c:namespace:: DTV.dmx

.. _DMX_EXPBUF:

****************
ioctl DMX_EXPBUF
****************

Name
====

DMX_EXPBUF - Export a buffer as a DMABUF file descriptor.

.. warning:: this API is still experimental

Synopsis
========

.. c:macro:: DMX_EXPBUF

``int ioctl(int fd, DMX_EXPBUF, struct dmx_exportbuffer *argp)``

Arguments
=========

``fd``
    File descriptor returned by :c:func:`open()`.

``argp``
    Pointer to struct :c:type:`dmx_exportbuffer`.

Description
===========

This ioctl is an extension to the memory mapping I/O method.
It can be used to export a buffer as a DMABUF file at any time after
buffers have been allocated with the :ref:`DMX_REQBUFS` ioctl.

To export a buffer, applications fill struct :c:type:`dmx_exportbuffer`.
Applications must set the ``index`` field. Valid index numbers
range from zero to the number of buffers allocated with :ref:`DMX_REQBUFS`
(struct :c:type:`dmx_requestbuffers` ``count``) minus one.
Additional flags may be posted in the ``flags`` field. Refer to a manual
for open() for details. Currently only O_CLOEXEC, O_RDONLY, O_WRONLY,
and O_RDWR are supported.
All other fields must be set to zero. In the
case of multi-planar API, every plane is exported separately using
multiple :ref:`DMX_EXPBUF` calls.

After calling :ref:`DMX_EXPBUF` the ``fd`` field will be set by a
driver, on success. This is a DMABUF file descriptor. The application may
pass it to other DMABUF-aware devices. It is recommended to close a DMABUF
file when it is no longer used to allow the associated memory to be reclaimed.

Examples
========

.. code-block:: c

    int buffer_export(int v4lfd, enum dmx_buf_type bt, int index, int *dmafd)
    {
	struct dmx_exportbuffer expbuf;

	memset(&expbuf, 0, sizeof(expbuf));
	expbuf.type = bt;
	expbuf.index = index;
	if (ioctl(v4lfd, DMX_EXPBUF, &expbuf) == -1) {
	    perror("DMX_EXPBUF");
	    return -1;
	}

	*dmafd = expbuf.fd;

	return 0;
    }

Return Value
============

On success 0 is returned, on error -1 and the ``errno`` variable is set
appropriately. The generic error codes are described at the
:ref:`Generic Error Codes <gen-errors>` chapter.

EINVAL
    A queue is not in MMAP mode or DMABUF exporting is not supported or
    ``flags`` or ``index`` fields are invalid.