Struct V2Header

struct V2Header {

    magic: u32,
    version: u32,
    backing_file_offset: u64,
    backing_file_size: u32,
    cluster_bits: u32,
    size: AtomicU64,
    crypt_method: u32,
    l1_size: AtomicU32,
    l1_table_offset: AtomicU64,
    refcount_table_offset: AtomicU64,
    refcount_table_clusters: AtomicU32,
    nb_snapshots: u32,
    snapshots_offset: u64,
}

Qcow2 v2 header.

Fields

magic: u32

Qcow magic string (“QFI\xfb”).

version: u32

Version number (valid values are 2 and 3).

backing_file_offset: u64

Offset into the image file at which the backing file name is stored (NB: The string is not null terminated). 0 if the image doesn’t have a backing file.

Note: backing files are incompatible with raw external data files (auto-clear feature bit 1).

backing_file_size: u32

Length of the backing file name in bytes. Must not be longer than 1023 bytes. Undefined if the image doesn’t have a backing file.

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: AtomicU64

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: u32

Encryption method:

0. no encryption
1. AES encryption
2. LUKS encryption

l1_size: AtomicU32

Number of entries in the active L1 table.

l1_table_offset: AtomicU64

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

refcount_table_offset: AtomicU64

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

refcount_table_clusters: AtomicU32

Number of clusters that the refcount table occupies.

nb_snapshots: u32

Number of snapshots contained in the image.

snapshots_offset: u64

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

Implementations

impl V2Header

const RAW_SIZE: usize = 72usize

Raw v2 header length.

Trait Implementations

impl<'de> Deserialize<'de> for V2Header

fn deserialize<__D>(__deserializer: __D) -> Result<Self, __D::Error>

where __D: Deserializer<'de>,

Deserialize this value from the given Serde deserializer.

impl Serialize for V2Header

fn serialize<__S>(&self, __serializer: __S) -> Result<__S::Ok, __S::Error>

where __S: Serializer,

Serialize this value into the given Serde serializer.