Hi Waldo,

> 
> Currently the modem driver acknowledges the PDU right away. If there was a
>  notification back to the modem driver, the PDU acknowledgement could be
>  delayed till that point in time. If something bad happens in between,
>  either the modem or the network can hold on to the PDU and redeliver once
>  oFono is up and running again.
> 
> Looking at at_cmt_notify() the current implementation might have that
>  affect already, as AT+CNMA is only send after calling
>  ofono_sms_deliver_notify(). So as long as ofono_sms_deliver_notify() is
>  handled synchronously and ensures that the PDU is stored one way or
>  another before returning, it will work in case of a crash. (Would like to
>  see assumptions like that called out in the code) That said, if your
>  storage has issues (disk full?) there is currently no way to let the modem
>  driver know that delivery was unsuccessful.

You described the current implementation perfectly.  The driver can assume 
that the fragment has been stored after the call to sms_deliver_notify has 
returned.  For its part, the history plugin should ensure the storage is 
synced when any of the callbacks are called.

I freely admit the lack of documentation, and if this is a comment you want to 
add in the driver definition file I would gladly accept it.  However, up to this 
point we've only had a single driver for SMS and it gets this part right.

The disk full case we're aware of.  Again, this can easily be avoided or 
minimized by notifying the user of such conditions in advance.  This was an 
important use case for devices with 512K of storage, much less so for devices 
with 64GB of storage.

Regards,
-Denis