Enum PreallocateMode

#[non_exhaustive]
pub enum PreallocateMode {
    None,
    Zero,
    FormatAllocate,
    FullAllocate,
    WriteData,
}

Format layer preallocation modes.

When resizing or create an image, this mode determines whether and how the new data range is to be preallocated.

Variants (Non-exhaustive)

Non-exhaustive enums could have additional variants added in future. Therefore, when matching against variants of non-exhaustive enums, an extra wildcard arm must be added to account for any future variants.

None

No preallocation.

Reading the new range may return random data.

Zero

Ensure range reads as zeroes.

Does not necessarily allocate data, but has to ensure the new range will read back as zeroes (e.g. a backing file’s contents must not show through).

FormatAllocate

Metadata preallocation.

Do not write data, but ensure all blocks are mapped as data. For images without a backing file, that data must read as zeroes. For images with a backing file, that data must be the same as the backing file’s contents, and zeroes beyond the backing file EOF.

FullAllocate

Metadata and extent preallocation.

Same as FormatAllocate, but also allocate all blocks on the underlying storage.

WriteData

Full data preallocation.

Write data to the whole range. For images without a backing file, that data must read as zeroes. For images with a backing file, that data must be the same as the backing file’s contents, and zeroes beyond the backing file EOF.

Trait Implementations

impl Clone for PreallocateMode

fn clone(&self) -> PreallocateMode

Returns a duplicate of the value.

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

Performs copy-assignment from source.

impl Debug for PreallocateMode

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

Formats the value using the given formatter.

impl PartialEq for PreallocateMode

fn eq(&self, other: &PreallocateMode) -> 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 PreallocateMode

impl Eq for PreallocateMode

impl StructuralPartialEq for PreallocateMode