adobley · August 24, 2018 18:07 · Aug 24, 2018 · Aug 24, 2018
diff --git a/usage.md b/usage.md
@@ -1,7 +1,7 @@
 We have discovered an potential regression on ubuntu-xenial when upgrading our environments from ubuntu-trusty. 
 The change appears to manifest somewhere between 4.4.0 and 4.15.0 kernel versions.
 
-When listing `bridge fdb` entries via syscalls, we do not recieve any data.
+When listing `bridge fdb` entries via syscalls, we do not receive any data.
 
 We have made a binary that makes the same calls, stripped down to only make the affected calls.
 We are making use of a library to wrap the netlink logic, https://github.com/vishvananda/netlink.

diff --git a/Makefile b/Makefile
@@ -0,0 +1,7 @@
+all: deps build
+
+deps:
+	go get github.com/vishvananda/netlink
+
+build:
+	GOOS=linux GOARCH=amd64 go build
diff --git a/Vagrantfile b/Vagrantfile
@@ -0,0 +1,6 @@
+# -*- mode: ruby -*-
+# vi: set ft=ruby :
+
+Vagrant.configure("2") do |config|
+  config.vm.box = "ubuntu/xenial64"
+end
diff --git a/main.go b/main.go
@@ -0,0 +1,30 @@
+package main
+
+import (
+	"fmt"
+	"os"
+	"strconv"
+	"syscall"
+
+	"github.com/vishvananda/netlink"
+)
+// Call as `./listfdb ${link_index}` to see the entries for the link
+func main() {
+	if len(os.Args) != 2 {
+		panic(fmt.Errorf("you must provide a single index number for the interface you are listing fdb rules for"))
+	}
+
+	index, err := strconv.Atoi(os.Args[1])
+	if err != nil {
+		panic(fmt.Errorf("you must provide an valid index number: %s", err))
+	}
+
+	neighs, err := netlink.NeighList(index, syscall.AF_BRIDGE)
+	if err != nil {
+		panic(fmt.Errorf("list fdb failed: %s", err))
+	}
+
+	for _, neigh := range neighs {
+		fmt.Printf("%#v\n", neigh)
+	}
+}
diff --git a/usage.md b/usage.md
@@ -0,0 +1,29 @@
+We have discovered an potential regression on ubuntu-xenial when upgrading our environments from ubuntu-trusty. 
+The change appears to manifest somewhere between 4.4.0 and 4.15.0 kernel versions.
+
+When listing `bridge fdb` entries via syscalls, we do not recieve any data.
+
+We have made a binary that makes the same calls, stripped down to only make the affected calls.
+We are making use of a library to wrap the netlink logic, https://github.com/vishvananda/netlink.
+
+Steps to reproduce:
+1. install `golang` and `vagrant`
+1. place the `main.go`, `Makefile`, and `Vagrantfile` in `${GOPATH}/src/listfdb`
+1. `cd ${GOPATH}/src/listfdb`
+1. `make` 
+1. `vagrant up` to deploy ubuntu-xenial
+1. `vagrant ssh`
+1. `uname -a` and see that kernel version is `4.4.0`
+1. `bridge fdb` and see that there are entries for `enp0s3`
+1. `ip link` to get the index for `enp0s3`
+1. `/vagrant/listfdb ${link_index}`, 2 should be the index for the `enp0s3` device which has 3 fdb entries by default
+1. `sudo apt-get install linux-image-4.15.0-33-generic -y`
+1. `exit`
+1. `vagrant reload` to restart with `4.15` kernel
+1. `vagrant ssh`
+1. `uname -a` and see that kernel version is `4.15.0`
+1. `bridge fdb` and see that there are entries for `enp0s3`
+1. `ip link` to get the index for `enp0s3`
+1. `/vagrant/listfdb ${link_index}`, 2 should be the index for the `enp0s3` device, note that no results are returned
+
+No entries are listed, despite being able to see them with `bridge fdb`.
No results found