[systemd-devel] [PATCH 00/11] Finalize initial DHCP support

[Marcel Holtmann]

Hi Tom,

>>> The first seven patches fix a few issues with the current code.
>>> 
>>> Patch 09 adds DHCP lease renewing support when timer T1 triggers. Using
>>> the UDP socket sending implementation in patch 08, the DHCP lease
>>> renewal is unicasted to the DHCP server. This means that systemd-network
>>> should have applied the acquired IP address and default route to the
>>> proper interface before timer T1 triggers.
>> 
>> this could become racy and we might end up in funny cases if the lease is really small. I think networkd and the DHCP need some way of communicating a) I set the IP you told me and/or b) we have T1 triggering, have you set the address or should I just redo the DHCP process.
> 
> Makes sense to me for networkd to call (something like)
> sd_dhcp_client_address_configured(client, true) whenever it has
> successfully set the addresses/routes. I.e., I'd go with option (a).
> Or is there a reason to go with (b) that I'm not seeing?

the case I see is that T1 is triggered, but the IP address is not set. Then of course we should not be setting it anymore since it might not stay valid.

However this could be done by DHCP itself just deciding that if client_address_configured is not called by the the time T1 expired, let the DHCP code redo the DHCP discovery.

For good measure we should have warnings in the code for these unlikely race scenarios and see if someone is actually able to trigger them. With ConnMan, I do not recall we had bug reports of this. However we do not know what funny cases happen with virtualization and containers.

Regards

Marcel