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udev: Add documentation of groupRecursive option #64

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Apr 16, 2023
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udev: Add documentation of groupRecursive option #64

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32 changes: 32 additions & 0 deletions docs/discovery-handlers/udev.md
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Original file line number Diff line number Diff line change
Expand Up @@ -21,6 +21,7 @@ Discovery Handlers are passed discovery details that are set in a Configuration
| Helm Key | Value | Default | Description |
| :--- | :--- | :--- | :--- |
| udev.configuration.discoveryDetails.udevRules | array of udev rules | empty | udev rule [supported by the udev Discovery Handler](#udev-rule-format) |
| udev.configuration.discoveryDetails.groupRecursive | boolean | false | If set to true, group devices with a matching parent |

The udev Discovery Handler parses the udev rules listed in a Configuration, searches for them using udev, and returns a list of discovered device nodes (ie: /dev/video0). It parses the udev rules via a grammar [grammar](https://github.com/project-akri/akri/blob/main/discovery-handlers/udev/src/udev_rule_grammar.pest) Akri has created. It expects the udev rules to be formatted according to the [Linux Man pages](https://linux.die.net/man/7/udev).

Expand Down Expand Up @@ -225,6 +226,37 @@ helm install akri akri-helm-charts/akri \

Akri has provided further documentation on [modifying the broker PodSpec](../user-guide/customizing-an-akri-installation.md#modifying-the-brokerpodspec), [instanceServiceSpec, or configurationServiceSpec](../user-guide/customizing-an-akri-installation.md#modifying-instanceservicespec-or-configurationservicespec) More information about how to modify an installed Configuration, add additional Configurations to a cluster, or delete a Configuration can be found in the [Customizing an Akri Installation document](../user-guide/customizing-an-akri-installation.md).

## Grouping related device nodes

Akri currently provides a way to group device nodes under the topmost matching node, this allows to handle a complex device with multiple device nodes as one Instance.

For example with the following udev device tree and the rule `ENV{ID_SERIAL}=="Great Vendor Complex Camera"`:
```
root
├── P: /devices/root/device1
│ A: vendor=Great Vendor
│ E: ID_SERIAL=Great Vendor Complex Camera
│   ├── P: /devices/root/device1/video4linux/video0
│ │ A: vendor=Great Vendor
│ │ E: ID_SERIAL=Great Vendor Complex Camera
│ │ E: DEVNAME=/dev/video0
│   ├── P: /devices/root/device1/video4linux/video1
│ │ A: vendor=Great Vendor
│ │ E: ID_SERIAL=Great Vendor Complex Camera
│ │ E: DEVNAME=/dev/video1
│   └── P: /devices/root/device1/sound/card0/pcmC0D0c
│ A: vendor=Great Vendor
│ E: ID_SERIAL=Great Vendor Complex Camera
│ E: DEVNAME=/dev/snd/pcmC0D0c
└── P: /devices/root/device2
A: vendor=Another Vendor
```
This would result in a single instance grouping `video0`, `video1` and `pcmC0D0c`.

All the device nodes will get mounted into the broker pod and will be listed in the environment variables with `UDEV_DEVNODE` prefix

This behavior can be enabled by setting the `udev.configuration.discoveryDetails.groupRecursive` to `true`.

## Implementation details

The udev implementation can be understood by looking at several things:
Expand Down