Function finalize_filesystem

crates/lib/src/install.rs:1409–1442

Trim, flush outstanding writes, and freeze/thaw the target mounted filesystem; these steps prepare the filesystem for its first booted use.

(
    fsname: &str,
    root: &Dir,
    path: impl AsRef<Utf8Path>,
)

/// Trim, flush outstanding writes, and freeze/thaw the target mounted filesystem;
/// these steps prepare the filesystem for its first booted use.
pub(crate) fn finalize_filesystem(
    fsname: &str,
    root: &Dir,
    path: impl AsRef<Utf8Path>,
) -> Result<()> {
    let path = path.as_ref();
    // fstrim ensures the underlying block device knows about unused space
    Task::new(format!("Trimming {fsname}"), "fstrim")
        .args(["--quiet-unsupported", "-v", path.as_str()])
        .cwd(root)?
        .run()?;
    // Remounting readonly will flush outstanding writes and ensure we error out if there were background
    // writeback problems.
    Task::new(format!("Finalizing filesystem {fsname}"), "mount")
        .cwd(root)?
        .args(["-o", "remount,ro", path.as_str()])
        .run()?;
    // Finally, freezing (and thawing) the filesystem will flush the journal, which means the next boot is clean.
    // VFAT has no journal and does not support fsfreeze. Might need to be expanded in the future
    // to also *not* fsfreeze other filesystems.
    let fsdir = root.open_dir(path.as_str())?;
    let st = rustix::fs::fstatfs(fsdir.as_fd())?;
    if st.f_type == libc::MSDOS_SUPER_MAGIC {
        tracing::debug!("Filesystem {fsname} is VFAT, skipping fsfreeze");
    } else {
        for a in ["-f", "-u"] {
            Command::new("fsfreeze")
                .cwd_dir(root.try_clone()?)
                .args([a, path.as_str()])
                .run_capture_stderr()?;
        }
    }
    Ok(())
}

/// A heuristic check that we were invoked with --pid=host
fn require_host_pidns() -> Result<()> {