btrfs_diskformat/core/
super_block.rs

1use crate::{
2    DevItem, RootBackup,
3    constants::{CSUM_SIZE, FSID_SIZE, LABEL_SIZE, MAX_SYSTEM_CHUNK_ARRAY_SIZE, NUM_BACKUP_ROOTS},
4};
5use num_enum::{IntoPrimitive, TryFromPrimitive};
6use static_assertions::const_assert_eq;
7use strum::EnumIter;
8use zerocopy::little_endian::{U32 as U32LE, U64 as U64LE};
9use zerocopy_derive::*;
10
11/// The layout of the superblock. A valid superblock must exist for most btrfs implementations to
12/// mount the filesystem.
13///
14/// The primary superblock is located at [`PRIMARY_SUPERBLOCK_ADDR`].
15///
16/// There are additional copies of the superblock located at [`SUPERBLOCK_ADDRS`], if those addresses
17/// are valid, respectively.
18///
19///
20/// [`PRIMARY_SUPERBLOCK_ADDR`]: crate::constants::PRIMARY_SUPERBLOCK_ADDR
21/// [`SUPERBLOCK_ADDRS`]: crate::constants::SUPERBLOCK_ADDRS
22///
23/// # Resources
24///
25///  * <https://btrfs.wiki.kernel.org/index.php/Data_Structures#btrfs_super_block>
26///  * <https://btrfs.wiki.kernel.org/index.php/On-disk_Format#Superblock>
27#[derive(Copy, Clone, IntoBytes, TryFromBytes, Unaligned, KnownLayout)]
28#[repr(C, packed)]
29pub struct SuperBlock {
30    /// Checksum of everything past this field.
31    pub csum: [u8; CSUM_SIZE],
32
33    /// Filesystem UUID.
34    pub fsid: [u8; FSID_SIZE],
35
36    /// The physical address of this block.
37    pub bytenr: U64LE,
38
39    /// Flags
40    pub flags: U64LE,
41
42    /// The magic must be equal to `"_BHRfS_M"` in ASCII.
43    pub magic: U64LE,
44
45    /// The generation of the superblock. In SSD mode, not all superblocks may be updated, so the
46    /// latest generation superblock should be used.
47    pub generation: U64LE,
48
49    /// The logical address of the root tree's root.
50    pub root: U64LE,
51
52    /// The logical address of the chunk tree's root.
53    pub chunk_root: U64LE,
54
55    /// The logical address of the log tree's root.
56    pub log_root: U64LE,
57
58    /// FIXME: find out what this is!
59    pub log_root_transid: U64LE,
60
61    /// FIXME: document this!
62    pub total_bytes: U64LE,
63
64    pub bytes_used: U64LE,
65
66    /// The root directory's object ID, which is typically 6.
67    pub root_dir_objectid: U64LE,
68
69    /// The number of devices the current filesystem spans.
70    pub num_devices: U64LE,
71
72    /// The size of a sector.
73    pub sectorsize: U32LE,
74
75    pub nodesize: U32LE,
76
77    /// This is currently unused.
78    pub leafsize: U32LE,
79
80    pub stripesize: U32LE,
81
82    /// The size of [`sys_chunk_array`] found in the superblock.
83    ///
84    /// [`sys_chunk_array`]: SuperBlock::sys_chunk_array
85    pub sys_chunk_array_size: U32LE,
86
87    pub chunk_root_generation: U64LE,
88
89    pub compat_flags: U64LE,
90
91    /// Only implementations that support these flags can write to the filesystem.
92    pub compat_ro_flags: U64LE,
93
94    /// Only implementations that support these flags can use the filesystem.
95    pub incompat_flags: U64LE,
96
97    /// The checksum type.
98    ///
99    /// This should correspond with a value from [`ChecksumType`].
100    ///
101    /// [`ChecksumType`]: crate::ChecksumType
102    pub csum_type: ChecksumType,
103
104    pub root_level: u8,
105
106    pub chunk_root_level: u8,
107
108    pub log_root_level: u8,
109
110    pub dev_item: DevItem,
111
112    /// The label represented as a null-terminated UTF-8 string. May not contain `'/'` or `'\\'`.
113    pub label: [u8; LABEL_SIZE],
114
115    pub cache_generation: U64LE,
116
117    pub uuid_tree_generation: U64LE,
118
119    /// Reserved for extensibility.
120    pub _reserved: [U64LE; 30],
121
122    pub sys_chunk_array: [u8; MAX_SYSTEM_CHUNK_ARRAY_SIZE],
123
124    pub super_roots: [RootBackup; NUM_BACKUP_ROOTS],
125
126    pub _unused1: [u8; 565],
127}
128const_assert_eq!(core::mem::size_of::<SuperBlock>(), 4096);
129
130/// The hashing algorithm used for checksumming.
131#[derive(
132    Copy,
133    Clone,
134    Debug,
135    Hash,
136    PartialEq,
137    EnumIter,
138    IntoPrimitive,
139    TryFromPrimitive,
140    TryFromBytes,
141    IntoBytes,
142    KnownLayout,
143)]
144#[repr(u16)]
145pub enum ChecksumType {
146    CRC32C = 0u16.to_le(),
147    XXHASH64 = 1u16.to_le(),
148    SHA256 = 2u16.to_le(),
149    BLAKE2b = 3u16.to_le(),
150}
151const_assert_eq!(core::mem::size_of::<ChecksumType>(), 2);
btrfs_diskformat/core/super_block.rs

btrfs_diskformat/core/
super_block.rs
