MEDIA_IOC_ENUM_LINKS — Enumerate all pads and links for a given entity
int ioctl( | int fd, |
| int request, | |
struct media_links_enum *argp); |
To enumerate pads and/or links for a given entity, applications set
the entity field of a struct media_links_enum structure and initialize the
struct media_pad_desc and struct 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.
Table L.5. struct media_links_enum
| __u32 | entity | Entity id, set by the application. |
| struct media_pad_desc | *pads | Pointer to a pads array allocated by the application. Ignored if NULL. |
| struct media_link_desc | *links | Pointer to a links array allocated by the application. Ignored if NULL. |
Table L.6. struct media_pad_desc
| __u32 | entity | ID of the entity this pad belongs to. |
| __u16 | index | 0-based pad index. |
| __u32 | flags | Pad flags, see Table L.7, “Media pad flags” for more details. |
Table L.7. 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. |
Table L.8. struct media_link_desc
| struct media_pad_desc | source | Pad at the origin of this link. |
| struct media_pad_desc | sink | Pad at the target of this link. |
| __u32 | flags | Link flags, see Table L.9, “Media link flags” for more details. |
Table L.9. 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.
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.
The struct media_links_enum id references
a non-existing entity.