Re: ModemManager: issues with port probing and cached capabilities

[Aleksander Morgado <aleksander lanedo com>]

> > Most (all?) implementations of grab_port() in the plugins rely on the
> > fact that the port probing task they get as input argument is exactly
> > the one which did the port probing: there are calls to
> > mm_plugin_base_supports_task_get_probed_capabilities() usually in
> > grab_port() in order to know if a GSM or CDMA modem object is to be
> > created. This is even the case for the generic plugin, which means that
> > if some other plugin did the real port probing, once the Generic plugin
> > wants to grab the port (cases 2 and 3 above), the call to
> > mm_plugin_base_supports_task_get_probed_capabilities() will return 0 and
> > the port won't be grabbed, spitting something like:
> >    do_grab_port(): plugin 'Generic' claimed to support tty/ttyUSB0 but
> > couldn't: (-1) (unknown)
> > 
> > I guess this behaviour is undesired, we shouldn't make grab_port()
> > assume that the supports task that gets as input is really the supports
> > task that did the real probing. Or, otherwise, we could try to simulate
> > that a port probing was done by that supports task by copying the cached
> > capabilities within the supports task results. Any other suggestion on
> > how to avoid this issue?
> > 
> 
> I already implemented a fix for this in the 'plugin-cinterion' branch in
> my gitorious.org repo:
> https://gitorious.org/lanedo/modemmanager/commit/1eae72f6c7c89341c16e95f4a7f0fb82fc8ccfc0
> 
> The fix involves changing all plugins so that, in supports_port(), they
> don't call mm_plugin_base_get_cached_port_capabilities (). Instead, they
> call a new mm_plugin_base_supports_task_propagate_cached(). This new
> method will check if already cached probed results are available, and if
> so, it will propagate the cached results to the supports task itself, so
> that if supports_task_get_probed_capabilities() is called afterwards, a
> copy of the cached ones is returned.
> 
> With this fix, a plugin trying to grab a given port does not depend on
> having done the probe itself, as the supports task will always contain
> either a copy of the previously cached results, or the results of a
> newly launched probe.
> 
> Note that the commit above alone is not merge-able in master, as it's
> based on the not-yet-merged cinterion-plugin branch.
> 

This fix is now also in git master, merged along with the Cinterion
plugin changes.

Cheers,

-- 
Aleksander