Ah, ok, it was much more complex than what I thought. Thanks for the explanation!
On Mon, Aug 24, 2020, at 20:10, Brennan Ashton wrote: > On Mon, Aug 24, 2020 at 3:56 PM Matias N. <mat...@imap.cc> wrote: > > > That's quite a strange stack arrangement. If you go to the BLE spec, the > > L2CAP sits above the HCI layer. > > I would guess that the arrow between L2CAP and Bluez actually speaks the > > HCI protocol and the "HCI sockets" allow you to directly call into the HCI > > layer. I was under the impression that you wouldn't need to "skip layers" > > to access all functionality of the LL, but I understand then why the > > proposal of exposing the HCI layer via sockets. > > > > The HCI socket interface does not directly map to the HCI interface of the > controller. There are three different channels defined:#define > HCI_CHANNEL_RAW 0 > #define HCI_CHANNEL_RAW 0 > #define HCI_CHANNEL_USER 1 > #define HCI_CHANNEL_MONITOR 2 > #define HCI_CHANNEL_CONTROL 3 > > HCI_CHANNEL_USER removes the rest of the bluetooth stack from the > controller so that you dont have things like the L2CAP interface messing > with the device. This can be super useful, it's actually what I am using > to allow the NuttX sim to control my bluetooth hardware. > This is in contrast to HCI_CHANNEL_RAW which does not unhook the rest of > the stack so you can have multiple things now trying to control the > hardware and you have to be careful. RAW is not recommended anymore. > > HCI_CHANNEL_MONITOR is somewhat self explanatory, but it lets you see all > the transactions that are taking place over the HCI interface (including in > bluez core). This is usually what something like wireshark will use. > HCI_CHANNEL_CONTROL is the "new" control interface that speaks via the > management API. This is what bluetoothd would be using to do things like > advertise a new service. > > I wish this was better documented, but it is scattered around and bits of > knowledge that I picked up writing a bluetooth mesh stack before it was > included in Linux. > > Hopefully that is helpful, > Brennan >
