mbim-proxy vs mbimcli --no-open/--no-close

[Bjørn Mork]

Aleksander Morgado <aleksander at aleksander.es> writes:

> Hey Greg & others.
>
> One thing we didn't think about is how the mbim-proxy should handle
> --no-open or --no-close actions performed by the mbimcli command line
> interface.
>
>  * When the --no-close option is used by mbimcli, it won't send a last
> MBIM Close request to the modem before exiting.
>
>  * When the --no-open is used by mbimcli, it won't send an initial
> MBIM Open request to the modem when starting (e.g. if --no-close was
> used in the previous action).
>
> Now, when using the proxy, it will send an explicit MBIM Close request
> to the device when all clients have been disconnected from the proxy,
> which prevents the usage of --no-close. How can we best handle this
> situation?
>
> One option would be to let the proxy keep an 'open count' value,
> depending on the open/close requests coming from the clients, and only
> if the open count drops to zero it will send the MBIM close. One
> problem with this approach is that if e.g. we get ModemManager
> segfault unexpectedly it won't send the MBIM close, so an
> open-reference will be lost. Not sure if this is a big issue, though.
>
> What do people think?

I don't think there is any way you can make CLOSE work with the proxy,
so you might as well just do an OPEN when the proxy starts and a CLOSE
when it exits.

The only reason a client has to close a session is to ensure that the
modem is reset to some default initial state.  This is impossible to
gurarantee with the proxy, because other clients may depend on the
current state.  IMHO it is better to make the behaviour predictable by
never honouring a CLOSE request than to implement some scheme to allow
the last client to issue a real CLOSE.

And it is easier as well :-) No reference counter and no problems with
crashing clients.


Bjørn