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 r259892:

In sys/kern/vfs_mountroot.c, remove static function parse_isspace(),
which is unused since r214006.

MFC r255412:

In r243868, the error message buffer errmsg have been changed from
an on-stack array to a pointer and therefore sizeof(errmsg) would
become 4 or 8 bytes depending on the architecture.

Fix this by using ERRMSGL in place of sizeof().

Submitted by: J David <j.david.lists@gmail.com>

MFC r253910: Add a tunable for the default timeout.

Requested by: rodrigc@, delphij@

MFC r248645: post mountroot event after a real/final root is mounted

MFC r243868:
Do not allocate buffer of the 255 bytes length on the stack.

MFC r228633,228634,228638,228642,228643: introduce cngets,
a method for kernel to read a string from console

MFC r231949:
Fix found places where uio_resid is truncated to int.

Add the sysctl debug.iosize_max_clamp, enabled by default. Setting the
sysctl to zero allows to perform the SSIZE_MAX-sized i/o requests from
the usermode.

MFC r232493:
Remove unneeded cast to u_int. The values as small enough to fit into
int, beside the use of MIN macro which performs type promotions.

MFC r232494:
Instead of incomplete handling of read(2)/write(2) return values that
does not fit into registers, declare that we do not support this case
using CTASSERT(), and remove endianess-unsafe code to split return value
into td_retval.

While there, change the style of the sysctl debug.iosize_max_clamp
definition.

MFC r232495:
pipe_read(): change the type of size to int, and remove signed clamp.
pipe_write(): change the type of desiredsize back to int, its value fits.

MFC r226673:
Don't terminate the interactive root mount prompt on mount failure.
This restores the previous behaviour. While here, match '?' and '.'
inputs exactly and improve the error message.

Requested by: avg@
Derived from a patch by: Arnaud Lacombe <lacombar@gmail.com>
Approved by: re (kib@)

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

Approved by: re (implicit)

Include sys/sbuf.h directly.

Make RB_CDROM work. This should probably check for a disc in cd1 and acd1
as well.

Add support for asterisk characters when filling in the GELI password
during boot.

Change the last argument of gets() to indicate a visibility flag and add
definitions for the numerical constants. Except for the value 2, gets()
will behave exactly the same, so existing consumers shouldn't break. We
only use it in two places, though.

Submitted by: lme (older version)

ZFS pool name is not a real device in devfs. Do not wait for
device appear when mounting root from ZFS.

Reviewed by: marcel
Approved by: mav (mentor)

Re-implement the root mount logic using a recursive approach, whereby each
root file system (starting with devfs and a synthesized configuration) can
contain directives for mounting another file system as root. The old root
file system is re-mounted under the new root file system (with /.mount or
/mnt as the mount point) to allow access to the underlying file system.

The configuration allows for creating vnode-backed memory disks that can
subsequently be mounted as root. This allows for an efficient and low-
cost way to distribute and boot FreeBSD software images that reside on
some storage media.

When trying a mount, the kernel will wait for the device in question to
arrive. The timeout is configurable and is part of the configuration.
This allows arbitrarily complex GEOM configurations to be constructed
on the fly.

A side-effect of this change is that all root specifications, whether
compiled into the kernel or typed at the prompt can contain root mount
options.

Split the root mount logic from the (generic) mount code and move
it (the root mount code) into a new file called vfs_mountroot.c

The split is almost trivial, as the code is almost perfectly
non-intertwined. The only adjustment needed was to move the UMA
zone allocation out of vfs_mountroot() [in vfs_mountroot.c] and
into vfs_mount.c, where it had to be done as a SYSINIT [see
vfs_mount_init()].

There are no functional changes with this commit.