Add some notes on mechanics and VFIO kernel driver

README.md

@@ -32,7 +32,9 @@ docker run --cap-add=NET_ADMIN --cap-add=SYS_NICE --cap-add=SYS_PTRACE \
 docker network connect network2 clab-pim
 ```
 
-Note, DPDK will be disabled by default as it requires hugepages and VFIO and/or UIO to use physical
+### A note on DPDK
+
+DPDK will be disabled by default as it requires hugepages and VFIO and/or UIO to use physical
 network cards. If DPDK at some future point is desired, mapping VFIO can be done by adding this:
 ```
            --device=/dev/vfio/vfio:/dev/vfio/vfio
@@ -50,8 +52,25 @@ my-node:
     - /dev/vhost-net
 ```
 
+If using DPDK in a container, one of the userspace IO kernel drivers must be loaded in the host
+kernel. Options are `igb_uio`, `vfio_pci`, or `uio_pci_generic`:
+
+```
+$ sudo modprobe igb_uio
+$ sudo modprobe vfio_pci
+$ sudo modprobe uio_pci_generic
+```
+
+Particularly the VFIO driver needs to be present before one can attempt to bindmount
+`/dev/vfio/vfio` into the container!
+
 ## Configuring VPP
 
+When Containerlab starts the docker containers, it'll offer one or more `vethpair` point to point
+network links, which will show up as `eth1` and further. `eth0` is the default NIC that belongs to
+the management plane in Containerlab (the one which you'll see with `containerlab inspect`). Before
+VPP can use these `vethpair` interfaces, it needs to bind them, like so:
+
 ```
 docker exec -it clab-pim vppctl
 ```
@@ -66,3 +85,8 @@ vpp-clab# set interface ip address eth1 172.19.1.2/24
 vpp-clab# set interface ip address eth1 fec0::2/64
 vpp-clab# set interface state eth1 up
 ```
+
+Containerlab will generate a config file called `/etc/vpp/clab.vpp` which contains all of these
+comands. You can add more commands that'll execute on startup by copying in
+`/etc/vpp/manual-pre.vpp` (to be executed _before_ the containerlab stuff) or
+`/etc/vpp/manual-post.vpp` (to be executed _after_ the containerlab stuff).