iso: improve burn-in, export, and live boot

audit/internal/platform/export.go

@@ -11,8 +11,48 @@ import (
 
 var exportExecCommand = exec.Command
 
+func formatMountTargetError(target RemovableTarget, raw string, err error) error {
+	msg := strings.TrimSpace(raw)
+	fstype := strings.ToLower(strings.TrimSpace(target.FSType))
+	if fstype == "exfat" && strings.Contains(strings.ToLower(msg), "unknown filesystem type 'exfat'") {
+		return fmt.Errorf("mount %s: exFAT support is missing in this ISO build: %w", target.Device, err)
+	}
+	if msg == "" {
+		return err
+	}
+	return fmt.Errorf("%s: %w", msg, err)
+}
+
+func removableTargetReadOnly(fields map[string]string) bool {
+	if fields["RO"] == "1" {
+		return true
+	}
+	switch strings.ToLower(strings.TrimSpace(fields["FSTYPE"])) {
+	case "iso9660", "squashfs":
+		return true
+	default:
+		return false
+	}
+}
+
+func ensureWritableMountpoint(mountpoint string) error {
+	probe, err := os.CreateTemp(mountpoint, ".bee-write-test-*")
+	if err != nil {
+		return fmt.Errorf("target filesystem is not writable: %w", err)
+	}
+	name := probe.Name()
+	if closeErr := probe.Close(); closeErr != nil {
+		_ = os.Remove(name)
+		return closeErr
+	}
+	if err := os.Remove(name); err != nil {
+		return err
+	}
+	return nil
+}
+
 func (s *System) ListRemovableTargets() ([]RemovableTarget, error) {
-	raw, err := exportExecCommand("lsblk", "-P", "-o", "NAME,TYPE,PKNAME,RM,FSTYPE,MOUNTPOINT,SIZE,LABEL,MODEL").Output()
+	raw, err := exportExecCommand("lsblk", "-P", "-o", "NAME,TYPE,PKNAME,RM,RO,FSTYPE,MOUNTPOINT,SIZE,LABEL,MODEL").Output()
 	if err != nil {
 		return nil, err
 	}
@@ -36,7 +76,7 @@ func (s *System) ListRemovableTargets() ([]RemovableTarget, error) {
 				}
 			}
 		}
-		if !removable || fields["FSTYPE"] == "" {
+		if !removable || fields["FSTYPE"] == "" || removableTargetReadOnly(fields) {
 			continue
 		}
 
@@ -72,7 +112,7 @@ func (s *System) ExportFileToTarget(src string, target RemovableTarget) (dst str
 		}
 		if raw, err := exportExecCommand("mount", target.Device, mountpoint).CombinedOutput(); err != nil {
 			_ = os.Remove(mountpoint)
-			return string(raw), err
+			return "", formatMountTargetError(target, string(raw), err)
 		}
 		mountedHere = true
 		mounted = true
@@ -95,6 +135,10 @@ func (s *System) ExportFileToTarget(src string, target RemovableTarget) (dst str
 		}
 	}()
 
+	if err := ensureWritableMountpoint(mountpoint); err != nil {
+		return "", err
+	}
+
 	filename := filepath.Base(src)
 	dst = filepath.Join(mountpoint, filename)
 	data, err := os.ReadFile(src)