Summary:
This header uses various types that come from here regardless of whether
_KERNEL is defined, so unconditionally include it rather than relying on
other headers implicitly including it for when _KERNEL is not defined.

Subscribers: imp

Differential Revision: https://reviews.freebsd.org/D50884

Reviewers: imp, kib, markj, mjg

Differential Revision: https://reviews.freebsd.org/D50716

Summary:
This allows struct iso_mnt to be defined for userspace without resorting
to the gross hack of defining _KERNEL.

Reviewers: imp, kib, markj

Differential Revision: https://reviews.freebsd.org/D50717

Summary:
Whilst these aren't used by makefs, they do little harm existing once
the needed headers are included, and having structs change layout based
on defines like this can be fraught. This will be particularly true once
this code is exposed by defines other than _KERNEL and MAKEFS, as any
consumer will be able to opt into exposing this kernel type and all the
definitions should match.

Subscribers: imp

Differential Revision: https://reviews.freebsd.org/D50885

Summary:
This lets other bits of userspace expose these various definitions too.
The function prototypes surely won't be useful in other contexts, but
the various types are, and it's not worth hiding the prototypes unless
they end up causing issues, but so long as they aren't called they
shouldn't be a problem.

Note the MAKEFS define continues to exist, but only for use in
newfs_msdos, as those sources are reused by makefs with some changed
behaviour.

Test Plan: imp, kib, markj

Subscribers: imp

Differential Revision: https://reviews.freebsd.org/D50718

Summary:
Defining _KERNEL is a historical hack that can often break due to the
environment not actually being that of a kernel build. Now that we have
other targeted macros we can define instead that don't have far-reaching
implications like _KERNEL we can drop this.

Reviewers: imp, kib, markj

Differential Revision: https://reviews.freebsd.org/D50719

…erspace

Summary:
Note that ZNODE_OS_FIELDS needs to change to using struct vnode over
vnode_t (matching struct zfsvfs rather than vnode_t) since vnode_t is
only defined in the kernel SPL, not the userspace SPL (libspl).

Reviewers: imp, kib, markj, mm

Subscribers: delphij

Differential Revision: https://reviews.freebsd.org/D50720

Summary:
Now that we have a _WANT_ZNODE we can use that instead of defining
_KERNEL, and we're able to move the code back into zfs.c using a real
znode_t pointer.

Reviewers: imp, kib, markj, mm

Subscribers: delphij

Differential Revision: https://reviews.freebsd.org/D50721

These will be needed by future changes to continue to allow building
makefs as a bootstrap tool on Linux and macOS. This also requires
defining __sbintime_t in our cross-build sys/_types.