dtoolkit 0.1.1

A library for parsing and manipulating Flattened Device Tree (FDT) blobs.
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
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227

// Copyright 2025 Google LLC
//
// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
// https://www.apache.org/licenses/LICENSE-2.0> or the MIT license
// <LICENSE-MIT or https://opensource.org/licenses/MIT>, at your
// option. This file may not be copied, modified, or distributed
// except according to those terms.

use alloc::borrow::ToOwned;
use alloc::collections::btree_map::BTreeMap;
use alloc::string::String;
use alloc::vec::Vec;

use zerocopy::IntoBytes;

use crate::fdt::{
    FDT_BEGIN_NODE, FDT_END, FDT_END_NODE, FDT_MAGIC, FDT_PROP, FDT_TAGSIZE, Fdt, FdtHeader,
};
use crate::memreserve::MemoryReservation;
use crate::model::{DeviceTree, DeviceTreeNode, DeviceTreeProperty};
use crate::{Node, Property};

// https://devicetree-specification.readthedocs.io/en/latest/chapter5-flattened-format.html#header
const LAST_VERSION: u32 = 17;
const LAST_COMP_VERSION: u32 = 16;

impl DeviceTree {
    /// Serializes the [`DeviceTree`] to a flattened device tree blob.
    ///
    /// # Panics
    ///
    /// This may panic if any of the lengths written to the DTB (block sizes,
    /// property value length, etc.) exceed [`u32::MAX`].
    #[must_use]
    pub fn to_dtb(&self) -> Vec<u8> {
        let mut string_map = StringMap::new();
        let header = self.generate_header(&mut string_map);

        let mut dtb = Vec::with_capacity(header.totalsize() as usize);
        dtb.extend_from_slice(header.as_bytes());

        self.write_memory_reservations(&mut dtb);
        self.write_root(&mut dtb, &string_map);
        string_map.write_string_block(&mut dtb);

        debug_assert_eq!(
            dtb.len(),
            header.totalsize() as usize,
            "calculated buffer size was not big enough"
        );

        dtb
    }

    /// Calculate all needed sizes (so that we can pre-allocate the buffer) and
    /// return [`FdtHeader`].
    #[must_use]
    fn generate_header(&self, string_map: &mut StringMap) -> FdtHeader {
        // entries + terminator
        let mem_reservations_size =
            (self.memory_reservations.len() + 1) * size_of::<MemoryReservation>();
        // +FDT_TAGSIZE for FDT_END
        let dt_struct_size = Self::calculate_node_size(string_map, &self.root) + FDT_TAGSIZE;
        let dt_strings_size = string_map.next_offset as usize;

        let header_size = size_of::<FdtHeader>();
        let off_mem_rsvmap = header_size;
        let off_dt_struct = off_mem_rsvmap + mem_reservations_size;
        let off_dt_strings = off_dt_struct + dt_struct_size;
        let totalsize = off_dt_strings + dt_strings_size;

        let size_dt_strings = totalsize - off_dt_strings;
        let size_dt_struct = off_dt_strings - off_dt_struct;

        FdtHeader {
            magic: FDT_MAGIC.into(),
            totalsize: u32::try_from(totalsize)
                .expect("totalsize exceeds u32")
                .into(),
            off_dt_struct: u32::try_from(off_dt_struct)
                .expect("off_dt_struct exceeds u32")
                .into(),
            off_dt_strings: u32::try_from(off_dt_strings)
                .expect("off_dt_strings exceeds u32")
                .into(),
            off_mem_rsvmap: u32::try_from(off_mem_rsvmap)
                .expect("off_mem_rsvmap exceeds u32")
                .into(),
            version: LAST_VERSION.into(),
            last_comp_version: LAST_COMP_VERSION.into(),
            boot_cpuid_phys: 0u32.into(),
            size_dt_strings: u32::try_from(size_dt_strings)
                .expect("size_dt_strings exceeds u32")
                .into(),
            size_dt_struct: u32::try_from(size_dt_struct)
                .expect("size_dt_struct exceeds u32")
                .into(),
        }
    }

    fn calculate_node_size(string_map: &mut StringMap, node: &DeviceTreeNode) -> usize {
        let mut size = 0;
        size += FDT_TAGSIZE; // FDT_BEGIN_NODE

