MFC: r337438
Allow newnfs_request() to retry all callback RPCs with an NFSERR_DELAY reply.

The code in newnfs_request() retries RPCs that get a reply of NFSERR_DELAY,
but exempts certain NFSv4 operations. However, for callback RPCs, there
should not be any exemptions at this time. The code would have erroneously
exempted the CBRECALL callback, since it has the same operation number as
the CLOSE operation.
This patch fixes this by checking for a callback RPC (indicated by clp != NULL)
and not checking for exempt operations for callbacks.
This would have only affected the NFSv4 server when delegations are enabled
(they are not enabled by default) and the client replies to CBRECALL with
NFSERR_DELAY. This may never actually happen.
Spotted during code inspection.

MFC: r334966
Add a couple of safety belt checks to the NFSv4.1 client related to sessions.

There were a couple of cases in newnfs_request() that it assumed that it
was an NFSv4.1 mount with a session. This should always be the case when
a Sequence operation is in the reply or the server replies NFSERR_BADSESSION.
However, if a server was broken and sent an erroneous reply, these safety
belt checks should avoid trouble.
The one check required a small tweak to nfsmnt_mdssession() so that it
returns NULL when there is no session instead of the offset of the field
in the structure (0x8 for i386).
This patch should have no effect on normal operation of the client.
Found by inspection during pNFS server development.

MFC: r324506
Fix forced dismount when a pNFS mount is hung on a DS.

When a "pnfs" NFSv4.1 mount is hung because of an unresponsive DS,
a forced dismount wouldn't work, because the RPC socket for the DS
was not being closed. This patch fixes this.
This will only affect "pnfs" mounts where the pNFS server's DS
is unresponsive (crashed or network partitioned or...).
Found during testing of the pNFS server.

MFC: r320062, r320070, r320126
This is a partial merge of only the NFS changes and not the maxbcachebuf
tunable.

The NFS client changes make the code handle different I/O sizes more
correctly. However, with the limit at 64K, they are not actually
necessary.
This MFC is mainly being done so that subsequent MFCs to the NFS
code will merge easily.

MFC: r317276
Don't set ND_NOMOREDATA for a failed Setattr operation (NFSv4).

The NFSv4 Setattr operation always has reply data even when it fails,
so don't set the ND_NOMOREDATA for it. This would only affect unusual
cases where Setattr fails and the RPC code wants to parse the rest of
the compound. Detected during recent development related to the pNFS server.

MFC: r317275, r317344
Don't create a backchannel for a DS connection.

An NFSv4.1 client connection to a Data Server (DS) should not have a
backchannel. This patch fixes the NFSv4.1/pNFS client to not do a backchannel
for this case.
Found during recent testing with the pNFS server under development.

MFC: r310491
Fix NFSv4.1 client recovery from NFS4ERR_BAD_SESSION errors.

For most NFSv4.1 servers, a NFS4ERR_BAD_SESSION error is a rare failure
that indicates that the server has lost session/open/lock state.
However, recent testing by cperciva@ against the AmazonEFS server found
several problems with client recovery from this due to it generating this
failure frequently.
Briefly, the problems fixed are:
- If all session slots were in use at the time of the failure, some processes
would continue to loop waiting for a slot on the old session forever.
- If an RPC that doesn't use open/lock state failed with NFS4ERR_BAD_SESSION,
it would fail the RPC/syscall instead of initiating recovery and then
looping to retry the RPC.
- If a successful reply to an RPC for an old session wasn't processed
until after a new session was created for a NFS4ERR_BAD_SESSION error,
it would erroneously update the new session and corrupt it.
- The use of the first element of the session list in the nfs mount
structure (which is always the current metadata session) was slightly
racey. With changes for the above problems it became more racey, so all
uses of this head pointer was wrapped with a NFSLOCKMNT()/NFSUNLOCKMNT().
- Although the kernel malloc() usually allocates more bytes than requested
and, as such, this wouldn't have caused problems, the allocation of a
session structure was 1 byte smaller than it should have been.
(Null termination byte for the string not included in byte count.)

There are probably still problems with a pNFS data server that fails
with NFS4ERR_BAD_SESSION, but I have no server that does this to test
against (the AmazonEFS server doesn't do pNFS), so I can't fix these yet.

Although this patch is fairly large, it should only affect the handling
of NFS4ERR_BAD_SESSION error replies from an NFSv4.1 server.
Thanks go to cperciva@ for the extension testing he did to help isolate/fix
these problems.

Revert r306659 since the userland changes won't merge and this would
break the build.

MFC: r304026
Update the nfsstats structure to include the changes needed by
the patch in D1626 plus changes so that it includes counts for
NFSv4.1 (and the draft of NFSv4.2).
Also, make all the counts uint64_t and add a vers field at the
beginning, so that future revisions can easily be implemented.
There is code in place to handle the old vesion of the nfsstats
structure for backwards binary compatibility.

Subsequent commits will update nfsstat(8) to use the new fields.

MFC: r268115
Merge the NFSv4.1 server code in projects/nfsv4.1-server over
into head. The code is not believed to have any effect
on the semantics of non-NFSv4.1 server behaviour.
It is a rather large merge, but I am hoping that there will
not be any regressions for the NFS server.

MFC: r257598
During code inspection, I spotted that there was a code path where
CLNT_CONTROL() would be called on "client" after it was
released via CLNT_RELEASE(). It was unlikely that this
code path gets executed and I have not heard of any problem
report caused by this bug. This patch fixes the code so that
this cannot happen.

MFC: r268115
Merge the NFSv4.1 server code in projects/nfsv4.1-server over
into head. The code is not believed to have any effect
on the semantics of non-NFSv4.1 server behaviour.
It is a rather large merge, but I am hoping that there will
not be any regressions for the NFS server.

MFC: r257598
During code inspection, I spotted that there was a code path where
CLNT_CONTROL() would be called on "client" after it was
released via CLNT_RELEASE(). It was unlikely that this
code path gets executed and I have not heard of any problem
report caused by this bug. This patch fixes the code so that
this cannot happen.