Opening a file opens it using the corresponding filesystem. Multiple processes can open the same file in any mode, and the file only leaves the FS cache when no process has it open anymore.
## Minimal FS API
```
trait FileIO {
// reads the whole file
pub fn read(path: Path) -> Vec<u8>
// overwrites the file contents
pub fn write(path: Path, data: Vec<u8>)
// opens a file for reading and writing
pub fn open(path: Path)
// closes a file, removing it from the cache
pub fn close(path: Path)
// deletes a file
pub fn delete(path: Path)
}
```
All filesystems must expose at least these functions in order to work with the VFS.
## Structure
### Mount Point Lookup Entry
```
path_len: u64
path: [u8; <path_len>]
entries: u64
addr: u64
```
There is one of these for each mount point, stored sequentially. The list ends when it finds a path_len of 0
### Sub Part
```
name_len: u64
name: [u8; <name_len>]
dir: u8
size: u64
addr: u64
```
There can be many of these in a mount point, and they can be nested within eachother. dir is 1 if the part is a directory, or 0 if it's a file. size specifies the number of sub parts within a directory, or the number of bytes within a file
