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 r239106:

Make sure the compiler knows g_gate_xvlog() and g_gate_xlog() do not
return. This silences a warning from clang 3.2 about uninitialized use
of the variable 'mediasize' in sbin/ggate/shared/ggate.c.

Reviewed by: pjd

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

Approved by: re (implicit)

Style nits.

Implement a work-around for poor ggate write performance.

For consistency use 'unsigned' instead of 'u_int'.

Fix ggated for platforms with 64bit size_t. The DIOCGSECTORSIZE ioctl
returns u_int.

Reported by: Javier Martín Rueda <jmrueda@diatel.upm.es>
PR: amd64/91799
MFC after: 3 days

- Handle timeouts from recv(2) properly.
- Increase timeout to 8 seconds (should be made configurable).

Reported by: Ulrich Spoerlein <uspoerlein@gmail.com>
Reported by: Christian Laursen <xi@borderworlds.dk>
PR: kern/104829
MFC after: 1 week

Reimplement ggatec/ggated applications.

Change communication protocol to be much more resistant on network
problems and to allow for much better performance.

Better performance is achieved by creating two connections between
ggatec and ggated one for sending the data and one for receiving it.
Every connection is handled by separeted thread, so there is no more
synchronous data flow (send and wait for response), now one threads
sends all requests and another receives the data.

Use two threads in ggatec(8):
- sendtd, which takes I/O requests from the kernel and sends them to the
ggated daemon on the other end;
- recvtd, which waits for ggated responses and forwards them to the kernel.

Use three threads in ggated(8):
- recvtd, which waits for I/O requests and puts them onto incoming queue;
- disktd, which takes requests from the incoming queue, does disk operations
and puts finished requests onto outgoing queue;
- sendtd, which takes finished requests from the outgoing queue and sends
responses back to ggatec.

Because there were major changes in communication protocol, there is no
backward compatibility, from now on, both client and server has to run
on 5.x or 6.x (or at least ggated should be from the same FreeBSD version
on which ggatec is running).

For Gbit networks some buffers need to be increased. I use those settings:
kern.ipc.maxsockbuf=16777216
net.inet.tcp.sendspace=8388608
net.inet.tcp.recvspace=8388608
and I use '-S 4194304 -R 4194304' options for both, ggatec and ggated.

Approved by: re (scottl)

include stdarg.h for va_list

Fix/clean up return values checking.

Print mediasize in human readable form as well.

Fix compiling on 64-bit architectures.

Stuff shared between ggate utilities.