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Register components with Device Update

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This article shows an example implementation of a Device Update for IoT Hub component enumerator. You can reference this example to implement a custom component enumerator for your IoT devices. A component is an identity beneath the device level that has a composition relationship with the host device.

This article demonstrates a component enumerator using a virtual IoT device called Contoso Virtual Vacuum. Component enumerators are used to implement the proxy update feature.

Proxy update enables updating multiple components on the same IoT device or multiple sensors connected to the IoT device with a single over-the-air deployment. Proxy update supports an installation order for updating components. It also supports multiple-step updating with pre-installation, installation, and post-installation capabilities.

Use cases where proxy updates are applicable include:

  • Targeting specific update files to partitions on the device.
  • Targeting specific update files to apps or components on the device.
  • Targeting specific update files to sensors connected to IoT devices over a network protocol (for example, USB or CAN bus).

For more information, see Proxy updates and multi-component updating.

The Device Update agent runs on the host device. It can send each update to a specific component or to a group of components of the same hardware class (that is, requiring the same software or firmware update).

What is a component enumerator?

A component enumerator is an extension for the Device Update agent that provides information about every component that you need for an over-the-air update via a host device's Azure IoT Hub connection.

The Device Update agent is device and component agnostic. By itself, the agent doesn't know anything about components on (or connected to) a host device at the time of the update.

To enable proxy updates, device builders must identify all the components on the device that can be updated and assign a unique name to each component. Also, a group name can be assigned to components of the same hardware class, so that the same update can be installed onto all components in the same group. Then, the update content handler can install and apply the update to the correct components.

Diagram that shows the proxy update flow.

Here are the responsibilities of each part of the proxy update flow:

  • Device builder

    • Design and build the device.

    • Integrate the Device Update agent and its dependencies.

    • Implement a device-specific component enumerator extension and register with the Device Update agent.

      The component enumerator uses the information from a component inventory or a configuration file to augment static component data (Device Update required) with dynamic data (for example, firmware version, connection status, and hardware identity).

    • Create a proxy update that contains one or more child updates that target one or more components on (or connected to) the device.

    • Send the update to the solution operator.

  • Solution operator

    • Import the update and manifest to the Device Update service.

    • Deploy the update to a group of devices.

  • Device Update agent

    • Get update information from IoT Hub via the device twin or module twin.

    • Invoke a steps handler to process the proxy update intended for one or more components on the device.

      The example in this article has two updates: host-fw-1.1 and motors-fw-1.1. For each child update, the parent steps handler invokes a child steps handler to enumerate all components that match the Compatibilities properties specified in the child update's manifest file. Next, the handler downloads, installs, and applies the child update to all targeted components.

      To get the matching components, the child update calls a SelectComponents API provided by the component enumerator. If there are no matching components, the child update is skipped.

    • Collect all update results from parent and child updates, and report those results to IoT Hub.

  • Child steps handler

    • Iterate through a list of component instances that are compatible with the child update content. For more information, see Steps handler.

In production, device builders can use existing handlers or implement a custom handler that invokes any installer needed for an over-the-air update. For more information, see Implement a custom update content handler.

Virtual Vacuum components

For this article, we use a virtual IoT device to demonstrate the key concepts and features. The Contoso Virtual Vacuum device consists of five logical components:

  • Host firmware
  • Host boot file system
  • Host root file system
  • Three motors (left wheel, right wheel, and vacuum)
  • Two cameras (front and rear)

Diagram that shows the Contoso Virtual Vacuum components.

The following directory structure simulates the components:

/usr/local/contoso-devices/vacuum-1/hostfw
/usr/local/contoso-devices/vacuum-1/bootfs
/usr/local/contoso-devices/vacuum-1/rootfs
/usr/local/contoso-devices/vacuum-1/motors/0   /* left motor */
/usr/local/contoso-devices/vacuum-1/motors/1   /* right motor */
/usr/local/contoso-devices/vacuum-1/motors/2   /* vacuum motor */
/usr/local/contoso-devices/vacuum-1/cameras/0  /* front camera */
/usr/local/contoso-devices/vacuum-1/cameras/1  /* rear camera */

Each component's directory contains a JSON file that stores a mock software version number of each component. Example JSON files are firmware.json and diskimage.json.

