btrfs_diskformat/core/
root_item.rs

1use {
2    crate::{InodeItem, Key, Time, UuidBytes},
3    byteorder::LE,
4    static_assertions::const_assert_eq,
5    zerocopy::{AsBytes, FromBytes, Unaligned, U32, U64},
6};
7
8/// Defines the location and parameters of the root of a b-tree.
9#[derive(Copy, Clone, Debug, AsBytes, FromBytes, Unaligned)]
10#[repr(C, packed)]
11pub struct RootItem {
12    pub inode: InodeItem,
13
14    pub generation: U64<LE>,
15
16    pub root_dirid: U64<LE>,
17
18    pub bytenr: U64<LE>,
19
20    /// Currently unused. Always 0.
21    pub byte_limit: U64<LE>,
22
23    /// Currently unused.
24    pub bytes_used: U64<LE>,
25
26    /// The transaction ID of the last transaction that created a snapshot of this root.
27    pub last_snapshot: U64<LE>,
28
29    pub flags: U64<LE>,
30
31    /// Only 0 or 1. Historically contained a reference count.
32    pub refs: U32<LE>,
33
34    /// Contains the key of the last dropped item during subvolume removal or relocation.
35    ///
36    /// Value will be zeroed out otherwise.
37    pub drop_progress: Key,
38
39    /// The tree level of the node referenced in [drop_progress](RootItem::drop_progress).
40    pub drop_level: u8,
41
42    /// The height of this root's tree.
43    pub level: u8,
44
45    /// Value to help determine whether this root has been modified by an older btrfs
46    /// implementation.
47    ///
48    /// If the value is equal to [generation], the fields below are valid. Otherwise, this indicates
49    /// the fields are invalid but recoverable.
50    ///
51    /// [generation]: RootItem::generation
52    pub generation_v2: U64<LE>,
53
54    /// The subvolume's UUID.
55    pub uuid: UuidBytes,
56
57    /// The parent's subvolume UUID.
58    ///
59    /// This is used during send/receive.
60    pub parent_uuid: UuidBytes,
61
62    /// The received UUID.
63    ///
64    /// This is used during send/receive.
65    pub received_uuid: UuidBytes,
66
67    /// The transaction ID of the last transaction that modified the tree.
68    ///
69    /// Note: some operations like internal caches or relocation will not update this value.
70    pub ctransid: U64<LE>,
71
72    /// The transaction ID of the transaction that created the tree.
73    pub otransid: U64<LE>,
74
75    /// The transaction ID for the transaction that sent this subvolume.
76    ///
77    /// This value is non-zero for a received subvolume.
78    pub stransid: U64<LE>,
79
80    /// The transaction ID for the transaction that received this subvolume.
81    ///
82    /// This value is non-zero for a received subvolume.
83    pub rtransid: U64<LE>,
84
85    /// The timestamp of the [`ctransid`](RootItem::ctransid).
86    pub ctime: Time,
87
88    /// The timestamp of the [`otransid`](RootItem::otransid).
89    pub otime: Time,
90
91    /// The timestamp of the [`stransid`](RootItem::stransid).
92    pub stime: Time,
93
94    /// The timestamp of the [`rtransid`](RootItem::rtransid).
95    pub rtime: Time,
96
97    /// Currently unused. Reserved for future use.
98    pub _unused: [u64; 8],
99}
100const_assert_eq!(core::mem::size_of::<RootItem>(), 439);
btrfs_diskformat/core/root_item.rs

btrfs_diskformat/core/
root_item.rs