        // name + null terminator + padding
        let name_len = node.name().len() + 1;
        size += Fdt::align_tag_offset(name_len);

        for prop in node.properties() {
            size += Self::calculate_prop_size(string_map, prop);
        }

        for child in node.children() {
            size += Self::calculate_node_size(string_map, child);
        }

        size += FDT_TAGSIZE; // FDT_END_NODE
        size
    }

    fn calculate_prop_size(string_map: &mut StringMap, prop: &DeviceTreeProperty) -> usize {
        let mut size = 0;
        size += FDT_TAGSIZE; // FDT_PROP
        size += size_of::<u32>(); // len
        size += size_of::<u32>(); // nameoff

        // ensure the name is in the map
        string_map.insert(prop.name());

        // value + padding
        size += Fdt::align_tag_offset(prop.value().len());
        size
    }

    fn write_memory_reservations(&self, dtb: &mut Vec<u8>) {
        for reservation in &self.memory_reservations {
            dtb.extend_from_slice(reservation.as_bytes());
        }
        dtb.extend_from_slice(MemoryReservation::TERMINATOR.as_bytes());
    }

    fn write_root(&self, dtb: &mut Vec<u8>, string_map: &StringMap) {
        Self::write_node(dtb, string_map, &self.root);
        dtb.extend_from_slice(&FDT_END.to_be_bytes());
    }

    fn write_node(dtb: &mut Vec<u8>, string_map: &StringMap, node: &DeviceTreeNode) {
        dtb.extend_from_slice(&FDT_BEGIN_NODE.to_be_bytes());
        dtb.extend_from_slice(node.name().as_bytes());
        dtb.push(0);
        Self::align(dtb);

        for prop in node.properties() {
            Self::write_prop(dtb, string_map, prop);
        }

        for child in node.children() {
            Self::write_node(dtb, string_map, child);
        }

        dtb.extend_from_slice(&FDT_END_NODE.to_be_bytes());
    }

    fn write_prop(dtb: &mut Vec<u8>, string_map: &StringMap, prop: &DeviceTreeProperty) {
        let name_offset = string_map.get_offset(prop.name());

        dtb.extend_from_slice(&FDT_PROP.to_be_bytes());
        dtb.extend_from_slice(
            &u32::try_from(prop.value().len())
                .expect("property value length exceeds u32")
                .to_be_bytes(),
        );
        dtb.extend_from_slice(&name_offset.to_be_bytes());
        dtb.extend_from_slice(prop.value());
        Self::align(dtb);
    }

    fn align(vec: &mut Vec<u8>) {
        let len = vec.len();
        let new_len = Fdt::align_tag_offset(len);
        vec.resize(new_len, 0);
    }
}

struct StringMap {
    string_map: BTreeMap<String, u32>,
    next_offset: u32,
}

impl StringMap {
    #[must_use]
    fn new() -> Self {
        Self {
            string_map: BTreeMap::new(),
            next_offset: 0,
        }
    }

    fn insert(&mut self, key: &str) {
        if !self.string_map.contains_key(key) {
            let offset = self.next_offset;
            self.string_map.insert(key.to_owned(), offset);
            self.next_offset = u32::try_from(self.next_offset as usize + key.len() + 1)
                .expect("string block length exceeds u32");
        }
    }

    #[must_use]
    fn get_offset(&self, key: &str) -> u32 {
        *self
            .string_map
            .get(key)
            .expect("the key should have been inserted at the size calculation step")
    }

    fn write_string_block(self, dtb: &mut Vec<u8>) {
        // write the strings in the order when they appear, mimicking the behavior
        // of `dtc` (Device Tree Compiler)
        let mut items: Vec<_> = self.string_map.into_iter().collect();
        items.sort_unstable_by_key(|(_s, offset)| *offset);

        for (s, _offset) in items {
            dtb.extend_from_slice(s.as_bytes());
            dtb.push(0);
        }
    }
}