Enum WhiteoutSpec 

pub enum WhiteoutSpec {
    Oci,
    Overlayfs,
    None,
}

RAFS filesystem overlay specifications.

When merging multiple RAFS filesystems into one, special rules are needed to white out files/directories in lower/parent filesystems. The whiteout specification defined by the OCI image specification and Linux Overlayfs are widely adopted, so both of them are supported by RAFS filesystem.

Overlayfs Whiteout

In order to support rm and rmdir without changing the lower filesystem, an overlay filesystem needs to record in the upper filesystem that files have been removed. This is done using whiteouts and opaque directories (non-directories are always opaque).

A whiteout is created as a character device with 0/0 device number. When a whiteout is found in the upper level of a merged directory, any matching name in the lower level is ignored, and the whiteout itself is also hidden.

A directory is made opaque by setting the xattr “trusted.overlay.opaque” to “y”. Where the upper filesystem contains an opaque directory, any directory in the lower filesystem with the same name is ignored.

OCI Image Whiteout

• A whiteout file is an empty file with a special filename that signifies a path should be deleted.
• A whiteout filename consists of the prefix .wh. plus the basename of the path to be deleted.
• As files prefixed with .wh. are special whiteout markers, it is not possible to create a filesystem which has a file or directory with a name beginning with .wh..
• Once a whiteout is applied, the whiteout itself MUST also be hidden.
• Whiteout files MUST only apply to resources in lower/parent layers.
• Files that are present in the same layer as a whiteout file can only be hidden by whiteout files in subsequent layers.
• In addition to expressing that a single entry should be removed from a lower layer, layers may remove all of the children using an opaque whiteout entry.
• An opaque whiteout entry is a file with the name .wh..wh..opq indicating that all siblings are hidden in the lower layer.

Variants

Oci

Overlay whiteout rules according to the OCI image specification.

https://github.com/opencontainers/image-spec/blob/master/layer.md#whiteouts

Overlayfs

Overlay whiteout rules according to the Linux Overlayfs specification.

“whiteouts and opaque directories” in https://www.kernel.org/doc/Documentation/filesystems/overlayfs.txt

None

No whiteout, keep all content from lower/parent filesystems.

Trait Implementations

impl Clone for WhiteoutSpec

fn clone(&self) -> WhiteoutSpec

Returns a duplicate of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl Default for WhiteoutSpec

fn default() -> Self

Returns the “default value” for a type.

impl Display for WhiteoutSpec

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

impl FromStr for WhiteoutSpec

type Err = Error

The associated error which can be returned from parsing.

fn from_str(s: &str) -> Result<Self>

Parses a string s to return a value of this type.

impl PartialEq for WhiteoutSpec

fn eq(&self, other: &WhiteoutSpec) -> bool

Tests for self and other values to be equal, and is used by ==.

fn ne(&self, other: &Rhs) -> bool

Tests for !=. The default implementation is almost always sufficient, and should not be overridden without very good reason.

impl Copy for WhiteoutSpec

impl StructuralPartialEq for WhiteoutSpec