For this demo, to update the components' firmware, we'll copy firmware.json or diskimage.json (update payload) to the targeted components' directory.

Here's an example firmware.json file:

{
    "version": "0.5",
    "description": "This component is generated for testing purposes."
}

Note

Contoso Virtual Vacuum contains software or firmware versions for the purpose of demonstrating proxy update. It doesn't provide any other functionality.

Implement a component enumerator (C language)

Requirements

Implement all APIs declared in component_enumerator_extension.hpp:

Function Arguments Returns
char* GetAllComponents() None A JSON string that contains an array of all ComponentInfo values. For more information, see Example return values.
char* SelectComponents(char* selector) A JSON string that contains one or more name/value pairs used for selecting update target components A JSON string that contains an array of ComponentInfo values. For more information, see Example return values.
void FreeComponentsDataString(char* string) A pointer to string buffer previously returned by GetAllComponents or SelectComponents functions None

ComponentInfo

The ComponentInfo JSON string must include the following properties:

Name Type Description
id string A component's unique identity (device scope). Examples include hardware serial number, disk partition ID, and unique file path of the component.
name string A component's logical name. This property is the name that a device builder assigns to a component that's available in every device of the same device class.

For example, every Contoso Virtual Vacuum device contains a motor that drives a left wheel. Contoso assigned left motor as a common (logical) name for this motor to easily refer to this component, instead of hardware ID, which can be globally unique.
group string A group that this component belongs to.

For example, all motors could belong to a motors group.
manufacturer string For a physical hardware component, this property is a manufacturer or vendor name.

For a logical component, such as a disk partition or directory, it can be any device builder's defined value.
model string For a physical hardware component, this property is a model name.

For a logical component, such as a disk partition or directory, this property can be any device builder's defined value.
properties object A JSON object that contains any optional device-specific properties.

Here's an example of ComponentInfo code based on the Contoso Virtual Vacuum components:

{
    "id": "contoso-motor-serial-00000",
    "name": "left-motor",
    "group": "motors",
    "manufacturer": "contoso",
    "model": "virtual-motor",
    "properties": {
        "path": "\/usr\/local\/contoso-devices\/vacuum-1\/motors\/0",
        "firmwareDataFile": "firmware.json",
        "status": "connected",
        "version" : "motor-fw-1.0"
    }
}

Example return values

Following is a JSON document returned from the GetAllComponents function. It's based on the example implementation of the Contoso Virtual Vacuum component enumerator.

