'port forced close' after failed ppp

[Aleksander Morgado]

On Fri, Mar 10, 2017 at 5:43 PM, Aleksander Morgado
<aleksander at aleksander.es> wrote:
>>> >  mmcli -m 0 --enable
>>> >  mmcli -m 0 --simple-connect="apn=wap.vodafone.co.uk"
>>> >  pon
>>> >  ... success ...
>>> >  poff
>>> >  mmcli -m 0 --simple-disconnect
>>> >
>>> > Then trying again to connect fails with 'forced close'
>>>
>>> I'd consider this an MM bug then. But as a workaround, try passing the
>>> "local" option to pppd, which disables its munging of modem control
>>> lines and thus prevents a port hangup. Does that help?
>>>
>>
>> No, changing 'modem' to 'local' doesn't help.
>> I'm not sure where this hangup is coming from - is it being signalled from the pppd process to MM, or is it that MM is seeing a change on the port lines via the driver? (Would it help if I tried to find out?)
>
> Just to confirm it, could you trace pppd to see if it re-sets CLOCAL
> before exiting?

Some more context...

pppd will by default, unless configured otherwise, unset CLOCAL, which
in turn enables the carrier detect modem control line. pppd uses this
to e.g. detect disconnections reported by the other end. When pppd
exits, it re-sets the serial port configuration to what was found when
the daemon was called. If CLOCAL was set before, pppd will re-set
CLOCAL again.

ModemManager needs to work always with the ports with CLOCAL set (i.e.
ignoring carrier detect).

Some years ago I fixed a bug in NetworkManager which was triggered by
this logic; NM was telling MM that the port was disconnected as soon
as pppd reported "PHASE_DISCONNECT", and MM was taking control of the
port at that time. The problem was that at that time, pppd didn't yet
recover the original serial port configuration, including CLOCAL, so
MM was actually getting the HUP in the TTY right away as carrier
detect was enabled (CLOCAL unset). The fix was to update NM so that it
reports the disconnection to MM only after the DEAD state was reported
by pppd.

So, following what the CLOCAL setting is in the different steps should
definitely help I think.

-- 
Aleksander
https://aleksander.es