zfscmd: fix nil deref in waitPostLogging when command was killed

fixes #301

zfs/zfscmd/zfscmd_logging.go

@@ -1,6 +1,7 @@
 package zfscmd
 
 import (
+	"os/exec"
 	"time"
 )
 
@@ -28,10 +29,22 @@ func waitPreLogging(c *Cmd, now time.Time) {
 }
 
 func waitPostLogging(c *Cmd, err error, now time.Time) {
+
+	var total, system, user float64
+
+	total = c.Runtime().Seconds()
+	if ee, ok := err.(*exec.ExitError); ok {
+		system = ee.ProcessState.SystemTime().Seconds()
+		user = ee.ProcessState.UserTime().Seconds()
+	} else {
+		system = -1
+		user = -1
+	}
+
 	log := c.log().
-		WithField("total_time_s", c.Runtime().Seconds()).
-		WithField("systemtime_s", c.cmd.ProcessState.SystemTime().Seconds()).
-		WithField("usertime_s", c.cmd.ProcessState.UserTime().Seconds())
+		WithField("total_time_s", total).
+		WithField("systemtime_s", system).
+		WithField("usertime_s", user)
 
 	if err == nil {
 		log.Info("command exited without error")

zfs/zfscmd/zfscmd_platform_test.go

@@ -1,7 +1,9 @@
 package zfscmd
 
 import (
+	"bufio"
 	"bytes"
+	"context"
 	"io"
 	"os/exec"
 	"testing"
@@ -58,3 +60,30 @@ func TestCmdStderrBehaviorStdoutPipe(t *testing.T) {
 	require.True(t, ok)
 	require.Empty(t, ee.Stderr) // !!!!! probably not what one would expect if we only redirect stdout
 }
+
+func TestCmdProcessState(t *testing.T) {
+
+	ctx, cancel := context.WithCancel(context.Background())
+	defer cancel()
+	cmd := exec.CommandContext(ctx, "bash", "-c", "echo running; sleep 3600")
+	stdout, err := cmd.StdoutPipe()
+	require.NoError(t, err)
+	err = cmd.Start()
+	require.NoError(t, err)
+
+	r := bufio.NewReader(stdout)
+	line, err := r.ReadString('\n')
+	require.NoError(t, err)
+	require.Equal(t, "running\n", line)
+
+	// we know it's running and sleeping
+	cancel()
+	err = cmd.Wait()
+	t.Logf("wait err %T\n%s", err, err)
+	require.Error(t, err)
+	ee, ok := err.(*exec.ExitError)
+	require.True(t, ok)
+	require.NotNil(t, ee.ProcessState)
+	require.Contains(t, ee.Error(), "killed")
+
+}