Fixups for stopping gvproxy

Paul found logic errors in my earlier code for finding processes and
sending signals.  Some of the logic errors are associated with how
methods behave on different operating systems.  Created a darwin and
linux approach and a windows approach.

Signed-off-by: Brent Baude <bbaude@redhat.com>

[NO NEW TESTS NEEDED]

pkg/machine/gvproxy.go

@@ -2,7 +2,6 @@ package machine
 
 import (
 	"fmt"
-	"os"
 	"strconv"
 	"syscall"
 	"time"
@@ -19,7 +18,7 @@ const (
 func backoffForProcess(pid int) error {
 	sleepInterval := sleepTime
 	for i := 0; i < loops; i++ {
-		proxyProc, err := os.FindProcess(pid)
+		proxyProc, err := findProcess(pid)
 		if proxyProc == nil && err != nil {
 			// process is killed, gone
 			return nil //nolint: nilerr
@@ -35,13 +34,16 @@ func backoffForProcess(pid int) error {
 // process to not exist.  if the sigterm does not end the process after an interval,
 // then sigkill is sent.  it also waits for the process to exit after the sigkill too.
 func waitOnProcess(processID int) error {
-	proxyProc, err := os.FindProcess(processID)
+	proxyProc, err := findProcess(processID)
 	if err != nil {
 		return err
 	}
 
 	// Try to kill the pid with sigterm
 	if err := proxyProc.Signal(syscall.SIGTERM); err != nil {
+		if err == syscall.ESRCH {
+			return nil
+		}
 		return err
 	}
 
@@ -50,14 +52,16 @@ func waitOnProcess(processID int) error {
 	}
 
 	// sigterm has not killed it yet, lets send a sigkill
-	proxyProc, err = os.FindProcess(processID)
+	proxyProc, err = findProcess(processID)
 	if proxyProc == nil && err != nil {
 		// process is killed, gone
 		return nil //nolint: nilerr
 	}
 	if err := proxyProc.Signal(syscall.SIGKILL); err != nil {
-		// lets assume it is dead in this case
-		return nil //nolint: nilerr
+		if err == syscall.ESRCH {
+			return nil
+		}
+		return err
 	}
 	return backoffForProcess(processID)
 }
@@ -72,8 +76,8 @@ func CleanupGVProxy(f VMFile) error {
 	if err != nil {
 		return fmt.Errorf("unable to convert pid to integer: %v", err)
 	}
-	if err := waitOnProcess(proxyPid); err == nil {
-		return nil
+	if err := waitOnProcess(proxyPid); err != nil {
+		return err
 	}
 	return f.Delete()
 }

pkg/machine/gvproxy_unix.go

@@ -0,0 +1,24 @@
+//go:build darwin || dragonfly || freebsd || linux || netbsd || openbsd
+// +build darwin dragonfly freebsd linux netbsd openbsd
+
+package machine
+
+import (
+	"os"
+	"syscall"
+)
+
+func findProcess(pid int) (*os.Process, error) {
+	p, err := os.FindProcess(pid)
+	if err != nil {
+		return nil, err
+	}
+	// On unix, findprocess will always return a process even
+	// if the process is not found.  you must send a 0 signal
+	// to the process to see if it is alive.
+	// https://pkg.go.dev/os#FindProcess
+	if err := p.Signal(syscall.Signal(0)); err != nil {
+		return nil, err
+	}
+	return p, nil
+}

pkg/machine/gvproxy_windows.go

@@ -0,0 +1,10 @@
+//go:build windows
+// +build windows
+
+package machine
+
+import "os"
+
+func findProcess(pid int) (*os.Process, error) {
+	return os.FindProcess(pid)
+}