Aleksander Morgado <aleksander@aleksander.es> writes:
> Hey Ian,
>
> On Thu, Oct 12, 2017 at 2:39 PM, Ian Jackson
> <ijackson@chiark.greenend.org.uk> wrote:
>> Aleksander Morgado writes ("Bug#877024: modemmanager should ask before messing with serial ports"):
>>> This is part of the discussion we had in the MM mailing list for such
>>> a solution:
>>> https://lists.freedesktop.org/archives/modemmanager-devel/2017-September/005917.html
>>
>> Thanks, this looks constructive.
>>
>> Of the heuristics in that mail, most seem to me to be very sound
>> justifications for thinking that the device is safe to probe.
>>
>> The one big exception is this:
>>
>> | * If vid is a known modem vendor (e.g. huawei, zte, sierra, u-blox,
>> | telit....), it's a modem and we probe the tty.
>>
>> This is a hostage to the future, since of course we don't know what
>> devices might be manufactured by a particular vendor in the many-years
>> life of a Debian release.
>>
>
> Yes, this one is probably the weakest rule of all. Still not sure at
> which point to apply the rule, though. E.g. should it be applied after
> having applied all the previous rules (in that case it would be a very
> safe rule, maybe totally unneeded) or should it be applied as an OR to
> some other rule (e.g. driver is option/sierra/qcserial OR vendor is
> huawei/zte..., in this case it would be a weaker rule). Will need to
> decide this based on testing with real devices.
It's nice to see that a workable solution seems to be emerging here.
My opinion on the final wrinkle is that for Debian, in the case of
uncertainty, modemmanager should not be probing, and that guessing based
on manufacturer seems insufficiently certain.
Optimistic probing hides the fact that one doesn't _really_ know the
device is a modem. The result being that the bug report mentioning the
features of the device that might allow an improved heuristic to be
developed is never going to be submitted.
That being the case, I agree with Ian that if such behaviour is
implemented, it would be best if it can be disabled at run-time, and that
the Debian package should then default to disabling it.
Having the option to enable it at run-time would still be useful, so
that people that know that they really do have a modem, can:
read the package's README to discover why it doesn't work
report a bug saying what sort of modem they have, and that it's not
being found by the Debian default configuration of MM
and then flick the switch to make modemmanager optimistic enough to
find their modem (on the understanding that it might break other
stuff they could plug in, but at least they'll know why)
Cheers, Phil.
--
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