Struct Superblock 

pub struct Superblock {

    pub csum: [u8; 32],
    pub fsid: Uuid,
    pub bytenr: u64,
    pub flags: u64,
    pub magic: u64,
    pub generation: u64,
    pub root: u64,
    pub chunk_root: u64,
    pub log_root: u64,
    pub log_root_transid: u64,
    pub total_bytes: u64,
    pub bytes_used: u64,
    pub root_dir_objectid: u64,
    pub num_devices: u64,
    pub sectorsize: u32,
    pub nodesize: u32,
    pub leafsize: u32,
    pub stripesize: u32,
    pub sys_chunk_array_size: u32,
    pub chunk_root_generation: u64,
    pub compat_flags: u64,
    pub compat_ro_flags: u64,
    pub incompat_flags: u64,
    pub csum_type: ChecksumType,
    pub root_level: u8,
    pub chunk_root_level: u8,
    pub log_root_level: u8,
    pub dev_item: DeviceItem,
    pub label: String,
    pub cache_generation: u64,
    pub uuid_tree_generation: u64,
    pub metadata_uuid: Uuid,
    pub nr_global_roots: u64,
    pub backup_roots: [BackupRoot; 4],
    pub sys_chunk_array: [u8; 2048],
}

Parsed btrfs superblock.

The superblock is the entry point for reading a btrfs filesystem. It lives at a fixed offset on each device (see super_mirror_offset) and contains the root pointers, feature flags, and embedded system chunk array needed to bootstrap access to all other on-disk structures.

Fields

csum: [u8; 32]

Checksum of everything past this field (bytes 32..4096).

fsid: Uuid

Filesystem UUID. Shared by all devices in a multi-device filesystem.

bytenr: u64

Physical byte offset where this superblock is stored on disk.

flags: u64

Superblock flags (BTRFS_SUPER_FLAG_*).

magic: u64

Magic number (_BHRfS_M). See Superblock::magic_is_valid.

generation: u64

Transaction generation of this superblock write.

root: u64

Logical bytenr of the root tree root block.

chunk_root: u64

Logical bytenr of the chunk tree root block.

log_root: u64

Logical bytenr of the log tree root block (0 if no log tree).

log_root_transid: u64

Transaction ID of the log tree root.

total_bytes: u64

Total usable bytes across all devices.

bytes_used: u64

Total bytes used by data and metadata.

root_dir_objectid: u64

Objectid of the root directory (always 6).

num_devices: u64

Number of devices in this filesystem.

sectorsize: u32

Minimum I/O alignment (typically 4096).

nodesize: u32

Size of tree blocks in bytes (typically 16384).

leafsize: u32

Legacy field, equal to nodesize in modern filesystems.

stripesize: u32

Stripe size for RAID (typically 65536).

sys_chunk_array_size: u32

Number of valid bytes in the sys_chunk_array.

chunk_root_generation: u64

Generation of the chunk tree root.

compat_flags: u64

Compatible feature flags.

compat_ro_flags: u64

Compatible read-only feature flags.

incompat_flags: u64

Incompatible feature flags (e.g. MIXED_GROUPS, SKINNY_METADATA).

csum_type: ChecksumType

Checksum algorithm for this filesystem.

root_level: u8

B-tree level of the root tree root.

chunk_root_level: u8

B-tree level of the chunk tree root.

log_root_level: u8

B-tree level of the log tree root.

dev_item: DeviceItem

Embedded device item describing this device.

label: String

Filesystem label (up to 255 bytes, NUL-terminated on disk).

cache_generation: u64

Generation when the free space cache was written (v1 cache).

uuid_tree_generation: u64

Generation when the UUID tree was last updated.

metadata_uuid: Uuid

Metadata UUID (differs from fsid when METADATA_UUID incompat flag is set).

nr_global_roots: u64

Number of global root entries (extent-tree-v2, not yet used).

backup_roots: [BackupRoot; 4]

Four rotating backup copies of critical tree root pointers.

sys_chunk_array: [u8; 2048]

Embedded chunk tree entries for bootstrapping the chunk cache.

Implementations

impl Superblock

pub fn magic_is_valid(&self) -> bool

Whether the magic bytes match BTRFS_MAGIC.

pub fn has_metadata_uuid(&self) -> bool

Whether the METADATA_UUID incompat flag is set.

pub fn to_bytes(&self) -> [u8; 4096]

Serialize the superblock to a 4096-byte buffer.

The checksum field is written as-is from self.csum; call csum_superblock on the result to recompute it.

Trait Implementations

impl Clone for Superblock

fn clone(&self) -> Superblock

Returns a duplicate of the value.

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

Performs copy-assignment from source.

impl Debug for Superblock

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

Formats the value using the given formatter.