3.2.18. ioctl DMX_EXPBUF Name

DMX_EXPBUF - Export a buffer as a DMABUF file descriptor.


this API is still experimental Synopsis


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


File descriptor returned by open().


Pointer to struct 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 ioctl DMX_REQBUFS ioctl.

To export a buffer, applications fill struct dmx_exportbuffer. Applications must set the index field. Valid index numbers range from zero to the number of buffers allocated with ioctl DMX_REQBUFS (struct 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 ioctl DMX_EXPBUF calls.

After calling ioctl 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

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 Generic Error Codes chapter.


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