Re: [PATCH] Bluetooth: Allow SCO/eSCO packet type selection for outgoing SCO connections.

[Marcel Holtmann <marcel@holtmann.org>]

Hi Nick,

> >> As a first step, can we get consensus on the userspace API:
> >>
> >> --- a/include/net/bluetooth/hci.h
> >> +++ b/include/net/bluetooth/hci.h
> >> @@ -139,8 +139,11 @@ enum {
> >> +#define ALL_SCO_PKTS   (SCO_ESCO_MASK | EDR_ESCO_MASK)
> >> +#define ALL_ESCO_PKTS  (SCO_ESCO_MASK | ESCO_EV3 | ESCO_EV4 | ESCO_EV5)
> >>
> >> --- a/include/net/bluetooth/sco.h
> >> +++ b/include/net/bluetooth/sco.h
> >> @@ -37,6 +37,7 @@
> >> struct sockaddr_sco {
> >>       sa_family_t     sco_family;
> >>       bdaddr_t        sco_bdaddr;
> >> +       __u16           sco_pkt_type;
> >> };
> >>
> >> This will at least unblock my work.
> >
> > Would it be better to add new sockopt for sco socket?
> 
> What advantage does that have?
> 
> Putting it in struct sockaddr_sco seems to make more sense since
> packet types can only be selected during SCO connection establishment.
> They can't be changed once the socket is connected.

in theory you can change the allowed packet types for ACL, SCO and eSCO
after the connection is active. However the usefulness here is fairly
limited. In case of ACL it is purely academical and most link manager
will just ignore you. Mainly because the host stack can't really make a
good decision here anyway.

Personally I think it is a total brain dead concept to give this into
the control of the host stack anyway. For eSCO packet types this make a
bit more sense since you might wanna control the bandwidth. However
changing them later is just pointless. And I don't recall of any profile
actually mentioning about it. I think they had a great idea behind eSCO
support, but since it is impossible to get the negotiation parts right,
everybody sticks with simple eSCO channels and doesn't bother to change
them.

And even if we would be going for a setsockopt(), that would be blocking
and then again pretty much pointless API. The sockaddr is most logical
thing that fits into what we wanna achieve. Disallow/allow certain
packet types and essentially force SCO over eSCO.

Regards

Marcel