// testVM sets up a Go BPF VM, and if available, a native OS BPF VM
// for integration testing.
func testVM(t *testing.T, filter []bpf.Instruction) (virtualMachine, func(), error) {
goVM, err := bpf.NewVM(filter)
if err != nil {
// Some tests expect an error, so this error must be returned
// instead of fatally exiting the test
return nil, nil, err
}
mvm := &multiVirtualMachine{
goVM: goVM,
t: t,
}
// If available, add the OS VM for tests which verify that both the Go
// VM and OS VM have exactly the same output for the same input program
// and packet.
done := func() {}
if canUseOSVM() {
osVM, osVMDone := testOSVM(t, filter)
done = func() { osVMDone() }
mvm.osVM = osVM
}
return mvm, done, nil
}
// testBPFProgram builds a BPF program for the input server and compares the
// output of the program against the input AoE header, returning whether or
// not the header was accepted by the filter.
func testBPFProgram(t *testing.T, s *Server, h *aoe.Header) bool {
filter, ok := bpf.Disassemble(s.mustAssembleBPF(testMTU))
if !ok {
t.Fatal("failed to decode all BPF instructions")
}
vm, err := bpf.NewVM(filter)
if !ok {
t.Fatalf("failed to load BPF program: %v", err)
}
// Fill in empty AoE header fields not relevant to this test
h.Version = aoe.Version
h.Command = aoe.CommandQueryConfigInformation
h.Arg = &aoe.ConfigArg{
Command: aoe.ConfigCommandRead,
}
hb, err := h.MarshalBinary()
if err != nil {
t.Fatalf("failed to marshal AoE header to binary: %v", err)
}
f := ðernet.Frame{
EtherType: aoe.EtherType,
Payload: hb,
}
fb, err := f.MarshalBinary()
if err != nil {
t.Fatalf("failed to marshal Ethernet frame to binary: %v", err)
}
out, err := vm.Run(fb)
if err != nil {
t.Fatalf("failed to run BPF program: %v", err)
}
return out > 0
}
// ExampleNewVM demonstrates usage of a VM, using an Ethernet frame
// as input and checking its EtherType to determine if it should be accepted.
func ExampleNewVM() {
// Offset | Length | Comment
// -------------------------
// 00 | 06 | Ethernet destination MAC address
// 06 | 06 | Ethernet source MAC address
// 12 | 02 | Ethernet EtherType
const (
etOff = 12
etLen = 2
etARP = 0x0806
)
// Set up a VM to filter traffic based on if its EtherType
// matches the ARP EtherType.
vm, err := bpf.NewVM([]bpf.Instruction{
// Load EtherType value from Ethernet header
bpf.LoadAbsolute{
Off: etOff,
Size: etLen,
},
// If EtherType is equal to the ARP EtherType, jump to allow
// packet to be accepted
bpf.JumpIf{
Cond: bpf.JumpEqual,
Val: etARP,
SkipTrue: 1,
},
// EtherType does not match the ARP EtherType
bpf.RetConstant{
Val: 0,
},
// EtherType matches the ARP EtherType, accept up to 1500
// bytes of packet
bpf.RetConstant{
Val: 1500,
},
})
if err != nil {
panic(fmt.Sprintf("failed to load BPF program: %v", err))
}
// Create an Ethernet frame with the ARP EtherType for testing
frame := []byte{
0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
0x00, 0x11, 0x22, 0x33, 0x44, 0x55,
0x08, 0x06,
// Payload omitted for brevity
}
// Run our VM's BPF program using the Ethernet frame as input
out, err := vm.Run(frame)
if err != nil {
panic(fmt.Sprintf("failed to accept Ethernet frame: %v", err))
}
// BPF VM can return a byte count greater than the number of input
// bytes, so trim the output to match the input byte length
if out > len(frame) {
out = len(frame)
}
fmt.Printf("out: %d bytes", out)
// Output:
// out: 14 bytes
}
