internal/netlink: wrap netpoll via context

This removes netpoll boilerplate for the most common use case.

Signed-off-by: Ophestra <cat@gensokyo.uk>

container/dispatcher.go

@@ -1,6 +1,7 @@
 package container
 
 import (
+	"context"
 	"io"
 	"io/fs"
 	"net"
@@ -66,7 +67,7 @@ type syscallDispatcher interface {
 	// ensureFile provides ensureFile.
 	ensureFile(name string, perm, pperm os.FileMode) error
 	// mustLoopback provides mustLoopback.
-	mustLoopback(msg message.Msg)
+	mustLoopback(ctx context.Context, msg message.Msg)
 
 	// seccompLoad provides [seccomp.Load].
 	seccompLoad(rules []std.NativeRule, flags seccomp.ExportFlag) error
@@ -170,7 +171,7 @@ func (k direct) mountTmpfs(fsname, target string, flags uintptr, size int, perm
 func (direct) ensureFile(name string, perm, pperm os.FileMode) error {
 	return ensureFile(name, perm, pperm)
 }
-func (direct) mustLoopback(msg message.Msg) {
+func (direct) mustLoopback(ctx context.Context, msg message.Msg) {
 	var lo int
 	if ifi, err := net.InterfaceByName("lo"); err != nil {
 		msg.GetLogger().Fatalln(err)
@@ -199,11 +200,14 @@ func (direct) mustLoopback(msg message.Msg) {
 			msg.GetLogger().Fatalf("RTNETLINK answers: %v", err)
 
 		default:
-			msg.GetLogger().Fatalf("RTNETLINK answers with malformed message")
+			if err == context.DeadlineExceeded || err == context.Canceled {
+				msg.GetLogger().Fatalf("interrupted RTNETLINK operation")
+			}
+			msg.GetLogger().Fatal("RTNETLINK answers with malformed message")
 		}
 	}
-	must(c.SendNewaddrLo(uint32(lo)))
-	must(c.SendIfInfomsg(syscall.RTM_NEWLINK, 0, &syscall.IfInfomsg{
+	must(c.SendNewaddrLo(ctx, uint32(lo)))
+	must(c.SendIfInfomsg(ctx, syscall.RTM_NEWLINK, 0, &syscall.IfInfomsg{
 		Family: syscall.AF_UNSPEC,
 		Index:  int32(lo),
 		Flags:  syscall.IFF_UP,

container/dispatcher_test.go

@@ -2,6 +2,7 @@ package container
 
 import (
 	"bytes"
+	"context"
 	"fmt"
 	"io"
 	"io/fs"
@@ -468,7 +469,7 @@ func (k *kstub) ensureFile(name string, perm, pperm os.FileMode) error {
 		stub.CheckArg(k.Stub, "pperm", pperm, 2))
 }
 
-func (*kstub) mustLoopback(message.Msg) { /* noop */ }
+func (*kstub) mustLoopback(context.Context, message.Msg) { /* noop */ }
 
 func (k *kstub) seccompLoad(rules []std.NativeRule, flags seccomp.ExportFlag) error {
 	k.Helper()

container/init.go

@@ -7,6 +7,7 @@ import (
 	"log"
 	"os"
 	"os/exec"
+	"os/signal"
 	"path"
 	"slices"
 	"strconv"
@@ -175,7 +176,11 @@ func initEntrypoint(k syscallDispatcher, msg message.Msg) {
 	}
 
 	if !params.HostNet {
-		k.mustLoopback(msg)
+		ctx, cancel := signal.NotifyContext(context.Background(), CancelSignal,
+			os.Interrupt, SIGTERM, SIGQUIT)
+		defer cancel() // for panics
+		k.mustLoopback(ctx, msg)
+		cancel()
 	}
 
 	// write uid/gid map here so parent does not need to set dumpable