cmd/fshim/ipc: install signal handler on shim start

Getting killed at this point will result in inconsistent state.

Signed-off-by: Ophestra Umiker <cat@ophivana.moe>

cmd/fshim/ipc/shim/shim.go

@@ -5,6 +5,7 @@ import (
 	"net"
 	"os"
 	"os/exec"
+	"os/signal"
 	"strings"
 	"sync"
 	"sync/atomic"
@@ -128,6 +129,16 @@ func (s *Shim) Start() (*time.Time, error) {
 	}
 	defer func() { killShim() }()
 
+	// take alternative exit path on signal
+	sig := make(chan os.Signal, 2)
+	signal.Notify(sig, syscall.SIGINT, syscall.SIGTERM)
+	go func() {
+		v := <-sig
+		fmsg.Printf("got %s after program start", v)
+		s.killFallback <- nil
+		signal.Ignore(syscall.SIGINT, syscall.SIGTERM)
+	}()
+
 	accept()
 	var conn *net.UnixConn
 	select {

internal/app/start.go

@@ -179,7 +179,11 @@ func (a *app) Wait() (int, error) {
 		// alternative exit path when kill was unsuccessful
 		case err := <-a.shim.WaitFallback():
 			r = 255
+			if err != nil {
 				fmsg.Printf("cannot terminate shim on faulted setup: %v", err)
+			} else {
+				fmsg.VPrintln("alternative exit path selected")
+			}
 		}
 	}