Copy stable/9 to releng/9.3 as part of the 9.3-RELEASE cycle.

Approved by: re (implicit)
Sponsored by: The FreeBSD Foundation

MFC r260229, r260258, r260367, r260390, r260459, r260648:
Rework NFS Duplicate Request Cache cleanup logic.

- Introduce additional hash to group requests by hash of sockref. This
allows to process TCP acknowledgements without looping though all the cache,
and as result allows to do it every time.
- Indroduce additional callbacks to notify application layer about sockets
disconnection. Without this last few requests processed just before socket
disconnection never processed their ACKs and stuck in cache for many hours.
- Implement transport-specific method for tracking reply acknowledgements.
New implementation does not cross multiple stack layers to get the data and
does not have race conditions that previously made some requests stuck
in cache. This could be done more efficiently at sockbuf layer, but that
would broke some KBIs, while I don't know other consumers for it aside NFS.
- Instead of traversing all DRC twice per request, run cleaning only once
per request, and except in some conditions traverse only single hash slot
at a time.

Together this limits NFS DRC growth only to situations of real connectivity
problems. If network is working well, and so all replies are acknowledged,
cache remains almost empty even after hours of heavy load. Without this
change on the same test cache was growing to many thousand requests even
with perfectly working local network.

As another result this reduces CPU time spent on the DRC handling during
SPEC NFS benchmark from about 10% to 0.5%.

Sponsored by: iXsystems, Inc.

MFC r259877:
Slightly simplify expiration logic introduced in r254337.

- Do not update the histogram for items we are any way deleting from cache.
- Do not update the histogram if nfsrc_tcphighwater is not set.
- Remove some extra math operations.

MFC: r254337
Fix several performance related issues in the new NFS server's
DRC for NFS over TCP.
- Increase the size of the hash tables.
- Create a separate mutex for each hash list of the TCP hash table.
- Single thread the code that deletes stale cache entries.
- Add a tunable called vfs.nfsd.tcphighwater, which can be increased
to allow the cache to grow larger, avoiding the overhead of frequent
scans to delete stale cache entries.
(The default value will result in frequent scans to delete stale cache
entries, analagous to what the pre-patched code does.)
- Add a tunable called vfs.nfsd.cachetcp that can be used to disable
DRC caching for NFS over TCP, since the old NFS server didn't DRC cache TCP.
It also adjusts the size of nfsrc_floodlevel dynamically, so that it is
always greater than vfs.nfsd.tcphighwater.

For UDP the algorithm remains the same as the pre-patched code, but the
tunable vfs.nfsd.udphighwater can be used to allow the cache to grow
larger and reduce the overhead caused by frequent scans for stale entries.
UDP also uses a larger hash table size than the pre-patched code.

MFC: r232050
hrs@ reported a panic to freebsd-stable@ under the subject line
"panic in 8.3-PRERELEASE" on Feb. 22, 2012. This panic was caused
by use of a mix of tsleep() and msleep() calls on the same event
in the new NFS server DRC code. It did "mtx_unlock(); tsleep();"
in two places, which kib@ noted introduced a slight risk that the
wakeup() would occur before the tsleep(), resulting in a 10sec
delay before waking up. This patch fixes the problem by replacing
"mtx_unlock(); tsleep();" with mtx_sleep(..PDROP..). It also
changes a nfsmsleep() call to mtx_sleep() so that the code uses
mtx_sleep() consistently within the file.

Copy head to stable/9 as part of 9.0-RELEASE release cycle.

Approved by: re (implicit)

Add DEXITCODE plumbing to NFS.

Isilon has the concept of an in-memory exit-code ring that saves the last exit
code of a function and allows for stack tracing. This is very helpful when
debugging tough issues.

This patch is essentially a no-op for BSD at this point, until we upstream
the dexitcode logic itself. The patch adds DEXITCODE calls to every NFS
function that returns an errno error code. A number of code paths were also
reorganized to have single exit paths, to reduce code duplication.

Submitted by: David Kwan <dkwan@isilon.com>
Reviewed by: rmacklem
Approved by: zml (mentor)
MFC after: 2 weeks

Fix a number of places where the new NFS server did not
lock the mutex when manipulating rc_flag in the DRC cache.
This is believed to fix a hung server that was reported
to the freebsd-fs@ list on June 9 under the subject heading
"New NFS server stress test hang", where all the threads
were waiting for the RC_LOCKED flag to clear.

Tested by: jwd at slowblink.com
MFC after: 2 weeks

Clean up the experimental NFS server replay cache when the module is unloaded.

Reviewed by: rmacklem
Approved by: zml (mentor)

This fixes the experimental NFS server so that it won't crash in the
caching code for IPv6 by fixing a typo that used the incorrect variable.
It also fixes the indentation of the statement above it.

Reported by: simon AT comsys.ntu-kpi.kiev.ua
MFC after: 5 days

Allow using IPv6 in nfsrvd_sentcache() callback.

PR: kern/141289
Submitted by: Petr Lampa <lampa fit vutbr cz>
Approved by: rmacklem
MFC after: 1 week

Add the experimental nfs subtree to the kernel, that includes
support for NFSv4 as well as NFSv2 and 3.
It lives in 3 subdirs under sys/fs:
nfs - functions that are common to the client and server
nfsclient - a mutation of sys/nfsclient that call generic functions
to do RPCs and handle state. As such, it retains the
buffer cache handling characteristics and vnode semantics that
are found in sys/nfsclient, for the most part.
nfsserver - the server. It includes a DRC designed specifically for
NFSv4, that is used instead of the generic DRC in sys/rpc.
The build glue will be checked in later, so at this point, it
consists of 3 new subdirs that should not affect kernel building.

Approved by: kib (mentor)