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ap: keep AP beaconing across USB re-enumeration

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Starlink's USB ethernet shares a hub with the rtw89 Wi-Fi adapter; when Starlink
flaps, the hub re-enumerates and tears the radio down, so hostapd loses its
interface and exits. Two stock defaults left the AP dark: Restart=on-failure
misses clean exits, and the 5-in-10s start limit makes systemd give up during a
re-enumeration storm.

- hostapd-restart.conf drop-in: Restart=always, RestartSec=5, StartLimitIntervalSec=0
  so hostapd retries forever until the interface returns (verified: SIGKILL -> back
  to state=ENABLED in ~7s).
- van-ap-watchdog daemon: backstop for the case systemd can't see (hostapd running
  but radio wedged). Polls hostapd_cli status; restarts hostapd if the iface is
  present but not ENABLED, waits it out if the iface is mid-re-enumeration.
- hostapd.conf: add ctrl_interface so the watchdog can read the real AP state.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
This commit is contained in:
Andreas Wrede
2026-07-01 14:36:14 -04:00
co-authored by Claude Opus 4.8
parent 830ef52641
commit 877fa14d0c
6 changed files with 164 additions and 2 deletions
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README.md
+5 -1
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@@ -37,6 +37,7 @@ This directory is the source of truth. The live system files live under `/etc`,
| WAN interfaces (eth / wifi / gsm), DHCP-client, metrics | **NetworkManager** |
| LAN bridge `br0` + IP (10.42.0.1) + wired LAN member | **systemd-networkd** (`2x-van-br0/lan`) |
| AP beaconing / WPA + adding the wlan to `br0` | **hostapd** (`bridge=br0`; AP iface + wired port are NM-*unmanaged*) |
| Keep the AP beaconing across USB re-enumeration (Starlink flap) | **hostapd** `Restart=always`/no start-limit drop-in + **van-ap-watchdog** daemon (recovers a wedged radio) |
| AP DHCP + DNS | **dnsmasq** (dedicated instance, bound to AP only) |
| NAT + forwarding | **nftables** + sysctl |
| WAN health + failover | **van-failover** daemon |
@@ -64,7 +65,10 @@ This directory is the source of truth. The live system files live under `/etc`,
### `ap/` — access point
| file | → installs to | purpose |
|---|---|---|
| `hostapd.conf` | `/etc/hostapd/hostapd.conf` | AP: SSID `VanLink`, ch149, VHT80/HE, WPA2-PSK, country CA. **WPA passphrase lives here.** |
| `hostapd.conf` | `/etc/hostapd/hostapd.conf` | AP: SSID `VanLink`, ch149, VHT80/HE, WPA2-PSK, country CA, `ctrl_interface` for the watchdog. **WPA passphrase lives here.** |
| `hostapd-restart.conf` | `/etc/systemd/system/hostapd.service.d/restart.conf` | `Restart=always` + `StartLimitIntervalSec=0` so hostapd never gives up after a USB re-enumeration bounces the radio |
| `van-ap-watchdog` | `/usr/local/sbin/van-ap-watchdog` | watches `hostapd_cli status`; restarts hostapd if the radio wedges (running but not `ENABLED`) |
| `van-ap-watchdog.service` | `/etc/systemd/system/van-ap-watchdog.service` | runs the watchdog |
| `default-hostapd` | `/etc/default/hostapd` | `DAEMON_CONF=...` |
| `van-ap-dnsmasq.conf` | `/etc/van-ap/dnsmasq.conf` | DHCP/DNS bound to AP iface (`bind-dynamic`, so it does not clash with systemd-resolved) |
| `van-ap-dnsmasq.service` | `/etc/systemd/system/van-ap-dnsmasq.service` | dedicated dnsmasq unit (uses the `dnsmasq-base` binary; the distro dnsmasq service is NOT used) |