VIDIOC_CREATE_BUFS — Create buffers for Memory Mapped or User Pointer or DMA Buffer I/O
|struct v4l2_create_buffers *argp|
File descriptor returned by
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.
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
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
to ensure that the requested format is supported by the driver.
Based on the format's
type field the requested buffer
size (for single-planar) or plane sizes (for multi-planar formats) will be
used for the allocated buffers. The driver may return an error if the size(s)
are not supported by the hardware (usually because they are too small).
The buffers created by this ioctl will have as minimum size the size
defined by the
format.pix.sizeimage field (or the
corresponding fields for other format types). Usually if the
format.pix.sizeimage field is less than the minimum
required for the given format, then an error will be returned since drivers will
typically not allow this. If it is larger, then the value will be used as-is.
In other words, the driver may reject the requested size, but if it is accepted
the driver will use it unchanged.
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
respectively. On return
count can be smaller than
the number requested.
Table A.1. struct v4l2_create_buffers
|__u32||The starting buffer index, returned by the driver.|
|__u32||The number of buffers requested or granted. If count == 0, then
|__u32||Applications set this field to
|struct v4l2_format||Filled in by the application, preserved by the driver.|
|__u32||A place holder for future extensions. Drivers and applications must set the array to zero.|
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 (
requested I/O method (
memory) or format
format field) is not valid.