Re: fanotify read returns with errno == EOPENSTALE

[Marko Rauhamaa <marko.rauhamaa@f-secure.com>]

Jeff Layton <jlayton@poochiereds.net>:

> It was definitely not the intention to leak this error code to
> userland. EOPENSTALE is not a POSIX sanctioned error code, so
> applications generally don't know anything about it and will be
> confused.

Got it. I will try to work on a reproduction and make a proper bug
report.

> I haven't looked closely at this particular problem, but IIRC we
> usually just translate EOPENSTALE to ESTALE, and that may be all that
> needs to be done here. If this happened in the RHEL kernel, then
> please do open a bug with Red Hat and we'll get it straightened out.

ESTALE has not been mentioned as a possible error code from an fanotify
read. Most importantly, since read fails, I suppose there is no recovery
but you must close the fanotify fd and call fanotify_init() again. Or
should I just ignore it and read on? If so, why bother returning the
error from the kernel in the first place?

> That said, you should take heed that all of the [fa|i|d]notify APIs do
> not extend beyond the local machine when you use them on network
> filesystems. If you're expecting to get notification of events that
> are occurring on other clients, you're going to be disappointed here.

That certainly is disappointing. However, there is a certain level of
coherency one would expect, namely:

 * An NFS4 client opening a file should be subject to an OPEN_PERM check
   on that client (if the client is monitoring the mount point).

 * An NFS4 client opening a file should be subject to an OPEN_PERM check
   on the server (if the server is monitoring the mount point).

 * An fanotify read should not fail mysteriously. Rather, a read on
   metadata->fd should be the one failing.


Marko