btrfs_cli/filesystem/
mkswapfile.rs

1use crate::{
2    Format, Runnable,
3    util::{ParsedUuid, parse_size_with_suffix},
4};
5use anyhow::{Context, Result};
6use clap::Parser;
7use nix::{
8    fcntl::{FallocateFlags, fallocate},
9    libc,
10};
11use std::{
12    fs::{File, OpenOptions},
13    os::unix::{
14        fs::{FileExt, OpenOptionsExt},
15        io::AsRawFd,
16    },
17    path::PathBuf,
18};
19use uuid::Uuid;
20
21const FS_NOCOW_FL: libc::c_long = 0x0080_0000;
22const MIN_SWAP_SIZE: u64 = 40 * 1024;
23
24/// Create a swapfile on a btrfs filesystem
25#[derive(Parser, Debug)]
26pub struct FilesystemMkswapfileCommand {
27    /// Size of the swapfile
28    #[clap(long, short, default_value = "2G")]
29    pub size: String,
30
31    /// UUID to embed in the swap header (clear, random, time, or explicit UUID;
32    /// default: random)
33    #[clap(long = "uuid", short = 'U')]
34    pub uuid: Option<ParsedUuid>,
35
36    /// Path to the swapfile to create
37    pub path: PathBuf,
38}
39
40fn system_page_size() -> Result<u64> {
41    let size = unsafe { libc::sysconf(libc::_SC_PAGESIZE) };
42    anyhow::ensure!(size > 0, "failed to get system page size");
43    Ok(size as u64)
44}
45
46fn write_swap_header(
47    file: &File,
48    page_count: u32,
49    uuid: &Uuid,
50    page_size: u64,
51) -> Result<()> {
52    let mut header = vec![0u8; page_size as usize];
53    header[0x400] = 0x01;
54    header[0x404..0x408].copy_from_slice(&page_count.to_le_bytes());
55    header[0x40c..0x41c].copy_from_slice(uuid.as_bytes());
56    let sig_offset = page_size as usize - 10;
57    header[sig_offset..].copy_from_slice(b"SWAPSPACE2");
58    file.write_at(&header, 0)
59        .context("failed to write swap header")?;
60    Ok(())
61}
62
63impl Runnable for FilesystemMkswapfileCommand {
64    fn run(&self, _format: Format, _dry_run: bool) -> Result<()> {
65        let size = parse_size_with_suffix(&self.size)
66            .with_context(|| format!("invalid size: '{}'", self.size))?;
67
68        let page_size = system_page_size()?;
69
70        anyhow::ensure!(
71            size >= MIN_SWAP_SIZE,
72            "swapfile needs to be at least 40 KiB, got {size} bytes"
73        );
74
75        let uuid = self.uuid.as_deref().copied().unwrap_or_else(Uuid::new_v4);
76
77        let size = size - (size % page_size);
78        let total_pages = size / page_size;
79
80        anyhow::ensure!(
81            total_pages > 10,
82            "swapfile too small after page alignment"
83        );
84
85        let page_count = total_pages - 1;
86        anyhow::ensure!(
87            u32::try_from(page_count).is_ok(),
88            "swapfile too large: page count exceeds u32"
89        );
90
91        let file = OpenOptions::new()
92            .read(true)
93            .write(true)
94            .create_new(true)
95            .mode(0o600)
96            .open(&self.path)
97            .with_context(|| {
98                format!("failed to create '{}'", self.path.display())
99            })?;
100
101        let ret = unsafe {
102            libc::ioctl(file.as_raw_fd(), libc::FS_IOC_SETFLAGS, &FS_NOCOW_FL)
103        };
104        nix::errno::Errno::result(ret)
105            .context("failed to set NOCOW attribute")?;
106
107        fallocate(&file, FallocateFlags::empty(), 0, size as libc::off_t)
108            .context("failed to allocate space for swapfile")?;
109
110        write_swap_header(&file, page_count as u32, &uuid, page_size)?;
111
112        println!(
113            "created swapfile '{}' size {} bytes",
114            self.path.display(),
115            crate::util::human_bytes(size),
116        );
117
118        Ok(())
119    }
120}
btrfs_cli/filesystem/mkswapfile.rs

btrfs_cli/filesystem/
mkswapfile.rs
