tests/image: add booting tests

This commit makes the osbuild-image-tests binary doing the same set of tests
like the old test/run script.

Changes from test/run:
- qemu/nspawn are now killed gracefully. Firstly, SIGTERM is sent.
  If the process doesn't exit till the timeout, SIGKILL is sent.
  I changed this because nspawn leaves some artifacts behind when killed
  by SIGKILL.
- the unsharing of network namespace now works differently because of
  systemd issue #15079

cmd/osbuild-image-tests/netns.go

@@ -0,0 +1,146 @@
+package main
+
+import (
+	"context"
+	"fmt"
+	"io/ioutil"
+	"log"
+	"os"
+	"os/exec"
+	"path"
+	"runtime"
+	"syscall"
+
+	"golang.org/x/sys/unix"
+)
+
+const netnsDir = "/var/run/netns"
+
+// Network namespace abstraction
+type netNS string
+
+// newNetworkNamespace returns a new network namespace with a random
+// name. The calling goroutine remains in the same namespace
+// as before the call.
+func newNetworkNamespace() (netNS, error) {
+	// This method needs to unshare the current thread. Go runtime can switch
+	// the goroutine to run on a different thread at any point, so we need
+	// to ensure that this method runs in the same thread for its whole
+	// lifetime.
+	runtime.LockOSThread()
+	defer runtime.UnlockOSThread()
+
+	_, err := os.Stat(netnsDir)
+
+	if err != nil {
+		if os.IsNotExist(err) {
+			err := os.Mkdir(netnsDir, 0755)
+			if err != nil {
+				return "", fmt.Errorf("cannot create %s: %v", netnsDir, err)
+			}
+		} else {
+			return "", fmt.Errorf("cannot stat %s: %v", netnsDir, err)
+		}
+	}
+
+	f, err := ioutil.TempFile(netnsDir, "osbuild-composer-namespace")
+	if err != nil {
+		return "", fmt.Errorf("cannot create a tempfile: %v", err)
+	}
+
+	// We want to remove the temporary file if the namespace initialization fails.
+	// The best method I could thought of is to have the following variable
+	// denoting if the initialization was successful. It is set to true right
+	// before the end of this function.
+	initOK := false
+	defer func() {
+		if !initOK {
+			err := os.Remove(f.Name())
+			if err != nil {
+				log.Printf("cannot remove the temporary namespace: %v", err)
+			}
+		}
+	}()
+
+	oldNS, err := os.Open("/proc/self/ns/net")
+	if err != nil {
+		return "", fmt.Errorf("cannot open the current namespace: %v", err)
+	}
+
+	err = syscall.Unshare(syscall.CLONE_NEWNET)
+	if err != nil {
+		return "", fmt.Errorf("cannot unshare the network namespace")
+	}
+	defer func() {
+		err = unix.Setns(int(oldNS.Fd()), syscall.CLONE_NEWNET)
+		if err != nil {
+			// We cannot return to the original namespace.
+			// As we don't know nothing about affected threads, let's just
+			// quit immediately.
+			log.Fatalf("returning to the original namespace failed, quitting: %v", err)
+		}
+	}()
+
+	cmd := exec.Command("ip", "link", "set", "up", "dev", "lo")
+	cmd.Stderr = os.Stderr
+	cmd.Stdout = os.Stderr
+	err = cmd.Run()
+	if err != nil {
+		return "", fmt.Errorf("cannot set up a loopback device in the new namespace: %v", err)
+	}
+
+	cmd = exec.Command("mount", "-o", "bind", "/proc/self/ns/net", f.Name())
+	cmd.Stderr = os.Stderr
+	cmd.Stdout = os.Stderr
+	err = cmd.Run()
+	if err != nil {
+		return "", fmt.Errorf("cannot bind mount the new namespace: %v", err)
+	}
+
+	ns := netNS(path.Base(f.Name()))
+
+	// Initialization OK, do not delete the namespace file.
+	initOK = true
+	return ns, nil
+}
+
+// NamespaceCommand returns an *exec.Cmd struct with the difference
+// that it's prepended by "ip netns exec NAMESPACE_NAME" command, which
+// runs the command in a namespaced environment.
+func (n netNS) NamespacedCommand(name string, arg ...string) *exec.Cmd {
+	args := []string{"netns", "exec", string(n), name}
+	args = append(args, arg...)
+	return exec.Command("ip", args...)
+}
+
+// NamespaceCommand returns an *exec.Cmd struct with the difference
+// that it's prepended by "ip netns exec NAMESPACE_NAME" command, which
+// runs the command in a namespaced environment.
+func (n netNS) NamespacedCommandContext(ctx context.Context, name string, arg ...string) *exec.Cmd {
+	args := []string{"netns", "exec", string(n), name}
+	args = append(args, arg...)
+	return exec.CommandContext(ctx, "ip", args...)
+}
+
+// Path returns the path to the namespace file
+func (n netNS) Path() string {
+	return path.Join(netnsDir, string(n))
+}
+
+// Delete deletes the namespaces
+func (n netNS) Delete() error {
+	cmd := exec.Command("umount", n.Path())
+	cmd.Stderr = os.Stderr
+	cmd.Stdout = os.Stdout
+	err := cmd.Run()
+	if err != nil {
+		return fmt.Errorf("cannot unmount the network namespace: %v", err)
+	}
+
+	err = os.Remove(n.Path())
+	if err != nil {
+		return fmt.Errorf("cannot delete the network namespace file: %v", err)
+	}
+
+	return nil
+}