Rework calls to panic into bubbled-up errors

Rather than panicing, bubble up an error such that
the execution may recover correctly.

Signed-off-by: Christopher Obbard <[email protected]>

commands.go

@@ -209,7 +209,11 @@ func (cmd *Command) restoreResolvConf(sum *[sha256.Size]byte) error {
 }
 
 func (cmd Command) Run(label string, cmdline ...string) error {
-	q := newQemuHelper(cmd)
+	q, err := newQemuHelper(cmd)
+	if err != nil {
+		return err
+	}
+
 	q.Setup()
 	defer q.Cleanup()
 
@@ -282,11 +286,11 @@ type qemuHelper struct {
 	qemutarget string
 }
 
-func newQemuHelper(c Command) qemuHelper {
+func newQemuHelper(c Command) qemuHelper, error {
 	q := qemuHelper{}
 
 	if c.Chroot == "" || c.Architecture == "" {
-		return q
+		return q, nil
 	}
 
 	switch c.Architecture {
@@ -305,14 +309,14 @@ func newQemuHelper(c Command) qemuHelper {
 	case "amd64", "i386":
 		/* Dummy, no qemu */
 	default:
-		log.Panicf("Don't know qemu for Architecture %s", c.Architecture)
+		return nil, errors.New("Don't know qemu for architecture %s", c.Architecture)
 	}
 
 	if q.qemusrc != "" {
 		q.qemutarget = path.Join(c.Chroot, q.qemusrc)
 	}
 
-	return q
+	return q, nil
 }
 
 func (q qemuHelper) Setup() error {

filesystem.go

@@ -4,7 +4,6 @@ import (
 	"fmt"
 	"io"
 	"io/ioutil"
-	"log"
 	"os"
 	"path"
 	"path/filepath"
@@ -71,18 +70,18 @@ func CopyTree(sourcetree, desttree string) error {
 		case 0:
 			err := CopyFile(p, target, info.Mode())
 			if err != nil {
-				log.Panicf("Failed to copy file %s: %v", p, err)
+				return fmt.Errorf("Failed to copy file %s: %v", p, err)
 			}
 		case os.ModeDir:
 			os.Mkdir(target, info.Mode())
 		case os.ModeSymlink:
 			link, err := os.Readlink(p)
 			if err != nil {
-				log.Panicf("Failed to read symlink %s: %v", suffix, err)
+				return fmt.Errorf("Failed to read symlink %s: %v", suffix, err)
 			}
 			os.Symlink(link, target)
 		default:
-			log.Panicf("Not handled /%s %v", suffix, info.Mode())
+			return fmt.Errorf("Not handled /%s %v", suffix, info.Mode())
 		}
 
 		return nil