#7317 ENOSPC and OSD epoch barrier handling


Related:
https://github.com/ceph/ceph-qa-suite/pull/225
https://github.com/ceph/ceph-client/pull/7
We want to let setattr through so that the client can truncate files shorter — I assume that's why it's not on this list?
But we don't want to let it lengthen them, so we need checks on that in handle_client_setattr.

And we *do* want to block setxattr, so I think it should be on this list?