Fix hostapd's place in systemd dependency tree. #45464
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Here is the dependency graph that I get with this PR. Notice that br0-netdev.service depends on network-link-wlp4s0.service which depends on hostapd.service which depends on sys-subsystem-net-devices-wlp4s0.device. You can generate this graph yourself with: |
Mic92
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Aug 22, 2018
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| after = [ "${cfg.interface}-cfg.service" "nat.service" "bind.service" "dhcpd.service" "sys-subsystem-net-devices-${cfg.interface}.device" ]; | ||
| after = [ "sys-subsystem-net-devices-${cfg.interface}.device" ]; | ||
| requiredBy = [ "network-link-${cfg.interface}.service" ]; |
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Maybe it should also add BindsTo=sys-subsystem-net-devices-wlan0.device?
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Arch does After=network.target, but I guess they just cannot add more specific requirements because they don't know which interface will be used.
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Yes, BindsTo seems appropriate. I'll switch after to BindsTo as BindsTo is already implies the effects of after.
after=network.target is not correct, as this potentially would hoist hostapd to the top of the dependency tree and causes the race to reappear. To get a visual idea of that, please look at the pdf attached in my PR comment. Also after=network.target gives a cyclic after chain of hostapd->network->br0-netdev->network-link-wl4s0->hostapd. Somebody in #16090 said they had the same bridge race with Arch. Maybe that's the reason. I'll ping this PR to them.
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@clefru your patch does not work here probosed solutionmerge our patches as this: i've tried with these configs seem to use a combination of
with only your patchpatch: outcome: journalctl -u hostapd then it works with our patches combinedboot log: journalctl -u hostapd |
* nat/bind/dhcp.service:
Remove. Those services have nothing to do with a link-level service.
* sys-subsystem-net-devices-${if}.device:
Add as BindsTo dependency as this will make hostapd stop when the
device is unplugged.
* network-link-${if}.service:
Add hostapd as dependency for this service via requiredBy clause,
so that the network link is only considered to be established
only after hostapd has started.
* network.target:
Remove this from wantedBy clause as this is already implied from
dependencies stacked above hostapd. And if it's not implied than
starting hostapd is not required for this particular network
configuration.
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@qknight I have updated the PR as you suggested (retaining the after clause). Thanks for you analysis. (Also I reread the systemd.unit manpage, and my assertation above that "BindsTo" effects subsume those of "after" is wrong, hence it's still needed) |
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@clefru ok, when you think the PR is ready i evaluate it once more, then we merge |
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@qknight Please re-evaluate the PR as I updated it with your suggestions. Thank you! |
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* nat/bind/dhcp.service:
Remove. Those services have nothing to do with a link-level service.
* sys-subsystem-net-devices-${if}.device:
Add as BindsTo dependency as this will make hostapd stop when the
device is unplugged.
* network-link-${if}.service:
Add hostapd as dependency for this service via requiredBy clause,
so that the network link is only considered to be established
only after hostapd has started.
* network.target:
Remove this from wantedBy clause as this is already implied from
dependencies stacked above hostapd. And if it's not implied than
starting hostapd is not required for this particular network
configuration.
(cherry picked from commit 725fcde)
Mic92
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Oct 17, 2018
Fix hostapd's place in systemd dependency tree. (#45464)
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This broke hostapd when using systemd-networkd, because |
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after clause:
requiredBy clause:
wantedBy clause:
stacked above hostapd. And if it's not implied than starting hostapd is not required
for this particular network configuration.
Motivation for this change
bridge setup races with hostapd, and if it wins, the bridge fails to start, see: #16090
Things done
sandboxinnix.confon non-NixOS)nix-shell -p nox --run "nox-review wip"./result/bin/)nix path-info -Sbefore and after)