[review] Support for printing message field contents in debug traces

[Aleksander Morgado]

Hey,

The following MR implements support for printing the message field
contents, in a similar way as done in libqmi.
https://gitlab.freedesktop.org/mobile-broadband/libmbim/merge_requests/1

There is a lot of room for improvement in the codegen code... the
logic is much simpler and uglier than the one in libqmi, but that is
also because the protocol is a bit simpler, and we don't have "arrays
of structs that have themselves other arrays of other structs..." as
in QMI. Being a simpler protocol, the only complication in MBIM is the
separate field-printers when out-of-struct and the field-printers when
in-struct.

Anyway, it works, and I find it extremely handy to debug issues when
e.g. ModemManager is used in debug mode.

A quick example when querying device caps, this is what we now would
see in the debug log:
[07 oct 2018, 22:43:39] [Debug] [/dev/cdc-wdm3] Received message (translated)...
>>>>>> Header:
>>>>>>   length      = 212
>>>>>>   type        = command-done (0x80000003)
>>>>>>   transaction = 3
>>>>>> Fragment header:
>>>>>>   total   = 1
>>>>>>   current = 0
>>>>>> Contents:
>>>>>>   status error = 'None' (0x00000000)
>>>>>>   service      = 'basic-connect' (a289cc33-bcbb-8b4f-b6b0-133ec2aae6df)
>>>>>>   cid          = 'device-caps' (0x00000001)
>>>>>> Fields:
>>>>>>   DeviceType = 'embedded'
>>>>>>   CellularClass = 'gsm'
>>>>>>   VoiceClass = 'no-voice'
>>>>>>   SimClass = 'removable'
>>>>>>   DataClass = 'umts, hsdpa, hsupa, lte, custom'
>>>>>>   SmsCaps = 'pdu-receive, pdu-send'
>>>>>>   ControlCaps = 'reg-manual'
>>>>>>   MaxSessions = '8'
>>>>>>   CustomDataClass = 'HSPA+'
>>>>>>   DeviceId = '863212030078742'
>>>>>>   FirmwareInfo = '18500.5001.00.01.20.72'
>>>>>>   HardwareInfo = 'V1.0.4'

Comments?

-- 
Aleksander
https://aleksander.es