ioctl MEDIA_IOC_ENUM_LINKS
&manvol;

# MEDIA_IOC_ENUM_LINKS

Enumerate all pads and links for a given entity

    	int ioctl
    	int fd
    	int request
    	struct media_links_enum *argp

## Arguments

`fd`

  File descriptor returned by `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 &media-links-enum; structure and initialize the &media-pad-desc; and &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 &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 &MEDIA-IOC-ENUM-ENTITIES; ioctl.

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

### struct media_links_enum

&cs-str;
__u32 | entity | Entity id, set by the application.
&media-pad-desc; | *pads | Pointer to a pads array allocated by the application. Ignored if NULL.
&media-link-desc; | *links | Pointer to a links array allocated by the application. Ignored if NULL.

### struct media_pad_desc

&cs-str;
__u32 | entity | ID of the entity this pad belongs to.
__u16 | index | 0-based pad index.
__u32 | flags | Pad flags, see for more details.

### Media pad flags

`MEDIA_PAD_FL_SINK` | Input pad, relative to the entity. Input pads sink data and are targets of links.
`MEDIA_PAD_FL_SOURCE` | Output pad, relative to the entity. Output pads source data and are origins of links.
`MEDIA_PAD_FL_MUST_CONNECT` | If this flag is set and the pad is linked to any other pad, then at least one of those links must be enabled for the entity to be able to stream. There could be temporary reasons (e.g. device configuration dependent) for the pad to need enabled links even when this flag isn't set; the absence of the flag doesn't imply there is none.

### struct media_link_desc

&cs-str;
&media-pad-desc; | source | Pad at the origin of this link.
&media-pad-desc; | sink | Pad at the target of this link.
__u32 | flags | Link flags, see for more details.

### Media link flags

`MEDIA_LNK_FL_ENABLED` | The link is enabled and can be used to transfer media data. When two or more links target a sink pad, only one of them can be enabled at a time.
`MEDIA_LNK_FL_IMMUTABLE` | The link enabled state can't be modified at runtime. An immutable link is always enabled.
`MEDIA_LNK_FL_DYNAMIC` | The link enabled state can be modified during streaming. This flag is set by drivers and is read-only for applications.

One and only one of `MEDIA_PAD_FL_SINK` and `MEDIA_PAD_FL_SOURCE` must be set for every pad.

&return-value;

EINVAL

  The &media-links-enum; id references a non-existing entity.