24-directories.org

Directories

We’ll now add the `mkdir`, `rmdir` and `cd` commands to the shell, and the message handling in the `ramdisk` program to create and delete directories.

Opening read-only

To control whether files and directories can be written we need to be able to open them read-only.

The Rust std::fs::OpenOptions builder provides a way to control the options used when opening a file: Do we want to write the file? If the file exists do we want to create it? etc.

After implementing euralios_std::fs::OpenOptions with the same interface, the fs::create_dir() function is implemented using all our path utilities as:

pub fn create_dir<P: AsRef<Path>>(path: P) -> Result<(), SyscallError> {
    let path: &Path = path.as_ref();

    // Get the directory's parent
    let parent = match path.parent() {
        Some(parent) => parent,
        None => { return Err(syscalls::SYSCALL_ERROR_PARAM); }
    };

    // Get the final part of the path
    let new_dir_name = match path.file_name() {
        Some(name) => name,
        None => { return Err(syscalls::SYSCALL_ERROR_PARAM); }
    };

    // Open the parent directory for modifying
    let f = OpenOptions::new().write(true).open(parent)?;

    // Send a MKDIR message
    let bytes = new_dir_name.bytes();
    match f.rcall(message::MKDIR,
                  (bytes.len() as u64).into(),
                  MemoryHandle::from_u8_slice(bytes).into()) {
        Err((err, _)) => Err(err),
        Ok((message::OK, _, _)) => Ok(()),
        _ => Err(syscalls::SYSCALL_ERROR_PARAM)
    }
}

In the next section we’ll use directories and custom Virtual File Systems (VFS) to isolate multiple users from each other.