Fuchsia WLAN Architecture

This directory contains the WLAN stack for Fuchsia. The stack follows a layered architecture, with components interconnected via FIDL.

Layers

1. Policy Layer (wlancfg or wlanix):

   • Role: High-level management, auto-connect logic, network selection, and saved network storage.
   • Exclusivity: Only one of these is present on a given product.
     • wlancfg: Standard Fuchsia WLAN policy. Implements fuchsia.wlan.policy.
     • wlanix: Provides Android-compatible WiFi APIs for Starnix. Implements fuchsia.wlan.wlanix.
   • Interactions: Both interact with wlandevicemonitor to manage interfaces and access the SME.

2. Device Management Layer (wlandevicemonitor):

   • Role: Monitors hardware (PHYs), manages the lifecycle of WLAN interfaces, and bridges policy requests to the appropriate SME.
   • Protocols: Implements fuchsia.wlan.device.service.DeviceMonitor.

3. Core / Stack Layer (SME & MLME):

   • SME (src/connectivity/wlan/lib/sme): Shared logic across all hardware. Manages connection state, scanning, and security (RSN).
   • MLME (src/connectivity/wlan/lib/mlme):
     • SoftMAC: Implemented in host code (mlme/rust). Manages the 802.11 state machine.
     • FullMAC: Implemented as a translation layer (mlme/fullmac). Converts standard MLME commands to vendor-specific fuchsia.wlan.fullmac calls.

4. Driver Layer (drivers/):

   • wlanphy: Management of the physical device.
   • wlansoftmac: Driver that hosts the SoftMAC SME/MLME and implements lower MAC functions.
   • wlanif: Interface protocol between the stack and the driver.

Command Flow: Adding a Feature (e.g., APF)

To plumb a new feature through the stack, follow this flow (using Android Packet Filter (APF) as an example):

1. FIDL Definitions

Define the new types and methods in the appropriate FIDL libraries. See the classification in FIDL.md to determine where your changes belong based on stability and layer boundaries.

2. Policy Layer (wlanix or wlancfg)

• wlanix: Handle requests in src/connectivity/wlan/wlanix/src/main.rs. Use an IfaceManager trait to forward calls to the SME.
• wlancfg: Add logic to state machines (e.g., client/state_machine.rs) to trigger the feature.

3. SME Layer (src/connectivity/wlan/lib/sme)

• Update MlmeRequest enum in lib.rs to include the new command.
• Add methods to ClientSme (e.g., src/client/mod.rs) to send the MlmeRequest.
• Update FIDL request handlers in src/serve/client.rs to call the new SME methods.

4. MLME Layer (src/connectivity/wlan/lib/mlme)

• FullMAC Translation (mlme/fullmac):
  • Add conversion functions in src/convert/mlme_to_fullmac.rs (MLME -> FullMAC) and src/convert/fullmac_to_mlme.rs (FullMAC -> MLME).
  • Update DeviceOps trait and FullmacDevice in src/device.rs to include the new driver calls.
  • Handle the MlmeRequest in the main loop (src/mlme_main_loop.rs), perform the conversion, and call the driver via DeviceOps.

5. Driver Layer

• FullMAC: Implement the new methods in the vendor driver (e.g., brcmfmac).
• SoftMAC: Implement logic in the host-side MLME and wlansoftmac.

Key FIDL Protocols

For a detailed list of key FIDL protocols and their stability guarantees, see FIDL.md.

Testing

• src/connectivity/wlan/testing: Infrastructure like wlantap (virtual driver) and hw-sim.
• src/connectivity/wlan/tests: Integration and E2E tests.