VFS messages:
register_fs(mb_no: MailboxID, name: &str) -> bool
mount(dev_path: &str, mount_path: &str, fs: &str) -> bool
open(path: &str, mode: &str) -> (MailboxID, u32)

FS Api:
// Optional mailbox is redirect mailbox - direct file API calls there for provided FD
open(path: &str, mode: &str) -> (Option<MailboxID>, u32)

File Api:
read(fd: u32, pos: usize, len: usize) -> Vec<u8>

DevFS:
register_dev(mb_no: MailboxID, name: &str, kind: u8) -> bool