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

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

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

Approved by: re (implicit)

Place hostnames and similar information fully under the prison system.
The system hostname is now stored in prison0, and the global variable
"hostname" has been removed, as has the hostname_mtx mutex. Jails may
have their own host information, or they may inherit it from the
parent/system. The proper way to read the hostname is via
getcredhostname(), which will copy either the hostname associated with
the passed cred, or the system hostname if you pass NULL. The system
hostname can still be accessed directly (and without locking) at
prison0.pr_host, but that should be avoided where possible.

The "similar information" referred to is domainname, hostid, and
hostuuid, which have also become prison parameters and had their
associated global variables removed.

Approved by: bz (mentor)

Collect N identical (or near identical) mkdumpheader() implementations into
one, as threatened in the comment. Textdump magic can be passed in.

Commit step 1 of the vimage project, (network stack)
virtualization work done by Marko Zec (zec@).

This is the first in a series of commits over the course
of the next few weeks.

Mark all uses of global variables to be virtualized
with a V_ prefix.
Use macros to map them back to their global names for
now, so this is a NOP change only.

We hope to have caught at least 85-90% of what is needed
so we do not invalidate a lot of outstanding patches again.

Obtained from: //depot/projects/vimage-commit2/...
Reviewed by: brooks, des, ed, mav, julian,
jamie, kris, rwatson, zec, ...
(various people I forgot, different versions)
md5 (with a bit of help)
Sponsored by: NLnet Foundation, The FreeBSD Foundation
X-MFC after: never
V_Commit_Message_Reviewed_By: more people than the patch

Use dump_write() instead of direct calls to di->dumper() in textdumps.
Textdumps already do pretty much the same sanity checking, but
abstractions and seatbelts are both useful.

MFC after: 2 months

Refine textdump comments slightly.

MFC after: 3 months

Add textdump(4) facility, which provides an alternative form of kernel
dump using mechanically generated/extracted debugging output rather than
a simple memory dump. Current sources of debugging output are:

- DDB output capture buffer, if there is captured output to save
- Kernel message buffer
- Kernel configuration, if included in kernel
- Kernel version string
- Panic message

Textdumps are stored in swap/dump partitions as with regular dumps, but
are laid out as ustar files in order to allow multiple parts to be stored
as a stream of sequentially written blocks. Blocks are written out in
reverse order, as the size of a textdump isn't known a priori. As with
regular dumps, they will be extracted using savecore(8).

One new DDB(4) command is added, "textdump", which accepts "set",
"unset", and "status" arguments. By default, normal kernel dumps are
generated unless "textdump set" is run in order to schedule a textdump.
It can be canceled using "textdump unset" to restore generation of a
normal kernel dump.

Several sysctls exist to configure aspects of textdumps;
debug.ddb.textdump.pending can be set to check whether a textdump is
pending, or set/unset in order to control whether the next kernel dump
will be a textdump from userspace.

While textdumps don't have to be generated as a result of a DDB script
run automatically as part of a kernel panic, this is a particular useful
way to use them, as instead of generating a complete memory dump, a
simple transcript of an automated DDB session can be captured using the
DDB output capture and textdump facilities. This can be used to
generate quite brief kernel bug reports rich in debugging information
but not dependent on kernel symbol tables or precisely synchronized
source code. Most textdumps I generate are less than 100k including
the full message buffer. Using textdumps with an interactive debugging
session is also useful, with capture being enabled/disabled in order to
record some but not all of the DDB session.

MFC after: 3 months