Return typed error when Mount Fails

Mount can fail for a variety of reasons and caller might want to know
why mount failed. Using untyped string based error does not provide
enough granularity to make that verification.

mount.go

@@ -20,6 +20,7 @@ limitations under the License.
 package mount
 
 import (
+	"fmt"
 	"os"
 	"path/filepath"
 	"strings"
@@ -76,6 +77,36 @@ type MountPoint struct {
 	Pass   int
 }
 
+type MountErrorType string
+
+const (
+	FilesystemMismatch  MountErrorType = "FilesystemMismatch"
+	HasFilesystemErrors MountErrorType = "HasFilesystemErrors"
+	UnformattedReadOnly MountErrorType = "UnformattedReadOnly"
+	FormatFailed        MountErrorType = "FormatFailed"
+)
+
+type MountError struct {
+	Type    MountErrorType
+	Message string
+}
+
+func (mountError *MountError) String() string {
+	return mountError.Message
+}
+
+func (mountError *MountError) Error() string {
+	return mountError.Message
+}
+
+func NewMountError(mountErrorValue MountErrorType, format string, args ...interface{}) error {
+	mountError := &MountError{
+		Type:    mountErrorValue,
+		Message: fmt.Sprintf(format, args...),
+	}
+	return mountError
+}
+
 // SafeFormatAndMount probes a device to see if it is formatted.
 // Namely it checks to see if a file system is present. If so it
 // mounts it otherwise the device is formatted first then mounted.

mount_linux.go

@@ -267,6 +267,7 @@ func (mounter *SafeFormatAndMount) formatAndMount(source string, target string,
 	}
 
 	options = append(options, "defaults")
+	var mountErrorValue MountErrorType
 
 	if !readOnly {
 		// Run fsck on the disk to fix repairable issues, only do this for volumes requested as rw.
@@ -281,7 +282,7 @@ func (mounter *SafeFormatAndMount) formatAndMount(source string, target string,
 			case isExitError && ee.ExitStatus() == fsckErrorsCorrected:
 				klog.Infof("Device %s has errors which were corrected by fsck.", source)
 			case isExitError && ee.ExitStatus() == fsckErrorsUncorrected:
-				return fmt.Errorf("'fsck' found errors on device %s but could not correct them: %s", source, string(out))
+				return NewMountError(HasFilesystemErrors, "'fsck' found errors on device %s but could not correct them: %s", source, string(out))
 			case isExitError && ee.ExitStatus() > fsckErrorsUncorrected:
 				klog.Infof("`fsck` error %s", string(out))
 			}
@@ -302,7 +303,7 @@ func (mounter *SafeFormatAndMount) formatAndMount(source string, target string,
 	if existingFormat == "" {
 		// Do not attempt to format the disk if mounting as readonly, return an error to reflect this.
 		if readOnly {
-			return fmt.Errorf("cannot mount unformatted disk %s as we are manipulating it in read-only mode", source)
+			return NewMountError(UnformattedReadOnly, "cannot mount unformatted disk %s as we are manipulating it in read-only mode", source)
 		}
 
 		// Disk is unformatted so format it.
@@ -319,19 +320,20 @@ func (mounter *SafeFormatAndMount) formatAndMount(source string, target string,
 		_, err := mounter.Exec.Command("mkfs."+fstype, args...).CombinedOutput()
 		if err != nil {
 			klog.Errorf("format of disk %q failed: type:(%q) target:(%q) options:(%q)error:(%v)", source, fstype, target, options, err)
-			return err
+			return NewMountError(FormatFailed, err.Error())
 		}
 
 		klog.Infof("Disk successfully formatted (mkfs): %s - %s %s", fstype, source, target)
 	} else if fstype != existingFormat {
 		// Verify that the disk is formatted with filesystem type we are expecting
+		mountErrorValue = FilesystemMismatch
 		klog.Warningf("Configured to mount disk %s as %s but current format is %s, things might break", source, existingFormat, fstype)
 	}
 
 	// Mount the disk
 	klog.V(4).Infof("Attempting to mount disk %s in %s format at %s", source, fstype, target)
 	if err := mounter.Interface.Mount(source, target, fstype, options); err != nil {
-		return err
+		return NewMountError(mountErrorValue, err.Error())
 	}
 
 	return nil