rsext4 0.3.7

A lightweight ext4 file system.
Documentation 
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159

//! Inode-local metadata mutation helpers.

use super::{
    Ext4DtimeUpdate, Ext4InodeMetadataUpdate, Ext4ModeUpdate,
    time::{get_now, resolve_time_spec},
};
use crate::{
    blockdev::{BlockDevice, Jbd2Dev},
    disknode::{Ext4Inode, Ext4Timestamp},
    error::{Ext4Error, Ext4Result},
    ext4::Ext4FileSystem,
};

impl Ext4FileSystem {
    pub(crate) fn inode_disk_size(&self) -> u16 {
        match self.superblock.s_inode_size {
            0 => Ext4Inode::LARGE_INODE_SIZE,
            size => size,
        }
    }

    pub(crate) fn default_inode_extra_isize(&self) -> u16 {
        let max_extra = Ext4Inode::max_extra_isize(self.inode_disk_size());
        let mut extra = core::cmp::min(self.superblock.s_want_extra_isize, max_extra);
        extra &= !3;
        extra
    }

    fn try_expand_extra_isize_for_field(&self, inode: &mut Ext4Inode, field_end: u16) -> bool {
        let inode_size = self.inode_disk_size();
        let max_extra = Ext4Inode::max_extra_isize(inode_size);
        let required = Ext4Inode::required_extra_isize(field_end);
        if required > max_extra {
            return false;
        }
        if inode.i_extra_isize >= required {
            return true;
        }

        let mut target = core::cmp::max(required, self.default_inode_extra_isize());
        target &= !3;
        if target > max_extra {
            return false;
        }

        inode.i_extra_isize = target;
        true
    }

    pub(crate) fn ensure_extra_isize_for_field(
        &self,
        inode: &mut Ext4Inode,
        field_end: u16,
    ) -> Ext4Result<()> {
        if self.try_expand_extra_isize_for_field(inode, field_end) {
            Ok(())
        } else {
            Err(Ext4Error::unsupported())
        }
    }

    /// Applies a prepared metadata update to an already loaded inode image.
    ///
    /// The update order mirrors Linux-style setattr handling: grow extra inode
    /// space for requested fields, apply identity and mode changes, resolve
    /// timestamps lazily from the device clock, and finally maintain `i_dtime`.
    pub(crate) fn apply_loaded_inode_metadata<B: BlockDevice>(
        &self,
        device: &Jbd2Dev<B>,
        inode: &mut Ext4Inode,
        update: Ext4InodeMetadataUpdate,
    ) -> Ext4Result<()> {
        let inode_size = self.inode_disk_size();

        // Grow `i_extra_isize` only for fields that are actually requested by this update.
        if update.atime.is_some() {
            let _ =
                self.try_expand_extra_isize_for_field(inode, Ext4Inode::FIELD_END_I_ATIME_EXTRA);
        }
        if update.mtime.is_some() {
            let _ =
                self.try_expand_extra_isize_for_field(inode, Ext4Inode::FIELD_END_I_MTIME_EXTRA);
        }
        if update.ctime.is_some() {
            let _ =
                self.try_expand_extra_isize_for_field(inode, Ext4Inode::FIELD_END_I_CTIME_EXTRA);
        }
        if update.crtime.is_some() {
            let _ =
                self.try_expand_extra_isize_for_field(inode, Ext4Inode::FIELD_END_I_CRTIME_EXTRA);
        }

        // Apply mode and ownership updates before timestamp maintenance.
        if let Some(mode) = update.mode {
            match mode {
                Ext4ModeUpdate::Replace(mode) => inode.set_mode_full(mode),
                Ext4ModeUpdate::Chmod(mode) => inode.set_mode_preserve_type(mode),
            }
        }

        if let Some(uid) = update.uid {
            inode.set_uid(uid);
        }
        if let Some(gid) = update.gid {
            inode.set_gid(gid);
        }

        if update.clear_suid_sgid_on_write {
            inode.clear_setid_bits_for_content_change();
        }
        if update.clear_suid_sgid_on_chown {
            inode.clear_setid_bits_for_chown();
        }

        if let Some(projid) = update.projid {
            self.ensure_extra_isize_for_field(inode, Ext4Inode::FIELD_END_I_PROJID)?;
            inode.i_projid = projid;
        }

        // Resolve `Now` only once even when multiple timestamps in the same update need it.
        let mut now_cache: Option<Ext4Timestamp> = None;

        if let Some(spec) = update.atime
            && let Some(ts) = resolve_time_spec(device, spec, &mut now_cache)?
        {
            inode.set_atime_ts(inode_size, ts);
        }

        if let Some(spec) = update.mtime
            && let Some(ts) = resolve_time_spec(device, spec, &mut now_cache)?
        {
            inode.set_mtime_ts(inode_size, ts);
        }

        if let Some(spec) = update.ctime
            && let Some(ts) = resolve_time_spec(device, spec, &mut now_cache)?
        {
            inode.set_ctime_ts(inode_size, ts);
        }

        if let Some(spec) = update.crtime
            && let Some(ts) = resolve_time_spec(device, spec, &mut now_cache)?
        {
            inode.set_crtime_ts(inode_size, ts);
        }

        // `i_dtime` is maintained separately because delete-time semantics do not match normal timestamps.
        match update.dtime {
            Ext4DtimeUpdate::Keep => {}
            Ext4DtimeUpdate::Clear => inode.i_dtime = 0,
            Ext4DtimeUpdate::SetNow => {
                let now = get_now(device, &mut now_cache)?;
                inode.i_dtime = if now.sec <= 0 { 0 } else { now.sec as u32 };
            }
        }

        Ok(())
    }
}