'port forced close' after failed ppp

[Colin Helliwell]

> On 13 March 2017 at 09:06 Colin Helliwell <colin.helliwell at ln-systems.com> wrote:
> 
> > On 10 March 2017 at 16:54 Aleksander Morgado <aleksander at aleksander.es> wrote:
> > 
> > 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.
> 
> Tracing in the driver, I can see the TCSETFS ioctl being called at the 'pon' and at the 'poff'. Presumably this *is* from pppd - nothing else is using the port except MM.
> The respective c_cflag values in the args seem to be
>  pon 020000012267
>  poff 016261
> So, yes, it appears that CLOCAL [04000] is being set? (and CRTSCTS cleared)

Using 'local' instead of 'modem' in the ppp settings:
pon  20000014267
poff 016261
i.e. CLOCAL *staying* set, and setting HUPCL?