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DMX_EXPBUF - Export a buffer as a DMABUF file descriptor.
.. warning:: this API is still experimental
.. c:function:: int ioctl( int fd, DMX_EXPBUF, struct dmx_exportbuffer *argp )
File descriptor returned by :ref:`open() <dmx_fopen>`.
Pointer to struct :c:type:`dmx_exportbuffer`.
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.
.. 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) {
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.
A queue is not in MMAP mode or DMABUF exporting is not supported or
``flags`` or ``index`` fields are invalid.