MFC r283291: don't use CALLOUT_MPSAFE with callout_init()

The main purpose of this MFC is to reduce conflicts for other merges.
Parts of the original change have already "trickled down" via individual MFCs.

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

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

rename scheduler->swapper and SI_SUB_RUN_SCHEDULER->SI_SUB_LAST

Also directly call swapper() at the end of mi_startup instead of
relying on swapper being the last thing in sysinits order.

Rationale:

- "RUN_SCHEDULER" was misleading, scheduling already takes place at that stage
- "scheduler" was misleading, the function swaps in the swapped out processes
- another SYSINIT(SI_SUB_RUN_SCHEDULER, SI_ORDER_ANY) could never be
invoked depending on its relative order with scheduler; this was not obvious
and the bug actually used to exist

Reviewed by: kib (ealier version)
MFC after: 14 days

Update the ddb and gdb backends for the new 'trace_thread' hook.
It is implemented via db_trace_thread() for DDB and not implemented
for GDB. This should have been part of r234190.

Pointy hat to: jhb
Reported by: jkim
MFC after: 1 week

kern cons: introduce infrastructure for console grabbing by kernel

At the moment grab and ungrab methods of all console drivers are no-ops.

Current intended meaning of the calls is that the kernel takes control of
console input. In the future the semantics may be extended to mean that
the calling thread takes full ownership of the console (e.g. console
output from other threads could be suspended).

Inspired by: bde
MFC after: 2 months

Modify kdb_trap() so that it re-calls the dbbe_trap function as long as
the debugger back-end has changed. This means that switching from ddb
to gdb no longer requires a "step" which can be dangerous on an
already-crashed kernel.

Also add a capability to get from the gdb back-end back to ddb, by
typing ^C in the console window.

While here, simplify kdb_sysctl_available() by using
sbuf_new_for_sysctl(), and use strlcpy() instead of strncpy() since the
strlcpy semantic is desired.

MFC after: 1 month

there must be only one SYSINIT with SI_SUB_RUN_SCHEDULER+SI_ORDER_ANY order

SI_SUB_RUN_SCHEDULER+SI_ORDER_ANY should only be used to call
scheduler() function which turns the initial thread into swapper proper
and thus there is no further SYSINIT processing.
Other SYSINITs with SI_SUB_RUN_SCHEDULER+SI_ORDER_ANY may get ordered
after scheduler() and thus never executed. That particular relative
order is semi-arbitrary.

Thus, change such places to use SI_ORDER_MIDDLE.
Also, use SI_ORDER_MIDDLE instead of correct, but less appealing,
SI_ORDER_ANY - 1.

MFC after: 1 week

Commit SYSINIT() ;-adding patch missed in previous pass.

MFC after: 1 month
Caught by: tinderbox

Add support for kgdb's 'detach' command.

Reviewed by: marcel
Sponsored by: Network Appliance

Add kdb_cpu_sync_icache(), intended to synchronize instruction
caches with data caches after writing to memory. This typically
is required to make breakpoints work on ia64 and powerpc. For
those architectures the function is implemented.

Convert to new console api

Eliminate gdb_checkc member from GDB_DBGPORT(), it is never used.

Use polling behaviour for gdb_getc() where convenient, this edges us
closer to the console code.

Don't use GDB_DBGPORT() macro to fill in dummy element in gdb_dbgport_set.

Wrap our drivers gdb_getc() function so that if it returns -1 we
try again. This way it matches the console behaviour and allows us
to share more code.

add support for copying console messages to a remote gdb

Reviewed by: kan

check return value of gdb_rx_varhex

Noticed by: Coverity Prevent analysis tool
Reviewed by: kan

/* -> /*- for copyright notices, minor format tweaks as necessary

Change gdb_cpu_setreg() to not take the value to which to set the
specified register, but a pointer to the in-memory representation of
that value. The reason for this is twofold:
1. Not all registers can be represented by a register_t. In particular
FP registers fall in that category. Passing the new register value
by reference instead of by value makes this point moot.
2. When we receive a G or P packet, both are for writing a register,
the packet will have the register value in target-byte order and
in the memory representation (modulo the fact that bytes are sent
as 2 printable hexadecimal numbers of course). We only need to
decode the packet to have a pointer to the register value.

This change fixes the bug of extracting the register value of the P
packet as a hexadecimal number instead of as a bit array. The quick
(and dirty) fix to bswap the register value in gdb_cpu_setreg() as
it has been added on i386 and amd64 can therefore be removed and has
in fact been that.

Tested on: alpha, amd64, i386, ia64, sparc64

Comment-out the debugging printf I left in in case there were some
packet related problems. No problems have been reported.

Introduce the GDB debugger backend for the new KDB framework. The
backend improves over the old GDB support in the following ways:
o Unified implementation with minimal MD code.
o A simple interface for devices to register themselves as debug
ports, ala consoles.
o Compression by using run-length encoding.
o Implements GDB threading support.