El Friday 07 May 2010 20:25:17 João Paulo Rechi Vita escribió: > Hello Jose! > > On Fri, May 7, 2010 at 09:08, Gustavo F. Padovan <gustavo@xxxxxxxxxxx> wrote: > > Hi José, > > > > * José Antonio Santos Cadenas <jcaden@xxxxxxxxxxxx> [2010-05-07 13:02:36 +0200]: > > > >> Hi all, > >> > >> I start this thread to discuss the alternatives to move the data from the > >> application to the l2cap socket in HDP. Till now we have the following > >> alternatives (please, add more if we missed something) > >> > >> Reconnections options: > >> > >> Option 1: Implicit reconnections: The application is not concern about the > >> disconnections or reconnections of the data channel until it is deleted. > >> > >> We prefer this option because fixes more with a manager philosophy. A > >> 20601 manager sould not perceive temporal disconnections because this way can > >> hold it state if it perceives a disconnection, next time it reconnects it will > >> need to exchange again apdus for association. > >> > >> Option 2: Reconnections by the application. The applications are notified when > >> a data channel is disconnected and should perform a reconnection before using > >> it again. > >> > > The HDP Implementation Guidance Whitepaper clearly states that > transport (HDP) disconnection / reconnection should be transparent for > the data layer (IEEE 11073-20601), so I guess option 2 here would > break the spec. > > >> Data transmission options: > >> > >> Option 1: Fd_passing the l2cap socket of the data channel to the client. The > >> problem with this is that some data can be lost by d-bus if the channel is > >> disconnected. (We have to check how fd-passing works). > > > > DBus just pass the fd and then don't touch the fd anymore, data can't be > > lost by DBus. > > > > I guess the problem Jose tried to address here is the case that HDP > had temporarily disconnected the data channel and then the application > try to write to the FD (which will be closed). Some data may be lost > by the application on this process. That's exactly what I tried to expose. If you do fd-passing with the l2cap socket, it is possible that the client writes data in a closed socket. If HDP fd-pass a pipe socket, the client will write on the pipe, this way the client perceives just one file descriptor which is exactly what we wanted if reconnections are implicit. > > >> > >> Option 2: Fd_passing a pipe and HDP will write the data in the l2cap data > >> chanel socket. The problem with this is that we need 2 pipes for each data > >> channel, but no data will be lost because HDP controls the data flow with the > >> sockets and resend data not correctly sent. > >> > >> We think that the easier way for implicit reconnections is option 2. > >> Because the application can always write on the socket it have (the pipe). > >> Once written, the HDP layer tries to write it in the l2cap socket, if it > >> fails, perform a reconnection operation over the data channel. > >> > > Considering the drawbacks of the other alternatives and taking into > account that implicit reconnection is the right approach, this seems > the better option. I can't see any problems on having 2 pipes per data > channel, but I personally have never worked with splice directly so I > can't address much issues of this approach. That's the best option for us too. As I said above, this way the client perceives the same socket during the whole live of the connection, perfect for implicit reconnections. > > >> Option 3: Transmiting the data by d-bus. We think that this option is bad for > >> d-bus, because of the overload of the system bus. > > > > Pretty bad ;) > > > > As Gustavo said, transmitting data over d-bus would be very bad. On > some embedded platforms d-bus can be really slow and even for the > desktop case this is unnecessary overhead. > > >> > >> Option 4: Other IPC alternatives (more alternative here?) > >> > > -- To unsubscribe from this list: send the line "unsubscribe linux-bluetooth" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
