ap: keep AP beaconing across USB re-enumeration
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
co-authored by
Claude Opus 4.8
Claude Opus 4.8
parent
830ef52641
commit
877fa14d0c
@@ -0,0 +1,20 @@
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# Drop-in: /etc/systemd/system/hostapd.service.d/restart.conf
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#
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# The AP wlan (rtw89, USB) shares a USB hub with the Starlink ethernet (r8152, USB).
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# When Starlink flaps, the hub re-enumerates and the Wi-Fi radio is torn down with it:
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# hostapd's interface vanishes ("No such device") and it exits. Two stock defaults then
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# leave the AP dark until someone intervenes — this drop-in closes both:
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#
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# 1. Restart=on-failure ignores a *clean* exit, but hostapd exits 0 in some of these
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# cases. Restart=always covers every exit.
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# 2. The default start limit (5 starts / 10s) is exhausted by a re-enumeration storm,
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# after which systemd gives up permanently. StartLimitIntervalSec=0 disables the
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# limit so hostapd keeps retrying until the interface comes back.
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[Unit]
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StartLimitIntervalSec=0
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[Service]
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Restart=always
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# A few seconds' backoff so the USB device has a chance to re-enumerate before we retry
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# (retrying instantly just fails on "No such device" and spins).
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RestartSec=5
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@@ -3,6 +3,10 @@ interface=wlxc83a35a4ee55
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# hostapd adds the wlan to the bridge after setting AP mode; the bridge itself + its
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# wired member + the gateway IP are defined under /etc/systemd/network (2x-van-br0/lan).
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bridge=br0
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# Control socket so van-ap-watchdog (and hostapd_cli) can read the AP's real state
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# (state=ENABLED means it's actually beaconing) — used to detect a wedged radio that
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# stays "running" but stops serving after a USB glitch.
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ctrl_interface=/var/run/hostapd
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driver=nl80211
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ssid=VanLink
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country_code=CA
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@@ -0,0 +1,116 @@
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#!/usr/bin/env python3
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"""van-ap-watchdog — keep the VanLink AP beaconing.
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The AP wlan (rtw89, USB) shares a USB hub with the Starlink ethernet (r8152, USB).
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When Starlink's link flaps the hub can re-enumerate and take the Wi-Fi radio down
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with it. The hostapd.service drop-in (restart.conf) handles the common case — hostapd
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exits and systemd restarts it (Restart=always, no start limit) until the interface
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returns. This daemon is the backstop for the case systemd *can't* see: hostapd stays
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running but the radio has wedged and stopped serving (dmesg "timed out to flush queues").
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Every `interval` seconds it asks hostapd for its real state via the control socket
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(hostapd_cli status -> state=ENABLED). If the interface is present but the AP is not
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ENABLED for `fail_threshold` checks in a row, it clears any failed state and restarts
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hostapd. If the interface is simply gone (mid re-enumeration) it waits — there is
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nothing to restart onto, and Restart=always reclaims it when it reappears. Stdlib only.
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"""
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import re
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import subprocess
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import sys
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import time
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from pathlib import Path
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HOSTAPD_CONF = "/etc/hostapd/hostapd.conf"
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CTRL_DIR = "/var/run/hostapd"
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INTERVAL = 15 # seconds between health checks (backstop cadence, not first response)
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FAIL_THRESHOLD = 2 # consecutive bad checks before restarting (debounces re-enum blips)
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def log(msg, level="info"):
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# systemd journal severity prefixes (sd-daemon), same convention as van-thermal.
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pri = {"info": "<6>", "warn": "<4>", "crit": "<2>"}.get(level, "<6>")
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print(pri + msg, flush=True)
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def ap_ifname():
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"""The AP interface name, read from hostapd.conf so there's one source of truth."""
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try:
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for line in Path(HOSTAPD_CONF).read_text().splitlines():
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m = re.match(r"\s*interface=(\S+)", line)
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if m:
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return m.group(1)
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except OSError as e:
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log(f"cannot read {HOSTAPD_CONF} ({e})", "crit")
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return None
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def iface_present(ifname):
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return Path(f"/sys/class/net/{ifname}").exists()
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def ap_enabled(ifname):
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"""True if hostapd reports the AP as beaconing (state=ENABLED). False if it's
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running but not enabled; None if the control socket is unreachable (hostapd down)."""
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try:
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out = subprocess.run(
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["hostapd_cli", "-p", CTRL_DIR, "-i", ifname, "status"],
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capture_output=True, text=True, timeout=10,
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).stdout
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except (OSError, subprocess.SubprocessError) as e:
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log(f"hostapd_cli failed: {e}", "warn")
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return None
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for line in out.splitlines():
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if line.startswith("state="):
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return line.strip() == "state=ENABLED"
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return None # no state line -> couldn't talk to hostapd
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def recover(ifname):
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log(f"AP {ifname} not beaconing — clearing failed state and restarting hostapd", "warn")
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# reset-failed first in case some other path parked the unit in a failed state;
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# harmless when it isn't.
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subprocess.run(["systemctl", "reset-failed", "hostapd"],
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capture_output=True, text=True)
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r = subprocess.run(["systemctl", "restart", "hostapd"],
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capture_output=True, text=True)
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if r.returncode != 0:
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log(f"hostapd restart returned {r.returncode}: {r.stderr.strip()}", "warn")
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def main():
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ifname = ap_ifname()
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if not ifname:
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log("no interface= in hostapd.conf; nothing to watch", "crit")
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sys.exit(1)
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log(f"van-ap-watchdog up: watching {ifname} every {INTERVAL}s "
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f"(restart after {FAIL_THRESHOLD} bad checks)")
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bad = 0
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waiting = False # latch so "interface absent" logs once, not every tick
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while True:
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if not iface_present(ifname):
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if not waiting:
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log(f"{ifname} absent — USB re-enumeration in progress; "
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f"waiting for it to return (hostapd Restart=always will reclaim it)", "warn")
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waiting = True
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bad = 0
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else:
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waiting = False
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if ap_enabled(ifname):
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if bad:
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log(f"AP {ifname} beaconing again")
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bad = 0
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else:
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bad += 1
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if bad >= FAIL_THRESHOLD:
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recover(ifname)
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bad = 0
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time.sleep(INTERVAL)
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if __name__ == "__main__":
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try:
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main()
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except KeyboardInterrupt:
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sys.exit(0)
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@@ -0,0 +1,13 @@
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[Unit]
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Description=VanLink AP watchdog — recover hostapd if the radio wedges after a USB glitch
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After=hostapd.service
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Wants=hostapd.service
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[Service]
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Type=simple
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ExecStart=/usr/local/sbin/van-ap-watchdog
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Restart=always
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RestartSec=5
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[Install]
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WantedBy=multi-user.target
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