Re: RFC: Allow Bluez to select flushable or non-flushable ACL packets with L2CAP_LM_RELIABLE

[Marcel Holtmann <marcel@holtmann.org>]

Hi Nick,

> >> Right now Bluez always requests flushable ACL packets (but does not
> >> set a flush timeout, so effectively they are non-flushable):
> >>
> >> However it is desirable to use an ACL flush timeout on A2DP packets so
> >> that if the ACL packets block for some reason then the LM can flush
> >> them to make room for newer packets.
> >>
> >> Is it reasonable for Bluez to use the 0x00 ACL packet boundary flag by
> >> default (non-flushable packet), and let userspace request flushable
> >> packets on A2DP L2CAP sockets with the socket option
> >> L2CAP_LM_RELIABLE.
> >
> > the reliable option has a different meaning. It comes back from the old
> > Bluetooth 1.1 qualification days where we had to tests on L2CAP that had
> > to confirm that we can detect malformed packets and report them. These
> > days it is just fine to drop them.
> 
> Got it, how about introducing
> 
> #define L2CAP_LM_FLUSHABLE 0x0040

that l2cap_sock_setsockopt_old() sets this didn't give you a hint that
we might wanna deprecate this socket options ;)

I need to read up on the flushable stuff, but in the end it deserves its
own socket option. Also an ioctl() to actually trigger Enhanced flush
might be needed.

> struct l2cap_pinfo {
>    ...
>    __u8 flushable;
> }

Sure. In the long run we need to turn this into a bitmask. We are just
wasting memory here.

Regards

Marcel