Return-Path: Subject: Re: RFC: Allow Bluez to select flushable or non-flushable ACL packets with L2CAP_LM_RELIABLE From: Marcel Holtmann To: Nick Pelly Cc: linux-bluetooth@vger.kernel.org In-Reply-To: <35c90d960912161548p6cdcc1f0i7d74b31a4bc145b6@mail.gmail.com> References: <35c90d960912081950t135e3f10m8848e54fde1e596f@mail.gmail.com> <1260335175.2901.20.camel@violet> <35c90d960912082213s26fb0ebse75ce85d43213d9@mail.gmail.com> <1260482634.2901.70.camel@violet> <35c90d960912161359u2b3f9b2fi875288896a7a8478@mail.gmail.com> <1261006596.4041.39.camel@localhost.localdomain> <35c90d960912161548p6cdcc1f0i7d74b31a4bc145b6@mail.gmail.com> Content-Type: text/plain; charset="UTF-8" Date: Fri, 18 Dec 2009 15:05:40 -0800 Message-Id: <1261177540.4041.106.camel@localhost.localdomain> Mime-Version: 1.0 Sender: linux-bluetooth-owner@vger.kernel.org List-ID: 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. > >> > >> Attached is an updated patch, that checks the LMP features bitmask > >> before using the new non-flushable packet type. > >> > >> I am still using L2CAP_LM_FLUSHABLE socket option in > >> l2cap_sock_setsockopt_old(), which I don't think you are happy with. > >> So how about a new option: > >> > >> SOL_L2CAP, L2CAP_ACL_FLUSH > >> which has a default value of 0, and can be set to 1 to make the ACL > >> data sent by this L2CAP socket flushable. > > Was this proposal ok? Even SOL_L2CAP goes away. Use SOL_BLUETOOTH for this. > >> In a later commit we would then add > >> SOL_ACL, ACL_FLUSH_TIMEOUT > >> That is used to set an automatic flush timeout for the ACL link on a > >> L2CAP socket. Note that SOL_ACL is new. > > > > can I stop you right here (without even looking at the patch). We do > > have the generic SOL_BLUETOOTH that you should be using. So adding > > SOL_ACL is not a viable option at all. > > This would be in a later patch, and SOL_BLUETOOTH, ACL_FLUSH_TIMEOUT > is fine too, or whatever you prefer. Why not just use BT_FLUSHABLE and have it always take a timeout option and then 0 means not flushable. And advantage of having it separated? Regards Marcel