Changes to the readfile function (error handling for read() ) may be tricky though.
As you'd have to check lots of functionality like when it's really an error or
just eof and what error code you forward to dos.

no error checking.
Only checking the stored file flags for wether it is read_write or read. inside LocalFile::Read

we should be checking what cdroms do though. mscdex might mess around with the flags

A cdrom's file open command should reject write-only calls any way, but only mscdex knows for sure.