6.5. ioctl MEDIA_IOC_G_TOPOLOGY

6.5.1. Name

MEDIA_IOC_G_TOPOLOGY - Enumerate the graph topology and graph element properties

6.5.2. Synopsis

int ioctl(int fd, MEDIA_IOC_G_TOPOLOGY, struct media_v2_topology *argp)

6.5.3. Arguments

fd
File descriptor returned by open().
argp
Pointer to struct media_v2_topology.

6.5.4. Description

The typical usage of this ioctl is to call it twice. On the first call, the structure defined at struct media_v2_topology should be zeroed. At return, if no errors happen, this ioctl will return the topology_version and the total number of entities, interfaces, pads and links.

Before the second call, the userspace should allocate arrays to store the graph elements that are desired, putting the pointers to them at the ptr_entities, ptr_interfaces, ptr_links and/or ptr_pads, keeping the other values untouched.

If the topology_version remains the same, the ioctl should fill the desired arrays with the media graph elements.

media_v2_topology
struct media_v2_topology
__u64 topology_version Version of the media graph topology. When the graph is created, this field starts with zero. Every time a graph element is added or removed, this field is incremented.
__u32 num_entities Number of entities in the graph
__u32 reserved1 Applications and drivers shall set this to 0.
__u64 ptr_entities A pointer to a memory area where the entities array will be stored, converted to a 64-bits integer. It can be zero. if zero, the ioctl won’t store the entities. It will just update num_entities
__u32 num_interfaces Number of interfaces in the graph
__u32 reserved2 Applications and drivers shall set this to 0.
__u64 ptr_interfaces A pointer to a memory area where the interfaces array will be stored, converted to a 64-bits integer. It can be zero. if zero, the ioctl won’t store the interfaces. It will just update num_interfaces
__u32 num_pads Total number of pads in the graph
__u32 reserved3 Applications and drivers shall set this to 0.
__u64 ptr_pads A pointer to a memory area where the pads array will be stored, converted to a 64-bits integer. It can be zero. if zero, the ioctl won’t store the pads. It will just update num_pads
__u32 num_links Total number of data and interface links in the graph
__u32 reserved4 Applications and drivers shall set this to 0.
__u64 ptr_links A pointer to a memory area where the links array will be stored, converted to a 64-bits integer. It can be zero. if zero, the ioctl won’t store the links. It will just update num_links
media_v2_entity
struct media_v2_entity
__u32 id Unique ID for the entity. Do not expect that the ID will always be the same for each instance of the device. In other words, do not hardcode entity IDs in an application.
char name[64] Entity name as an UTF-8 NULL-terminated string. This name must be unique within the media topology.
__u32 function Entity main function, see Media entity functions for details.
__u32 flags Entity flags, see Media entity flags for details. Only valid if MEDIA_V2_ENTITY_HAS_FLAGS(media_version) returns true. The media_version is defined in struct media_device_info and can be retrieved using ioctl MEDIA_IOC_DEVICE_INFO.
__u32 reserved[5] Reserved for future extensions. Drivers and applications must set this array to zero.
media_v2_interface
struct media_v2_interface
__u32 id Unique ID for the interface. Do not expect that the ID will always be the same for each instance of the device. In other words, do not hardcode interface IDs in an application.
__u32 intf_type Interface type, see Media interface types for details.
__u32 flags Interface flags. Currently unused.
__u32 reserved[9] Reserved for future extensions. Drivers and applications must set this array to zero.
struct media_v2_intf_devnode devnode Used only for device node interfaces. See media_v2_intf_devnode for details.
media_v2_intf_devnode
struct media_v2_intf_devnode
__u32 major Device node major number.
__u32 minor Device node minor number.
media_v2_pad
struct media_v2_pad
__u32 id Unique ID for the pad. Do not expect that the ID will always be the same for each instance of the device. In other words, do not hardcode pad IDs in an application.
__u32 entity_id Unique ID for the entity where this pad belongs.
__u32 flags Pad flags, see Media pad flags for more details.
__u32 index Pad index, starts at 0. Only valid if MEDIA_V2_PAD_HAS_INDEX(media_version) returns true. The media_version is defined in struct media_device_info and can be retrieved using ioctl MEDIA_IOC_DEVICE_INFO.
__u32 reserved[4] Reserved for future extensions. Drivers and applications must set this array to zero.
struct media_v2_link
__u32 id Unique ID for the link. Do not expect that the ID will always be the same for each instance of the device. In other words, do not hardcode link IDs in an application.
__u32 source_id

On pad to pad links: unique ID for the source pad.

On interface to entity links: unique ID for the interface.
__u32 sink_id

On pad to pad links: unique ID for the sink pad.

On interface to entity links: unique ID for the entity.
__u32 flags Link flags, see Media link flags for more details.
__u32 reserved[6] Reserved for future extensions. Drivers and applications must set this array to zero.

6.5.5. 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 Generic Error Codes chapter.

ENOSPC
This is returned when either one or more of the num_entities, num_interfaces, num_links or num_pads are non-zero and are smaller than the actual number of elements inside the graph. This may happen if the topology_version changed when compared to the last time this ioctl was called. Userspace should usually free the area for the pointers, zero the struct elements and call this ioctl again.