[PATCH] libmbim: Add mbim-proxy support

[Aleksander Morgado]

On Thu, May 29, 2014 at 9:15 PM, Greg Suarez <gpsuarez2512 at gmail.com> wrote:
>> Yes. If we get an indication from the device an there wasn't *any*
>> client configured to receive it, then we should forward it to
>> everyone.
>>
>
> So now that I've implemented this I've come to realize that there's no way
> to tell the difference between
> "there's no client configured to receive an indication" vs "a client that's
> configured to not receive any indications
> from a service"
>

If I understood it correctly, by default clients will start like this:
 * Enabled to receive all indications from standard services (those
defined by MBIM standard).
 * Disabled to receive any indication from non-standard services.

Now, the issue is that the configuration of the service subscribe list
is performed by passing a list of these types:

typedef struct {
    MbimUuid device_service_id;
    guint32 cids_count;
    guint32 *cids;
} MbimEventEntry;

The client will notify which are the CIDs in a given service for which
it wants to get notifications. The client needs to provide the full
list of CIDs per service; those not provided in the list of CIDs are
to be considered disabled.

So, as soon as a client sends
MBIM_CID_BASIC_CONNECT_DEVICE_SERVICE_SUBSCRIBE_LIST, the modem will
(should) only provide indications for the CIDs listed there. The task
of the proxy, therefore is to track which CIDs were enabled by each
client, and build its own
MBIM_CID_BASIC_CONNECT_DEVICE_SERVICE_SUBSCRIBE_LIST with the mixed
lists of CIDs from all clients.

Regarding your point, yes, it is tricky. If we have e.g. 3 clients and
all of them used MBIM_CID_BASIC_CONNECT_DEVICE_SERVICE_SUBSCRIBE_LIST
with an empty list (so that they request not to receive any
notification), and still we get a notification from the device, I
really believe we should still forward it to all clients. Same if we
had 3 clients each with its own list and we get a notification which
is not in any list; we should still forward it to all clients. I'm not
sure whether the proxy should try to 'fix' a wrong behavior of the
modem, if it ever happens. Sure, this logic may never be used if all
modems do it correctly, but not sure. Anyway, I have mixed feelings
about this...

So, what I'm suggesting is the following:

> So what I'm doing is if a client has sent the
> MBIM_CID_BASIC_CONNECT_DEVICE_SERVICE_SUBSCRIBE_LIST
> it will only receive indications from that list.

Yes, unless there is an indication coming which isn't by default
enabled in any client. If there is an indication not configured by any
client, then it should go to all. Clients need to be prepared to
receive indications they didn't ask for (as in no crash, just ignore
them).

> A client will receive all indications if the client has never sent the
> MBIM_CID_BASIC_CONNECT_DEVICE_SERVICE_SUBSCRIBE_LIST
> command or sends the command with no elements, which clears out the list.

If the client has never sent the SUBSCRIBE_LIST command, it should
always get the indications for the standard services. If it sends the
command with no elements, shouldn't we assume that it is trying to
disable all indications?


-- 
Aleksander
https://aleksander.es