{
    "components": [
        {
            "id": "hostfw",
            "name": "hostfw",
            "group": "firmware",
            "manufacturer": "contoso",
            "model": "virtual-firmware",
            "properties": {
                "path": "\/usr\/local\/contoso-devices\/vacuum-1\/hostfw",
                "firmwareDataFile": "firmware.json",
                "status": "ok",
                "version" : "host-fw-1.0"
            }
        },
        {
            "id": "bootfs",
            "name": "bootfs",
            "group": "boot-image",
            "manufacturer": "contoso",
            "model": "virtual-disk",
            "properties": {
                "path": "\/usr\/local\/contoso-devices\/vacuum-1\/bootfs",
                "firmwareDataFile": "diskimage.json",
                "status": "ok",
                "version" : "boot-fs-1.0"
            }
        },
        {
            "id": "rootfs",
            "name": "rootfs",
            "group": "os-image",
            "manufacturer": "contoso",
            "model": "virtual-os",
            "properties": {
                "path": "\/usr\/local\/contoso-devices\/vacuum-1\/rootfs",
                "firmwareDataFile": "diskimage.json",
                "status": "ok",
                "version" : "root-fs-1.0"
            }
        },
        {
            "id": "contoso-motor-serial-00000",
            "name": "left-motor",
            "group": "motors",
            "manufacturer": "contoso",
            "model": "virtual-motor",
            "properties": {
                "path": "\/usr\/local\/contoso-devices\/vacuum-1\/motors\/0",
                "firmwareDataFile": "firmware.json",
                "status": "ok",
                "version" : "motor-fw-1.0"
            }
        },
        {
            "id": "contoso-motor-serial-00001",
            "name": "right-motor",
            "group": "motors",
            "manufacturer": "contoso",
            "model": "virtual-motor",
            "properties": {
                "path": "\/usr\/local\/contoso-devices\/vacuum-1\/motors\/1",
                "firmwareDataFile": "firmware.json",
                "status": "ok",
                "version" : "motor-fw-1.0"
            }
        },
        {
            "id": "contoso-motor-serial-00002",
            "name": "vacuum-motor",
            "group": "motors",
            "manufacturer": "contoso",
            "model": "virtual-motor",
            "properties": {
                "path": "\/usr\/local\/contoso-devices\/vacuum-1\/motors\/2",
                "firmwareDataFile": "firmware.json",
                "status": "ok",
                "version" : "motor-fw-1.0"
            }
        },
        {
            "id": "contoso-camera-serial-00000",
            "name": "front-camera",
            "group": "cameras",
            "manufacturer": "contoso",
            "model": "virtual-camera",
            "properties": {
                "path": "\/usr\/local\/contoso-devices\/vacuum-1\/camera\/0",
                "firmwareDataFile": "firmware.json",
                "status": "ok",
                "version" : "camera-fw-1.0"
            }
        },
        {
            "id": "contoso-camera-serial-00001",
            "name": "rear-camera",
            "group": "cameras",
            "manufacturer": "contoso",
            "model": "virtual-camera",
            "properties": {
                "path": "\/usr\/local\/contoso-devices\/vacuum-1\/camera\/1",
                "firmwareDataFile": "firmware.json",
                "status": "ok",
                "version" : "camera-fw-1.0"
            }
        }
    ]
}

The following JSON document is returned from the SelectComponents function. It's based on the example implementation of the Contoso component enumerator.

Here's the input parameter for selecting the motors component group:

{
    "group" : "motors"
}

Here's the output of the parameter. All components belong to the motors group.

{
    "components": [
        {
            "id": "contoso-motor-serial-00000",
            "name": "left-motor",
            "group": "motors",
            "manufacturer": "contoso",
            "model": "virtual-motor",
            "properties": {
                "path": "\/usr\/local\/contoso-devices\/vacuum-1\/motors\/0",
                "firmwareDataFile": "firmware.json",
                "status": "ok",
                "version" : "motor-fw-1.0"
            }
        },
        {
            "id": "contoso-motor-serial-00001",
            "name": "right-motor",
            "group": "motors",
            "manufacturer": "contoso",
            "model": "virtual-motor",
            "properties": {
                "path": "\/usr\/local\/contoso-devices\/vacuum-1\/motors\/1",
                "firmwareDataFile": "firmware.json",
                "status": "ok",
                "version" : "motor-fw-1.0"
            }
        },
        {
            "id": "contoso-motor-serial-00002",
            "name": "vacuum-motor",
            "group": "motors",
            "manufacturer": "contoso",
            "model": "virtual-motor",
            "properties": {
                "path": "\/usr\/local\/contoso-devices\/vacuum-1\/motors\/2",
                "firmwareDataFile": "firmware.json",
                "status": "ok",
                "version" : "motor-fw-1.0"
            }
        }
    ]
}

Here's the input parameter for selecting a single component named hostfw:

{
    "name" : "hostfw"
}

Here's the parameter's output for the hostfw component:

{
    "components": [
        {
            "id": "hostfw",
            "name": "hostfw",
            "group": "firmware",
            "manufacturer": "contoso",
            "model": "virtual-firmware",
            "properties": {
                "path": "\/usr\/local\/contoso-devices\/vacuum-1\/hostfw",
                "firmwareDataFile": "firmware.json",
                "status": "ok",
                "version" : "host-fw-1.0"
            }
        }
    ]
}

Note

The preceding example demonstrated that, if needed, it's possible to send a newer update to any instance of a component that's selected by name property. For example, deploy the motor-fw-2.0 update to vacuum-motor while continuing to use motor-fw-1.0 on left-motor and right-motor.

