1 /*
2 * Copyright (C) 2021 The Android Open Source Project
3 *
4 * Licensed under the Apache License, Version 2.0 (the "License");
5 * you may not use this file except in compliance with the License.
6 * You may obtain a copy of the License at
7 *
8 * http://www.apache.org/licenses/LICENSE-2.0
9 *
10 * Unless required by applicable law or agreed to in writing, software
11 * distributed under the License is distributed on an "AS IS" BASIS,
12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13 * See the License for the specific language governing permissions and
14 * limitations under the License.
15 */
16
17 //! `append_squashfs_overlay` generates a new squashfs image(dest) which contains an overlay image(overlay) on an squashfs image(src).
18 //! The tool ignores the existing overlay image in src, that is, the overlay image could be replaced with a new overlay image.
19 use std::fs::File;
20 use std::io::{copy, Error, ErrorKind, Read, Result, Seek, SeekFrom};
21 use std::path::Path;
22
23 use clap::{App, Arg};
24
25 // https://dr-emann.github.io/squashfs/squashfs.html
26 const BYTES_USED_FIELD_POS: u64 = (32 * 5 + 16 * 6 + 64) / 8;
27 const SQUASHFS_MAGIC: u32 = 0x73717368;
28
29 // https://git.openwrt.org/?p=project/fstools.git;a=blob;f=libfstools/rootdisk.c;h=9f2317f14e8d8f12c71b30944138d7a6c877b406;hb=refs/heads/master#l125
30 // 64kb alignment
31 const ROOTDEV_OVERLAY_ALIGN: u64 = 64 * 1024;
32
align_size(size: u64, alignment: u64) -> u6433 fn align_size(size: u64, alignment: u64) -> u64 {
34 assert!(
35 alignment > 0 && (alignment & (alignment - 1) == 0),
36 "alignment should be greater than 0 and a power of 2."
37 );
38 (size + (alignment - 1)) & !(alignment - 1)
39 }
40
merge_fs(src: &Path, overlay: &Path, dest: &Path, overwrite: bool) -> Result<()>41 fn merge_fs(src: &Path, overlay: &Path, dest: &Path, overwrite: bool) -> Result<()> {
42 if dest.exists() && !overwrite {
43 return Err(Error::new(
44 ErrorKind::AlreadyExists,
45 "The destination file already exists, add -w option to overwrite.",
46 ));
47 }
48 let mut buffer = [0; 4];
49
50 let mut src = File::open(src)?;
51
52 src.read_exact(&mut buffer)?;
53 let magic = u32::from_le_bytes(buffer);
54 if magic != SQUASHFS_MAGIC {
55 return Err(Error::new(ErrorKind::InvalidData, "The source image isn't a squashfs image."));
56 }
57 src.seek(SeekFrom::Start(BYTES_USED_FIELD_POS))?;
58 let mut buffer = [0; 8];
59 src.read_exact(&mut buffer)?;
60
61 // https://git.openwrt.org/?p=project/fstools.git;a=blob;f=libfstools/rootdisk.c;h=9f2317f14e8d8f12c71b30944138d7a6c877b406;hb=refs/heads/master#l125
62 // use little endian
63 let bytes_used = u64::from_le_bytes(buffer);
64 let mut dest = File::create(dest)?;
65 let mut overlay = File::open(overlay)?;
66
67 src.seek(SeekFrom::Start(0))?;
68 let mut src_handle = src.take(align_size(bytes_used, ROOTDEV_OVERLAY_ALIGN));
69 copy(&mut src_handle, &mut dest)?;
70 copy(&mut overlay, &mut dest)?;
71 Ok(())
72 }
73
main() -> Result<()>74 fn main() -> Result<()> {
75 let matches = App::new("append_squashfs_overlay")
76 .arg(Arg::with_name("src").required(true))
77 .arg(Arg::with_name("overlay").required(true))
78 .arg(Arg::with_name("dest").required(true))
79 .arg(
80 Arg::with_name("overwrite")
81 .short("w")
82 .required(false)
83 .takes_value(false)
84 .help("whether the tool overwrite dest or not"),
85 )
86 .get_matches();
87
88 let src = matches.value_of("src").unwrap().as_ref();
89 let overlay = matches.value_of("overlay").unwrap().as_ref();
90 let dest = matches.value_of("dest").unwrap().as_ref();
91 let overwrite = matches.is_present("overwrite");
92
93 merge_fs(src, overlay, dest, overwrite)?;
94 Ok(())
95 }
96