Missing tokens should cause a better failure than I/O error

[krichter722]

When a user previously accessed a directory and listed the content, it's possible to open the file with an external application (e.g. a video file with VLC media player). If the user doesn't have a valid token he_she only gets I/O error whereas it'd be more helpful to give a feedback like "Missing authentication token (did you run clog [user]@[realm])?".

experienced with 6.11.2-1+ubuntu16.10 on Ubuntu 16.10

[jaharkes]

The POSIX api doesn't give you that type of flexibility on returning errors from open(2).

As an aside, I'm pretty sure we try to return EPERM when tokens are missing. EIO is typically used for more critical issues, like when your Coda client has crashed and the kernel module is unable to talk to userspace.

There is a feedback channel in the form of 'codacon', which I believe does display some message when tokens have expired, but not when tokens have never been obtained in the first place. I'm pretty sure it does not trigger a message when an access fails because there are no tokens.