Imported fix for orphan (dead) processed from ctrox#85.

Author: pruiz

cmd/s3driver/main.go

@@ -21,7 +21,9 @@ import (
 	"fmt"
 	"log"
 	"os"
+	"os/signal"
 	"strings"
+	"syscall"
 
 	"github.com/ctrox/csi-s3/pkg/driver"
 )
@@ -50,6 +52,38 @@ var (
 func main() {
 	flag.Parse()
 
+	// We're running in the container as PID-1 which gets some special
+	// treatment by the kernel. In particular, if a process in the container
+	// terminates and there are still active child processes, the kernel will move
+	// those orphaned processes to be child processes of PID-1 and signal it
+	// by sending a SIGCHLD. Init-systems are expected to handle this case by
+	// reaping those "orphan" processes once they exit.
+	//
+	// Since all available mounters are instructed to daemonize, we need to reap
+	// the daemonized processes since their parent (the mounter) exists once the daemon
+	// is running.
+	go func() {
+		ch := make(chan os.Signal, 1)
+
+		signal.Notify(ch, syscall.SIGCHLD)
+
+		for range ch {
+			var status syscall.WaitStatus
+			pid, err := syscall.Wait4(-1, &status, 0, nil)
+			if err != nil {
+				// we might receive ECHILD when the mounter exits after daemonizing.
+				// We'll be late calling Wait4 here as that process is already reaped
+				// since we're using exec.Command().Run() which already calls Waitpid
+				if val, ok := err.(syscall.Errno); !ok || val != syscall.ECHILD {
+					log.Printf("failed to call wait4: %s\n", err)
+				}
+
+			} else {
+				log.Printf("repeated child %d: status=%d\n", pid, status.ExitStatus())
+			}
+		}
+	}()
+
 	driver, err := driver.New(*nodeID, *endpoint, segments)
 	if err != nil {
 		log.Fatal(err)