Inventory file

The example implementation shown earlier for the Contoso Virtual Vacuum component enumerator will read the device-specific components' information from the component-inventory.json file. This example implementation is only for demonstration purposes.

In a production scenario, some properties should be retrieved directly from the actual components. These properties include id, manufacturer, and model.

The device builder defines the name and group properties. These values should never change after they're defined. The name property must be unique within the device.

Example component-inventory.json file

Note

The content in this file looks almost the same as the returned value from the GetAllComponents function. However, ComponentInfo in this file doesn't contain version and status properties. The component enumerator will populate these properties at runtime.

For example, for hostfw, the value of the property properties.version will be populated from the specified (mock) firmwareDataFile value (/usr/local/contoso-devices/vacuum-1/hostfw/firmware.json).

{
    "components": [
        {
            "id": "hostfw",
            "name": "hostfw",
            "group": "firmware",
            "manufacturer": "contoso",
            "model": "virtual-firmware",
            "properties": {
                "path": "\/usr\/local\/contoso-devices\/vacuum-1\/hostfw",
                "firmwareDataFile": "firmware.json",
            }
        },
        {
            "id": "bootfs",
            "name": "bootfs",
            "group": "boot-image",
            "manufacturer": "contoso",
            "model": "virtual-disk",
            "properties": {
                "path": "\/usr\/local\/contoso-devices\/vacuum-1\/bootfs",
                "firmwareDataFile": "diskimage.json",
            }
        },
        {
            "id": "rootfs",
            "name": "rootfs",
            "group": "os-image",
            "manufacturer": "contoso",
            "model": "virtual-os",
            "properties": {
                "path": "\/usr\/local\/contoso-devices\/vacuum-1\/rootfs",
                "firmwareDataFile": "diskimage.json",
            }
        },
        {
            "id": "contoso-motor-serial-00000",
            "name": "left-motor",
            "group": "motors",
            "manufacturer": "contoso",
            "model": "virtual-motor",
            "properties": {
                "path": "\/usr\/local\/contoso-devices\/vacuum-1\/motors\/0",
                "firmwareDataFile": "firmware.json",
            }
        },
        {
            "id": "contoso-motor-serial-00001",
            "name": "right-motor",
            "group": "motors",
            "manufacturer": "contoso",
            "model": "virtual-motor",
            "properties": {
                "path": "\/usr\/local\/contoso-devices\/vacuum-1\/motors\/1",
                "firmwareDataFile": "firmware.json",
            }
        },
        {
            "id": "contoso-motor-serial-00002",
            "name": "vacuum-motor",
            "group": "motors",
            "manufacturer": "contoso",
            "model": "virtual-motor",
            "properties": {
                "path": "\/usr\/local\/contoso-devices\/vacuum-1\/motors\/2",
                "firmwareDataFile": "firmware.json",
            }
        },
        {
            "id": "contoso-camera-serial-00000",
            "name": "front-camera",
            "group": "cameras",
            "manufacturer": "contoso",
            "model": "virtual-camera",
            "properties": {
                "path": "\/usr\/local\/contoso-devices\/vacuum-1\/camera\/0",
                "firmwareDataFile": "firmware.json",
            }
        },
        {
            "id": "contoso-camera-serial-00001",
            "name": "rear-camera",
            "group": "cameras",
            "manufacturer": "contoso",
            "model": "virtual-camera",
            "properties": {
                "path": "\/usr\/local\/contoso-devices\/vacuum-1\/camera\/1",
                "firmwareDataFile": "firmware.json",
            }
        }
    ]
}

Next steps

The example in this article used C. To explore C++ example source codes, see:

For various sample updates for components connected to the Contoso Virtual Vacuum device, see Proxy update demo.