Struct qcow::QcowHeader

pub struct QcowHeader {
    pub version: u32,
    pub backing_file: Option<String>,
    pub cluster_bits: u32,
    pub size: u64,
    pub crypt_method: EncryptionMethod,
    pub l1_size: u32,
    pub l1_table_offset: u64,
    pub refcount_table_offset: u64,
    pub refcount_table_clusters: u32,
    pub v3_header: Option<Version3Header>,
    pub extensions: Vec<HeaderExt>,
    // some fields omitted
}

Top-level header of Qcow format

Fields

version: u32

Version of the QCOW format. Only version 2 or 3 is supported, future formats will throw a parsing error upon being read.

backing_file: Option<String>

Backing file represented as a string, if any.

cluster_bits: u32

Number of bits that are used for addressing an offset within a cluster (1 << cluster_bits is the cluster size). Must not be less than 9 (i.e. 512 byte clusters).

Note: qemu as of today has an implementation limit of 2 MB as the maximum cluster size and won’t be able to open images with larger cluster sizes.

Note: if the image has Extended L2 Entries then cluster_bits must be at least 14 (i.e. 16384 byte clusters).

size: u64

Virtual disk size in bytes.

Note: qemu has an implementation limit of 32 MB as the maximum L1 table size. With a 2 MB cluster size, it is unable to populate a virtual cluster beyond 2 EB (61 bits); with a 512 byte cluster size, it is unable to populate a virtual size larger than 128 GB (37 bits). Meanwhile, L1/L2 table layouts limit an image to no more than 64 PB (56 bits) of populated clusters, and an image may hit other limits first (such as a file system’s maximum size).

crypt_method: EncryptionMethod

Encryption method to use for contents

l1_size: u32

Number of entries in the active L1 table

l1_table_offset: u64

Offset into the image file at which the active L1 table starts. Must be aligned to a cluster boundary.

refcount_table_offset: u64

Offset into the image file at which the refcount table starts. Must be aligned to a cluster boundary.

refcount_table_clusters: u32

Number of clusters that the refcount table occupies

v3_header: Option<Version3Header>

Part of header only present in qcow version 3, otherwise set to None

extensions: Vec<HeaderExt>

Extentions to the header format

Implementations

impl QcowHeader

pub fn cluster_size(&self) -> u64

Get the size of a cluster in bytes from the qcow

Trait Implementations

impl BinRead for QcowHeader

type Args = ()

The type of arguments needed to be supplied in order to read this type, usually a tuple.

fn read_options<R: Read + Seek>(
    __binread_generated_var_reader: &mut R,
    __binread_generated_var_options: &ReadOptions,
    __binread_generated_var_arguments: Self::Args
) -> BinResult<Self>

Read the type from the reader

fn read<R>(reader: &mut R) -> Result<Self, Error> where
    R: Read + Seek, 

Read the type from the reader while assuming no arguments have been passed

fn read_args<R>(reader: &mut R, args: Self::Args) -> Result<Self, Error> where
    R: Read + Seek, 

Read the type from the reader using the specified arguments

fn after_parse<R>(
    &mut self,
    &mut R,
    &ReadOptions,
    Self::Args
) -> Result<(), Error> where
    R: Read + Seek, 

fn args_default() -> Option<Self::Args>

The default arguments to be used when using the read shortcut method. Override this for any type that optionally requries arguments

impl Debug for QcowHeader

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

Formats the value using the given formatter.