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+.. 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.