HEADS UP: NFS changes coming into CURRENT early February

  Hi,

TLDR version:
users of NFS with Kerberos (e.g. running gssd(8)) as well as users of NFS with
TLS (e.g. running rpc.tlsclntd(8) or rpc.tlsservd(8)) as well as users of
network lock manager (e.g. having 'options NFSLOCKD' and running rpcbind(8))
are affected.  You would need to recompile & reinstall both the world and the
kernel together.  Of course this is what you'd normally do when you track
FreeBSD CURRENT, but better be warned.  I will post hashes of the specific
revisions that break API/ABI when they are pushed.

Longer version:
last year I tried to check-in a new implementation of unix(4) SOCK_STREAM and
SOCK_SEQPACKET in d80a97def9a1, but was forced to back it out due to several
kernel side abusers of a unix(4) socket.  The most difficult ones are the NFS
related RPC services, that act as RPC clients talking to an RPC servers in
userland.  Since it is impossible to fully emulate a userland process
connection to a unix(4) socket they need to work with the socket internal
structures bypassing all the normal KPIs and conventions.  Of course they
didn't tolerate the new implementation that totally eliminated intermediate
buffer on the sending side.

While the original motivation for the upcoming changes is the fact that I want
to go forward with the new unix/stream and unix/seqpacket, I also tried to make
kernel to userland RPC better.  You judge if I succeeded or not :) Here are
some highlights:

- Code footprint both in kernel clients and in userland daemons is reduced.
  Example: gssd:    1 file changed, 5 insertions(+), 64 deletions(-)
           kgssapi: 1 file changed, 26 insertions(+), 78 deletions(-)
	            4 files changed, 1 insertion(+), 11 deletions(-)
- You can easily see all RPC calls from kernel to userland with genl(1):
  # genl monitor rpcnl
- The new transport is multithreaded in kernel by default, so kernel clients
  can send a bunch of RPCs without any serialization and if the userland
  figures out how to parallelize their execution, such parallelization would
  happen.  Note: new rpc.tlsservd(8) will use threads.
- One ad-hoc single program syscall is removed - gssd_syscall.  Note:
  rpctls syscall remains, but I have some ideas on how to improve that, too.
  Not at this step though.
- All sleeps of kernel RPC calls are now in single place, and they all have
  timeouts.  I believe NFS services are now much more resilient to hangs.
  A deadlock when NFS kernel thread is blocked on unix socket buffer, and
  the socket can't go away because its application is blocked in some other
  syscall is no longer possible.

The code is posted on phabricator, reviews D48547 through D48552.
Reviewers are very welcome!

I share my branch on Github. It is usually rebased on today's CURRENT:

https://github.com/glebius/FreeBSD/commits/gss-netlink/

Early testers are very welcome!

-- 
Gleb Smirnoff