bridgemngr: design proposal

bridgemngr/docs/design.md

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+# Bridge manager design proposal
+
+Aim of this document is to propose initial design for bridge manager.
+
+The bridge manager provides flexibility to the user to use the config device section
+or the bridge-vlan section for setting up bridges in the network uci. Essentially,
+this package maps tr181 Device.Bridging.Bridge object to network uci.
+
+# How it works?
+
+The implementation of Bridging.Bridge object is moved to bridgemngr and lauched
+as a microservice.
+
+Please note that the bridgemngr does not have a separate uci for it. It maps to
+network uci, just the way to configure bridges in network uci changes.
+
+We maintain two separate, mutually exclusive implementation of the Bridging.Bridge
+object in the bridgemngr and introduce compile time flags to pick which is selected
+in the build. The proposed options are:
+
+- CONFIG_BRIDGEMNGR_BACKEND_DEVICE (default)
+- CONFIG_BRIDGEMNGR_BACKEND_BRIDGE_VLAN
+
+based on the flag selected, the .so is generated using the corresponding implementation.
+ 
+In case of backend implementation using device, nothing changes, so the UCI for a bridge looks as follows:
+
+```bash
+config device 'l2'
+	option type '8021q'
+	option ifname 'eth2'
+	option vid '100'
+	option name 'eth2.100'
+
+config device 'w100'
+	option type '8021q'
+	option ifname 'eth0'
+	option vid '100'
+	option name 'eth0.100'
+
+config device 'v100'
+	option name 'br-v100'
+	option type 'bridge'
+	list ports 'eth0.100'
+	list ports 'eth2.100'
+
+config device 'i1'
+	option device 'br-v100'
+```
+
+Where as in case of backend implementation using bridge-vlan, it looks as follows:
+
+```bash
+config device 'v100'
+	option name 'br-v100'
+	option type 'bridge'
+	list ports 'eth0'
+	list ports 'eth2'
+
+config bridge-vlan 'v1'
+	option device 'br-v100'
+	option vlan '100'
+	list ports 'eth0:t'
+	list ports 'eth2:t'
+```
+
+# Limitation with bridge-vlan
+
+Please note that the following scenarios cannot be realised with bridge-vlan
+- Managed bridge - device cannot get ip address
+- VLAN Translation
+- The p-bit in header cannot be written at the device so, p-bit translation
+  and setting is possible. The p-bit in the header from the LAN/WAN device
+  is passed on untouched.
+
+Also note that QinQ is possible with bridge-vlans with the uci
+
+```bash
+config device 'vlan100'
+	option name 'br-v100'
+	option type 'bridge'
+	option ports 'eth2'
+
+config device 'eth0_100'
+	option ifname 'eth0'
+	option name 'eth0.100'
+	option vid '100'
+	option type '8021q'
+
+config device 'eth0_200'
+	option ifname 'eth0.100'
+	option name 'eth0.100.200'
+	option vid '200'
+	option type '8021ad'
+
+config bridge-vlan
+	option device 'br-v100'
+	option vlan '100'
+	list ports 'eth2:t'
+	list ports 'eth0.100.200'
+
+config interface 'v100'
+	option device 'br-v100'
+
+```
+
+# Limitations with device backend
+
+Please note that the following limitations exist when device backend is used
+- Traffic prioritization with vlan and p-bit value
+- Preserving the p-bit in the header from LAN/WAN device. The p-bit value
+  is overwritten by the egress_qos_mapping at the vlandev.
+