Merge tag '9p-6.4-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/ericvh/v9fs

Pull 9p updates from Eric Van Hensbergen:
 "This includes a number of patches that didn't quite make the cut last
  merge window while we addressed some outstanding issues and review
  comments. It includes some new caching modes for those that only want
  readahead caches and reworks how we do writeback caching so we are not
  keeping extra references around which both causes performance problems
  and uses lots of additional resources on the server.

  It also includes a new flag to force disabling of xattrs which can
  also cause major performance issues, particularly if the underlying
  filesystem on the server doesn't support them.

  Finally it adds a couple of additional mount options to better support
  directio and enabling caches when the server doesn't support
  qid.version.

  There was one late-breaking bug report that has also been included as
  its own patch where I forgot to propagate an embarassing b...