adjusting MapIterator to support also Queues and Stacks + further Que…

…ue-Stack tests + add queue example

1. MapIterator.Next would previously fail with maps of type Queue or Stack, as their Lookup method does not accept a key and acts just like a peek function
2. Add further tests to the Lookup method (peek) with Queue maps, and introduced tests for Stack maps
3. Add example of using Queue within an XDP program

Signed-off-by: Simone Magnani <simonemagnani.96@gmail.com>

examples/README.md

@@ -18,6 +18,7 @@
   * [tcp_close](tcprtt/) - Log RTT of IPv4 TCP connections using eBPF CO-RE helpers.
 * XDP - Attach a program to a network interface to process incoming packets.
   * [xdp](xdp/) - Print packet counts by IPv4 source address.
+  * [queue](queue/) - Print IPv4 Address and Unix Timestamp of each incoming packet.
 * Add your use case(s) here!
 
 ## How to run

examples/queue/main.go

@@ -0,0 +1,115 @@
+// This program demonstrates attaching an eBPF program to a network interface
+// with XDP (eXpress Data Path). The program parses the IPv4 source address
+// from packets and pushes the address alongside the computed packet arrival timestamp
+// into a Queue. This is just an example and probably does not represent the most
+// efficient way to perform such a task. Another potential solution would be to use
+// an HashMap with a small __u64 arrays associated to each IPv4 address (key).
+// In both the two ways it is possible to lose some packet if (a) queue is not large
+// enough or the packet processing time is slow or (b) if the associated array is
+// smaller than the actual received packet from an address.
+// The userspace program (Go code in this file) prints the contents
+// of the map to stdout every second, parsing the raw structure into a human-readable
+// IPv4 address and Unix timestamp.
+// It is possible to modify the XDP program to drop or redirect packets
+// as well -- give it a try!
+// This example depends on bpf_link, available in Linux kernel version 5.7 or newer.
+package main
+
+import (
+	"encoding/binary"
+	"fmt"
+	"log"
+	"net"
+	"net/netip"
+	"os"
+	"strings"
+	"syscall"
+	"time"
+
+	"github.com/cilium/ebpf"
+	"github.com/cilium/ebpf/link"
+)
+
+//go:generate go run github.com/cilium/ebpf/cmd/bpf2go bpf xdp.c -- -I../headers
+
+func main() {
+	if len(os.Args) < 2 {
+		log.Fatalf("Please specify a network interface")
+	}
+
+	// Look up the network interface by name.
+	ifaceName := os.Args[1]
+	iface, err := net.InterfaceByName(ifaceName)
+	if err != nil {
+		log.Fatalf("lookup network iface %q: %s", ifaceName, err)
+	}
+
+	// Load pre-compiled programs into the kernel.
+	objs := bpfObjects{}
+	if err := loadBpfObjects(&objs, nil); err != nil {
+		log.Fatalf("loading objects: %s", err)
+	}
+	defer objs.Close()
+
+	// Attach the program.
+	l, err := link.AttachXDP(link.XDPOptions{
+		Program:   objs.XdpProgFunc,
+		Interface: iface.Index,
+	})
+	if err != nil {
+		log.Fatalf("could not attach XDP program: %s", err)
+	}
+	defer l.Close()
+
+	log.Printf("Attached XDP program to iface %q (index %d)", iface.Name, iface.Index)
+	log.Printf("Press Ctrl-C to exit and remove the program")
+
+	// Retrieve boot time once, and use it for every later ktime conversions
+	bootTime := getSysBoot()
+
+	// Print the contents of the BPF queue (packet source IP address and timestamp).
+	ticker := time.NewTicker(1 * time.Second)
+	defer ticker.Stop()
+	for range ticker.C {
+		s, err := formatMapContents(objs.QueueWithData, bootTime)
+		if err != nil {
+			log.Printf("Error reading map: %s", err)
+			continue
+		}
+		log.Printf("Map contents:\n%s", s)
+	}
+}
+
+// formatMapContents formats an output string with the content of the provided map.
+//
+// For each entry, the function outputs a line containing the human-readable IPv4 address
+// retrieved from the packet structure formatted and the converted ktime_ns into Unix Time
+//
+// In case of error or empty map, the function returns the corresponding error.
+func formatMapContents(m *ebpf.Map, bootTime time.Time) (string, error) {
+	var (
+		sb  strings.Builder
+		val bpfPacketData
+	)
+	iter := m.Iterate()
+	for iter.Next(nil, &val) {
+		// Convert the __u32 into human-readable IPv4
+		a4 := [4]byte{}
+		binary.LittleEndian.PutUint32(a4[:], val.SrcIp)
+		addr := netip.AddrFrom4(a4)
+
+		// Convert ktime timestamp into Time struct, adding the retrieved
+		// timestamp to the previously computer boot time
+		t := bootTime.Add(time.Duration(val.Timestamp) * time.Nanosecond)
+
+		sb.WriteString(fmt.Sprintf("\t%s - %s\n", addr, t))
+	}
+	return sb.String(), iter.Err()
+}
+
+// Retrieve system boot time and convert it into Time struct
+func getSysBoot() time.Time {
+	sysInfo := &syscall.Sysinfo_t{}
+	syscall.Sysinfo(sysInfo)
+	return time.Now().Add(-time.Duration(sysInfo.Uptime) * time.Second)
+}