Struct SuperBlock

#[repr(C, packed(1))]
pub struct SuperBlock {

    pub csum: [u8; 32],
    pub fsid: [u8; 16],
    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: DevItem,
    pub label: [u8; 256],
    pub cache_generation: U64,
    pub uuid_tree_generation: U64,
    pub _reserved: [U64; 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

The physical address of this block.

flags: U64

Flags

magic: U64

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

generation: U64

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

root: U64

The logical address of the root tree’s root.

chunk_root: U64

The logical address of the chunk tree’s root.

log_root: U64

The logical address of the log tree’s root.

log_root_transid: U64

FIXME: find out what this is!

total_bytes: U64

FIXME: document this!

bytes_used: U64

root_dir_objectid: U64

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

num_devices: U64

The number of devices the current filesystem spans.

sectorsize: U32

The size of a sector.

nodesize: U32

leafsize: U32

This is currently unused.

stripesize: U32

sys_chunk_array_size: U32

The size of sys_chunk_array found in the superblock.

chunk_root_generation: U64

compat_flags: U64

compat_ro_flags: U64

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

incompat_flags: U64

Only implementations that support these flags can use the filesystem.

csum_type: ChecksumType

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

uuid_tree_generation: U64

_reserved: [U64; 30]

Reserved for extensibility.

sys_chunk_array: [u8; 2048]

super_roots: [RootBackup; 4]

_unused1: [u8; 565]

Trait Implementations

impl Clone for SuperBlock

fn clone(&self) -> SuperBlock

Returns a copy of the value.

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

Performs copy-assignment from source.

impl KnownLayout for SuperBlock

where [u8; 565]: KnownLayout,

type PointerMetadata = <[u8; 565] as KnownLayout>::PointerMetadata

The type of metadata stored in a pointer to Self.

impl TryFromBytes for SuperBlock

where [u8; 32]: TryFromBytes, [u8; 16]: TryFromBytes, U64: TryFromBytes, U32: TryFromBytes, ChecksumType: TryFromBytes, u8: TryFromBytes, DevItem: TryFromBytes, [u8; 256]: TryFromBytes, [U64; 30]: TryFromBytes, [u8; 2048]: TryFromBytes, [RootBackup; 4]: TryFromBytes, [u8; 565]: TryFromBytes,

fn try_mut_from_bytes( bytes: &mut [u8], ) -> Result<&mut Self, ConvertError<AlignmentError<&mut [u8], Self>, SizeError<&mut [u8], Self>, ValidityError<&mut [u8], Self>>>

where Self: KnownLayout + IntoBytes,

Attempts to interpret the given source as a &mut Self without copying.

fn try_mut_from_prefix( source: &mut [u8], ) -> Result<(&mut Self, &mut [u8]), ConvertError<AlignmentError<&mut [u8], Self>, SizeError<&mut [u8], Self>, ValidityError<&mut [u8], Self>>>

where Self: KnownLayout + IntoBytes,

Attempts to interpret the prefix of the given source as a &mut Self.

fn try_mut_from_suffix( source: &mut [u8], ) -> Result<(&mut [u8], &mut Self), ConvertError<AlignmentError<&mut [u8], Self>, SizeError<&mut [u8], Self>, ValidityError<&mut [u8], Self>>>

where Self: KnownLayout + IntoBytes,

Attempts to interpret the suffix of the given source as a &mut Self.

fn try_mut_from_bytes_with_elems( source: &mut [u8], count: usize, ) -> Result<&mut Self, ConvertError<AlignmentError<&mut [u8], Self>, SizeError<&mut [u8], Self>, ValidityError<&mut [u8], Self>>>

where Self: KnownLayout<PointerMetadata = usize> + IntoBytes,

Attempts to interpret the given source as a &mut Self with a DST length equal to count.

fn try_mut_from_prefix_with_elems( source: &mut [u8], count: usize, ) -> Result<(&mut Self, &mut [u8]), ConvertError<AlignmentError<&mut [u8], Self>, SizeError<&mut [u8], Self>, ValidityError<&mut [u8], Self>>>

where Self: KnownLayout<PointerMetadata = usize> + IntoBytes,

Attempts to interpret the prefix of the given source as a &mut Self with a DST length equal to count.

fn try_mut_from_suffix_with_elems( source: &mut [u8], count: usize, ) -> Result<(&mut [u8], &mut Self), ConvertError<AlignmentError<&mut [u8], Self>, SizeError<&mut [u8], Self>, ValidityError<&mut [u8], Self>>>

where Self: KnownLayout<PointerMetadata = usize> + IntoBytes,

Attempts to interpret the suffix of the given source as a &mut Self with a DST length equal to count.

fn try_read_from_bytes( source: &[u8], ) -> Result<Self, ConvertError<Infallible, SizeError<&[u8], Self>, ValidityError<&[u8], Self>>>

where Self: Sized,

Attempts to read the given source as a Self.

fn try_read_from_prefix( source: &[u8], ) -> Result<(Self, &[u8]), ConvertError<Infallible, SizeError<&[u8], Self>, ValidityError<&[u8], Self>>>

where Self: Sized,

Attempts to read a Self from the prefix of the given source.

fn try_read_from_suffix( source: &[u8], ) -> Result<(&[u8], Self), ConvertError<Infallible, SizeError<&[u8], Self>, ValidityError<&[u8], Self>>>

where Self: Sized,

Attempts to read a Self from the suffix of the given source.

impl Copy for SuperBlock

impl IntoBytes for SuperBlock

where [u8; 32]: IntoBytes, [u8; 16]: IntoBytes, U64: IntoBytes, U32: IntoBytes, ChecksumType: IntoBytes, u8: IntoBytes, DevItem: IntoBytes, [u8; 256]: IntoBytes, [U64; 30]: IntoBytes, [u8; 2048]: IntoBytes, [RootBackup; 4]: IntoBytes, [u8; 565]: IntoBytes,

impl Unaligned for SuperBlock