MFC r258909:

Tweak mdconfig(8) manual page, in particular revise the EXAMPLES
section. This removes stuff that doesn't really belong there,
and simplifies examples for the basic operations.

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

Make it possible to resize md(4) devices.

Reviewed by: kib
Sponsored by: FreeBSD Foundation

Fix comment.

Rename GEOM class kernel module g_md.ko to geom_md.ko for consistency
with the rest.

mdconfig.c: Simplify mdmaybeload() function.
mdioctl.h: Removed (now unused) #define.
loader.conf: Sort GEOM classes properly.

OK'ed by: phk

/* -> /*- for license, minor formatting changes

Rewrite piece of code which I committed some time ago that allows to
show file name for 'mdconfig -l -u <x>' command.
This allows to preserve API/ABI compatibility with version 0 (that's why
I changed version number back to 0) and will allow to merge this change
to RELENG_5.

MFC after: 5 days

For file backed md(4) devices output their source file via
'mdconfig -l -u <unit>'.
Bump version number, as this change breaks ABI/API.

- Make md(4) 64-bit clean.
After this change it should be possible to use very big md(4) devices.
- Clean up and simplify the code a bit.
- Use humanize_number(3) to print size of md(4) devices.
- Add 't' suffix which stands for terabyte.
- Make '-S' to really work with all types of devices.
- Other minor changes.

change the name of the md module, to g_md, introduce a define with the
name MD_MODNAME, and make mdconfig use this new define...

Remove advertising clause from University of California Regent's license,
per letter dated July 22, 1999.

Approved by: core

Fix a long-standing deadlock issue with vnode backed md(4) devices:

On vnode backed md(4) devices over a certain, currently undetermined
size relative to the buffer cache our "lemming-syncer" can provoke
a buffer starvation which puts the md thread to sleep on wdrain.

This generally tends to grind the entire system to a stop because the
event that is supposed to wake up the thread will not happen until a fair
bit of the piled up I/O requests in the system finish, and since a lot
of those are on a md(4) vnode backed device which is currently waiting
on wdrain until a fair amount of the piled up ... you get the picture.

The cure is to issue all VOP_WRITES on the vnode backing the device
with IO_SYNC.

In addition to more closely emulating a real disk device with a
non-lying write-cache, this makes the writes exempt from rate-limited
(there to avoid starving the buffer cache) and consequently prevents
the deadlock.

Unfortunately performance takes a hit.

Add "async" option to give people who know what they are doing the
old behaviour.

Add a couple of undocumented test options to MD(4) to aid in regression
testting of GEOM.

Add a "-S sectorsize" option to enable Kirk to find a bug :-)

Add an ioctl to return the unit numbers of the configured md devices.

Actually make use of the md_version field of 'struct mdio'. In order
not to needlessly break compatibility, decrement MDIOVERSION to 0.

Approved by: phk

Introduce a force option, MD_FORCE, that instructs the driver to
bypass some extra anti-foot-shooting measures. Currently, its only
effect is to allow detaching a device while it's still open (e.g.,
mounted). This is useful for testing how the system reacts to a disk
suddenly going away, which can happen with some removeable media.

At this point, the force option is only checked on detach, so it
would've been possible to allow the option to be passed with the
MDIOCDETACH operation. This was not done to allow the possibility of
having the force flag influence other tests in the future, which may
not necessarily deal with detaching the device.

Reviewed by: sobomax
Approved by: phk

Make "md" and "mdctl" macroized parameters.

Implement "-l" option to mdconfig which can list one or all md devices.

Submitted by: Dima Dorfman <dima@unixfreak.org>

Add padding space and a version number to the md_ioctl structre for future
extension.

Add ability to create a preload disk giving an address and a length
(suggested by imp)

Fix bug relating to very small md(4) devices.

Update md.c copyright to reflect the status of code copied from vn.c.
(noticed by dillon)

Add compress option at the instigation of rgrimes.

This is repo-copied from vnioctl.h

Fix a bug in the block number calculation for VN disks with a sector
size != 512 that are configured without a label. The bug should only
have effected swap-backed VN mounts without a label.

Add several major features to VN. In the kernel we add a swap
pre-reservation capability, which can be used to guarentee seek
consistency for swap-backed VN nodes. This also incidently allows
a swap-backed VN filesystem to be recovered after a crash in some
cases (if the same swap blocks happen to be reserved).

We also add a number of new options to vnconfig which do the work
of pre-zeroing or creating/truncating/extending a file which greatly
simplifies using VN in a file-backed configuration.

Add FreeBSD CVS label to sys/sys/vnioctl.h, as well as a new ioctl
flag for the swap pre-reservation feature.

Reviewed by: Alan Cox <alc@cs.rice.edu>, David Greenman <dg@root.com>

Reviewed by: julian with quick glances by bruce and others
Submitted by: terry (terry lambert)
This is a composite of 3 patch sets submitted by terry.
they are:
New low-level init code that supports loadbal modules better
some cleanups in the namei code to help terry in 16-bit character support
some changes to the mount-root code to make it a little more
modular..

NOTE: mounting root off cdrom or NFS MIGHT be broken as I haven't been able
to test those cases..

certainly mounting root of disk still works just fine..
mfs should work but is untested. (tomorrows task)

The low level init stuff includes a total rewrite of init_main.c
to make it possible for new modules to have an init phase by simply
adding an entry to a TEXT_SET (or is it DATA_SET) list. thus a new module can
be added to the kernel without editing any other files other than the
'files' file.

A substantial change to the way this works. Not the "TEST_LABELING" is
a option you can turn on and of on the fly, as is debugging.

ioctl definitions for the vn driver.