Function atomic_swap_dirs_fsync

nodedb-wal/src/segment/atomic_io.rs:76–88

Atomically swap a directory: `rename(live, backup); rename(staged, live)`, fsyncing the parent directory once both renames have completed. `live`, `backup`, and `staged` MUST share the same parent directory. The caller is responsible for removing the backup directory once the new state is proven good — this helper does not delete anything.

(live: &Path, backup: &Path, staged: &Path)

/// caller is responsible for removing the backup directory once the new
/// state is proven good — this helper does not delete anything.
pub fn atomic_swap_dirs_fsync(live: &Path, backup: &Path, staged: &Path) -> Result<()> {
    let parent = live.parent().ok_or_else(|| {
        WalError::Io(std::io::Error::new(
            std::io::ErrorKind::InvalidInput,
            "atomic_swap_dirs_fsync: live has no parent directory",
        ))
    })?;

    fs::rename(live, backup).map_err(WalError::Io)?;
    fs::rename(staged, live).map_err(WalError::Io)?;
    fsync_directory(parent)?;
    Ok(())
}

/// Read a checkpoint file and advise the kernel to drop its pages from the
/// page cache.