Struct btrfs_diskformat::SuperBlock

#[repr(C, packed)]pub struct SuperBlock {
    pub csum: [u8; 32],
    pub fsid: [u8; 16],
    pub bytenr: U64<LE>,
    pub flags: U64<LE>,
    pub magic: U64<LE>,
    pub generation: U64<LE>,
    pub root: U64<LE>,
    pub chunk_root: U64<LE>,
    pub log_root: U64<LE>,
    pub log_root_transid: U64<LE>,
    pub total_bytes: U64<LE>,
    pub bytes_used: U64<LE>,
    pub root_dir_objectid: U64<LE>,
    pub num_devices: U64<LE>,
    pub sectorsize: U32<LE>,
    pub nodesize: U32<LE>,
    pub leafsize: U32<LE>,
    pub stripesize: U32<LE>,
    pub sys_chunk_array_size: U32<LE>,
    pub chunk_root_generation: U64<LE>,
    pub compat_flags: U64<LE>,
    pub compat_ro_flags: U64<LE>,
    pub incompat_flags: U64<LE>,
    pub csum_type: U16<LE>,
    pub root_level: u8,
    pub chunk_root_level: u8,
    pub log_root_level: u8,
    pub dev_item: DevItem,
    pub label: [u8; 256],
    pub cache_generation: U64<LE>,
    pub uuid_tree_generation: U64<LE>,
    pub _reserved: [U64<LE>; 30],
    pub sys_chunk_array: [u8; 2048],
    pub super_roots: [RootBackup; 4],
    pub _unused1: [u8; 565],
}

The layout of the superblock. A valid superblock must exist for most btrfs implementations to mount the filesystem.

The primary superblock is located at PRIMARY_SUPERBLOCK_ADDR.

There are additional copies of the superblock located at SUPERBLOCK_ADDRS, if those addresses are valid, respectively.

Resources

• https://btrfs.wiki.kernel.org/index.php/Data_Structures#btrfs_super_block
• https://btrfs.wiki.kernel.org/index.php/On-disk_Format#Superblock

Fields

csum: [u8; 32]

Checksum of everything past this field.

fsid: [u8; 16]

Filesystem UUID.

bytenr: U64<LE>

The physical address of this block.

flags: U64<LE>

Flags

magic: U64<LE>

The magic must be equal to "_BHRfS_M" in ASCII.

generation: U64<LE>

The generation of the superblock. In SSD mode, not all superblocks may be updated, so the latest generation superblock should be used.

root: U64<LE>

The logical address of the root tree’s root.

chunk_root: U64<LE>

The logical address of the chunk tree’s root.

log_root: U64<LE>

The logical address of the log tree’s root.

log_root_transid: U64<LE>

FIXME: find out what this is!

total_bytes: U64<LE>

FIXME: document this!

bytes_used: U64<LE>

root_dir_objectid: U64<LE>

The root directory’s object ID, which is typically 6.

num_devices: U64<LE>

The number of devices the current filesystem spans.

sectorsize: U32<LE>

The size of a sector.

nodesize: U32<LE>

leafsize: U32<LE>

This is currently unused.

stripesize: U32<LE>

sys_chunk_array_size: U32<LE>

The size of sys_chunk_array found in the superblock.

chunk_root_generation: U64<LE>

compat_flags: U64<LE>

compat_ro_flags: U64<LE>

Only implementations that support these flags can write to the filesystem.

incompat_flags: U64<LE>

Only implementations that support these flags can use the filesystem.

csum_type: U16<LE>

The checksum type.

This should correspond with a value from ChecksumType.

root_level: u8

chunk_root_level: u8

log_root_level: u8

dev_item: DevItem

label: [u8; 256]

The label represented as a null-terminated UTF-8 string. May not contain '/' or '\\'.

cache_generation: U64<LE>

uuid_tree_generation: U64<LE>

_reserved: [U64<LE>; 30]

Reserved for extensibility.

sys_chunk_array: [u8; 2048]

super_roots: [RootBackup; 4]

_unused1: [u8; 565]

Trait Implementations

impl AsBytes for SuperBlock

fn only_derive_is_allowed_to_implement_this_trait() where
    Self: Sized, 

pub fn as_bytes(&self) -> &[u8]

Get the bytes of this value.

pub fn as_bytes_mut(&mut self) -> &mut [u8] where
    Self: FromBytes, 

Get the bytes of this value mutably.

impl Clone for SuperBlock

fn clone(&self) -> SuperBlock

Returns a copy of the value.

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

Performs copy-assignment from source.

impl Copy for SuperBlock

impl FromBytes for SuperBlock

fn only_derive_is_allowed_to_implement_this_trait() where
    Self: Sized, 

impl Unaligned for SuperBlock

fn only_derive_is_allowed_to_implement_this_trait() where
    Self: Sized,