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0001 .. SPDX-License-Identifier: GFDL-1.1-no-invariants-or-later
0002 .. c:namespace:: DTV.dmx
0003 
0004 .. _DMX_EXPBUF:
0005 
0006 ****************
0007 ioctl DMX_EXPBUF
0008 ****************
0009 
0010 Name
0011 ====
0012 
0013 DMX_EXPBUF - Export a buffer as a DMABUF file descriptor.
0014 
0015 .. warning:: this API is still experimental
0016 
0017 Synopsis
0018 ========
0019 
0020 .. c:macro:: DMX_EXPBUF
0021 
0022 ``int ioctl(int fd, DMX_EXPBUF, struct dmx_exportbuffer *argp)``
0023 
0024 Arguments
0025 =========
0026 
0027 ``fd``
0028     File descriptor returned by :c:func:`open()`.
0029 
0030 ``argp``
0031     Pointer to struct :c:type:`dmx_exportbuffer`.
0032 
0033 Description
0034 ===========
0035 
0036 This ioctl is an extension to the memory mapping I/O method.
0037 It can be used to export a buffer as a DMABUF file at any time after
0038 buffers have been allocated with the :ref:`DMX_REQBUFS` ioctl.
0039 
0040 To export a buffer, applications fill struct :c:type:`dmx_exportbuffer`.
0041 Applications must set the ``index`` field. Valid index numbers
0042 range from zero to the number of buffers allocated with :ref:`DMX_REQBUFS`
0043 (struct :c:type:`dmx_requestbuffers` ``count``) minus one.
0044 Additional flags may be posted in the ``flags`` field. Refer to a manual
0045 for open() for details. Currently only O_CLOEXEC, O_RDONLY, O_WRONLY,
0046 and O_RDWR are supported.
0047 All other fields must be set to zero. In the
0048 case of multi-planar API, every plane is exported separately using
0049 multiple :ref:`DMX_EXPBUF` calls.
0050 
0051 After calling :ref:`DMX_EXPBUF` the ``fd`` field will be set by a
0052 driver, on success. This is a DMABUF file descriptor. The application may
0053 pass it to other DMABUF-aware devices. It is recommended to close a DMABUF
0054 file when it is no longer used to allow the associated memory to be reclaimed.
0055 
0056 Examples
0057 ========
0058 
0059 .. code-block:: c
0060 
0061     int buffer_export(int v4lfd, enum dmx_buf_type bt, int index, int *dmafd)
0062     {
0063         struct dmx_exportbuffer expbuf;
0064 
0065         memset(&expbuf, 0, sizeof(expbuf));
0066         expbuf.type = bt;
0067         expbuf.index = index;
0068         if (ioctl(v4lfd, DMX_EXPBUF, &expbuf) == -1) {
0069             perror("DMX_EXPBUF");
0070             return -1;
0071         }
0072 
0073         *dmafd = expbuf.fd;
0074 
0075         return 0;
0076     }
0077 
0078 Return Value
0079 ============
0080 
0081 On success 0 is returned, on error -1 and the ``errno`` variable is set
0082 appropriately. The generic error codes are described at the
0083 :ref:`Generic Error Codes <gen-errors>` chapter.
0084 
0085 EINVAL
0086     A queue is not in MMAP mode or DMABUF exporting is not supported or
0087     ``flags`` or ``index`` fields are invalid.