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The QoS Policy Propagation via BGP feature allows you to classify packets by IP precedence based on the
Border Gateway Protocol (BGP) community lists, BGP autonomous system paths, access lists, thus helping to
classify based on the destination instead of source address.

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Author: Donald Sharp <[email protected]>
Date:   Mon Apr 19 19:23:45 2021 -0400

1) You need to load the XDP program before starting frr so that
   it can find the LPM map on plugin initialization.
   To keep it simple, the VTY interface was not implemented for now.
   XDP side is accessible via `bpftool`
3) I`m monitoring packets for TOS/DSCP changes to see if marking happens
   But in another approach tag is associated with the packet and then
   read by the TC classifier
4) These are two traffic shaping examples.
   The point is that you have two options for marking:
4.1) Modifying the TOS byte and installing the u32 tc filter to match the value.
   This has a limited range of possible values (8 bits) + needs to modify the packet.
4.2) Using a custom BPF classifier.
    The XDP side extends the packet context and saves the value.
    Afterward, the classifier may read the context and control the shaping behavior
    by setting the `skb->tc_classid` or one of the fields mentioned below.

https://github.com/jestabro/profiling-tools

# NOTE: I had to downgrade this package to resolve the installation conflict
# sudo apt-get install python3-pkg-resources=45.2.0-1
  sudo apt-get install python3-pip
  sudo python3 -m pip install memray
  PATH+=":/home/vyos/.local/bin"

- The boot process has failed, the prompt is stuck, bash is not initialized
- You reboot the device, it tries to read the config, fails once again as there is no free memory
- Config was not loaded, you cannot log in; it is a loop

1. I have removed the global iterator and incapsulated the iteration state into the vty structure.
   This way, each vtysh client has its private iteration state for the following requests.
   It should be possible to query multiple data nodes simultaneously and asynchronously.

1. Stabilization
-  I have seen a corner case that would crash inside the northbound callbacks.
-  I can see some validation failure logs, although the resulting output seems good for me.
-  Daniil was concerned about memory leaks associated with iteration state.
   After additional research - this is not a problem, but I can imagine cases where we would
   fail to handle a malformed XPath and leak resources on the stuck unwinding
   I need to do some testing with Valgrind.
2. Scale testing
3. Async support for multiple vtysh clients. The current demo assumes that there is only one client.
   I want to map the iteration state to the vtysh client/socket so multiple requests may be executed in parallel
4. A debugging instruction
   I have used some complicated debugging flow when merging the feature.
   This should be useful for other (non-C) devs.
5. Finishing the documentation
6. advanced XPath filtering support?

1. The latest proposal draft: 
   Page 72-73 `Retrieve Operational Data - Retrieving Containers and Leaf members`
   Page 84-85 `Retrieve Operational Data - Retrieving Large List elements` + comments
   Page 86 `Retrieve Operational Data - Retrieving Containers and Leaf members` + comments.