Function validate_filename 

pub fn validate_filename(filename: &[u8]) -> Result<()>

Validate that filename is an acceptable external filename.

Checks, in order:

1. Not empty.
2. Not longer than MAX_FILENAME_LEN.
3. No embedded NUL bytes.
4. Not an absolute path (does not start with /).
5. No .. path components.

Note that . components and empty components (from //) are permitted, as the kernel will handle them safely.

Errors

Returns Error::InvalidFilename or Error::FilenameTooLong on failure.