122 lines
4.1 KiB
ReStructuredText
122 lines
4.1 KiB
ReStructuredText
.. -*- coding: utf-8; mode: rst -*-
|
|
|
|
.. _VIDIOC_CREATE_BUFS:
|
|
|
|
************************
|
|
ioctl VIDIOC_CREATE_BUFS
|
|
************************
|
|
|
|
Name
|
|
====
|
|
|
|
VIDIOC_CREATE_BUFS - Create buffers for Memory Mapped or User Pointer or DMA Buffer I/O
|
|
|
|
|
|
Synopsis
|
|
========
|
|
|
|
.. c:function:: int ioctl( int fd, VIDIOC_CREATE_BUFS, struct v4l2_create_buffers *argp )
|
|
:name: VIDIOC_CREATE_BUFS
|
|
|
|
|
|
Arguments
|
|
=========
|
|
|
|
``fd``
|
|
File descriptor returned by :ref:`open() <func-open>`.
|
|
|
|
``argp``
|
|
|
|
|
|
Description
|
|
===========
|
|
|
|
This ioctl is used to create buffers for :ref:`memory mapped <mmap>`
|
|
or :ref:`user pointer <userp>` or :ref:`DMA buffer <dmabuf>` I/O. It
|
|
can be used as an alternative or in addition to the
|
|
:ref:`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 struct :c:type:`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
|
|
:c:type:`v4l2_format`. Usually this will be done using the
|
|
:ref:`VIDIOC_TRY_FMT <VIDIOC_G_FMT>` or
|
|
:ref:`VIDIOC_G_FMT <VIDIOC_G_FMT>` ioctls 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 ``index`` fields respectively. On return ``count`` can be smaller
|
|
than the number requested.
|
|
|
|
|
|
.. c:type:: v4l2_create_buffers
|
|
|
|
.. tabularcolumns:: |p{4.4cm}|p{4.4cm}|p{8.7cm}|
|
|
|
|
.. flat-table:: struct v4l2_create_buffers
|
|
:header-rows: 0
|
|
:stub-columns: 0
|
|
:widths: 1 1 2
|
|
|
|
* - __u32
|
|
- ``index``
|
|
- The starting buffer index, returned by the driver.
|
|
* - __u32
|
|
- ``count``
|
|
- The number of buffers requested or granted. If count == 0, then
|
|
:ref:`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 :ref:`VIDIOC_CREATE_BUFS` returns
|
|
0. It will never set errno to ``EBUSY`` error code in this particular
|
|
case.
|
|
* - __u32
|
|
- ``memory``
|
|
- Applications set this field to ``V4L2_MEMORY_MMAP``,
|
|
``V4L2_MEMORY_DMABUF`` or ``V4L2_MEMORY_USERPTR``. See
|
|
:c:type:`v4l2_memory`
|
|
* - struct :c:type:`v4l2_format`
|
|
- ``format``
|
|
- Filled in by the application, preserved by the driver.
|
|
* - __u32
|
|
- ``reserved``\ [8]
|
|
- A place holder for future extensions. Drivers and applications
|
|
must set the array to zero.
|
|
|
|
|
|
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.
|
|
|
|
ENOMEM
|
|
No memory to allocate buffers for :ref:`memory mapped <mmap>` I/O.
|
|
|
|
EINVAL
|
|
The buffer type (``format.type`` field), requested I/O method
|
|
(``memory``) or format (``format`` field) is not valid.
|