VIDIOC_CREATE_BUFS — Create buffers for Memory Mapped or User Pointer or DMA Buffer I/O


int ioctl(int fd,
 int request,
 struct v4l2_create_buffers *argp);



File descriptor returned by open().






This is an experimental interface and may change in the future.

This ioctl is used to create buffers for memory mapped or user pointer or DMA buffer I/O. It can be used as an alternative or in addition to the VIDIOC_REQBUFS ioctl, when a tighter control over buffers is required. This ioctl can be called multiple times to create buffers of different sizes.

To allocate the device buffers applications must initialize the relevant fields of the v4l2_create_buffers structure. The count field must be set to the number of requested buffers, the memory field specifies the requested I/O method and the reserved array must be zeroed.

The format field specifies the image format that the buffers must be able to handle. The application has to fill in this struct v4l2_format. Usually this will be done using the VIDIOC_TRY_FMT or VIDIOC_G_FMT ioctl() to ensure that the requested format is supported by the driver. Unsupported formats will result in an error.

The buffers created by this ioctl will have as minimum size the size defined by the format.pix.sizeimage field. If the format.pix.sizeimage field is less than the minimum required for the given format, then sizeimage will be increased by the driver to that minimum to allocate the buffers. If it is larger, then the value will be used as-is. The same applies to the sizeimage field of the v4l2_plane_pix_format structure in the case of multiplanar formats.

When the ioctl is called with a pointer to this structure the driver will attempt to allocate up to the requested number of buffers and store the actual number allocated and the starting index in the count and the index fields respectively. On return count can be smaller than the number requested. The driver may also increase buffer sizes if required, however, it will not update sizeimage field values. The user has to use VIDIOC_QUERYBUF to retrieve that information.

Table A.1. struct v4l2_create_buffers

__u32indexThe starting buffer index, returned by the driver.
__u32countThe number of buffers requested or granted. If count == 0, then VIDIOC_CREATE_BUFS will set index to the current number of created buffers, and it will check the validity of memory and format.type. If those are invalid -1 is returned and errno is set to EINVAL error code, otherwise VIDIOC_CREATE_BUFS returns 0. It will never set errno to EBUSY error code in this particular case.
__u32memoryApplications set this field to V4L2_MEMORY_MMAP, V4L2_MEMORY_DMABUF or V4L2_MEMORY_USERPTR. See Table 3.5, “enum v4l2_memory”
struct v4l2_formatformatFilled in by the application, preserved by the driver.
__u32reserved[8]A place holder for future extensions.

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.


No memory to allocate buffers for memory mapped I/O.


The buffer type (format.type field), requested I/O method (memory) or format (format field) is not valid.