Copy stable/10@r272459 to releng/10.1 as part of
the 10.1-RELEASE process.

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

Copy head (r256279) to stable/10 as part of the 10.0-RELEASE cycle.

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

Explicitly switch to the new TSS by updating the current CPU's TSS selector
and reloading it in i386_extend_pcb() rather than trying to force a context
switch to reload the TSS via the TDF_NEEDRESCHED flag. Optimizations to
avoid calling cpu_switch() when the new thread was identical to the old
thread defeated the attempt to force a TSS reload. Explicitly loading the
new TSS is what we really want to do anyway.

PR: i386/84842
Reported by: Alexander Best arundel at h3c dot de
MFC after: 1 week
Reviewed by: bde (mostly)

Remove __P.

Split the per-process Local Descriptor Table out of the PCB and into
struct mdproc.

Submitted by: Andrew R. Reiter <arr@watson.org>
Silence on: -current

KSE Milestone 2
Note ALL MODULES MUST BE RECOMPILED
make the kernel aware that there are smaller units of scheduling than the
process. (but only allow one thread per process at this time).
This is functionally equivalent to teh previousl -current except
that there is a thread associated with each process.

Sorry john! (your next MFC will be a doosie!)

Reviewed by: peter@freebsd.org, dillon@freebsd.org

X-MFC after: ha ha ha ha

- Use sched_lock and critical regions to ensure that LDT updates are thread
safe from preemption and concurrent access to the LDT.
- Move the prototype for i386_extend_pcb() to <machine/pcb_ext.h>.

Reviewed by: silence on -hackers

Activate USER_LDT by default. The new thread libraries are going to
depend on this. The linux ABI emulator tries to use it for some linux
binaries too. VM86 had a bigger cost than this and it was made default
a while ago.

Reviewed by: jhb, imp

Change #ifdef KERNEL to #ifdef _KERNEL in the public headers. "KERNEL"
is an application space macro and the applications are supposed to be free
to use it as they please (but cannot). This is consistant with the other
BSD's who made this change quite some time ago. More commits to come.

User ldt sharing.

$Id$ -> $FreeBSD$

A couple of missing doscmd header files. Messed up again. Now can
compile the kernel!!!
Submitted by: Jonathan Lemon <jlemon@americantv.com>