media-ioc-enum-links.rst

.. -*- coding: utf-8; mode: rst -*-

.. _media-ioc-enum-links:

**************************
ioctl MEDIA_IOC_ENUM_LINKS
**************************

NAME
====

MEDIA_IOC_ENUM_LINKS - Enumerate all pads and links for a given entity

SYNOPSIS
========

.. cpp:function:: int ioctl( int fd, int request, struct media_links_enum *argp )


ARGUMENTS
=========

``fd``
    File descriptor returned by :ref:`open() <media-func-open>`.

``request``
    MEDIA_IOC_ENUM_LINKS

``argp``


DESCRIPTION
===========

To enumerate pads and/or links for a given entity, applications set the
entity field of a struct :ref:`media_links_enum <media-links-enum>`
structure and initialize the struct
:ref:`media_pad_desc <media-pad-desc>` and struct
:ref:`media_link_desc <media-link-desc>` structure arrays pointed by
the ``pads`` and ``links`` fields. They then call the
MEDIA_IOC_ENUM_LINKS ioctl with a pointer to this structure.

If the ``pads`` field is not NULL, the driver fills the ``pads`` array
with information about the entity's pads. The array must have enough
room to store all the entity's pads. The number of pads can be retrieved
with the :ref:`MEDIA_IOC_ENUM_ENTITIES <media-ioc-enum-entities>`
ioctl.

If the ``links`` field is not NULL, the driver fills the ``links`` array
with information about the entity's outbound links. The array must have
enough room to store all the entity's outbound links. The number of
outbound links can be retrieved with the
:ref:`MEDIA_IOC_ENUM_ENTITIES <media-ioc-enum-entities>` ioctl.

Only forward links that originate at one of the entity's source pads are
returned during the enumeration process.


.. _media-links-enum:

.. flat-table:: struct media_links_enum
    :header-rows:  0
    :stub-columns: 0
    :widths:       1 1 2


    -  .. row 1

       -  __u32

       -  ``entity``

       -  Entity id, set by the application.

    -  .. row 2

       -  struct :ref:`media_pad_desc <media-pad-desc>`

       -  \*\ ``pads``

       -  Pointer to a pads array allocated by the application. Ignored if
	  NULL.

    -  .. row 3

       -  struct :ref:`media_link_desc <media-link-desc>`

       -  \*\ ``links``

       -  Pointer to a links array allocated by the application. Ignored if
	  NULL.



.. _media-pad-desc:

.. flat-table:: struct media_pad_desc
    :header-rows:  0
    :stub-columns: 0
    :widths:       1 1 2


    -  .. row 1

       -  __u32

       -  ``entity``

       -  ID of the entity this pad belongs to.

    -  .. row 2

       -  __u16

       -  ``index``

       -  0-based pad index.

    -  .. row 3

       -  __u32

       -  ``flags``

       -  Pad flags, see :ref:`media-pad-flag` for more details.



.. _media-link-desc:

.. flat-table:: struct media_link_desc
    :header-rows:  0
    :stub-columns: 0
    :widths:       1 1 2


    -  .. row 1

       -  struct :ref:`media_pad_desc <media-pad-desc>`

       -  ``source``

       -  Pad at the origin of this link.

    -  .. row 2

       -  struct :ref:`media_pad_desc <media-pad-desc>`

       -  ``sink``

       -  Pad at the target of this link.

    -  .. row 3

       -  __u32

       -  ``flags``

       -  Link flags, see :ref:`media-link-flag` for more details.


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.

EINVAL
    The struct :ref:`media_links_enum <media-links-enum>` ``id``
    references a non-existing entity.