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)

Fix some style(9), although there's a lot more issues here.
Fix some casting errors.

PR: 142384
Submitted by: giffunip at tutopia dot com
Obtained from: NetBSD
MFC after: 3 weeks

Rename fields to match better the msdosfs headers. This work is still
incomplete as some info doesn't really belong to the structs where it is
defined.

Submitted by: Pedro F. Giffuni <giffunip tutopia com>
Reviewed by: bde
MFC after: 2 weeks

Bug fixes from NetBSD
- fix sign-compare issues.
- ANSIfy a couple of functions.
- Remove more duplicate #includes.
- Memory leak found by Coverity on NetBSD.

Submitted by: Pedro F. Giffuni <giffunip tutopia com>
Reviewed by: bde
MFC after: 2 weeks

License changes from NetBSD.
Move to 2 clause license, approved by Wolfgang Solfrank.

Submitted by: Pedro F. Giffuni <giffunip tutopia com>
MFC after: 2 weeks

Spot two more bugs WRT adherence to the local prompt style.

Use consistent style in user prompts: the question is in a new line
and begins with a capital letter. The rest of pwarn/ask pairs here
follows this style.

Requested by: bde

Fixed some bugs in checkdirty(). The check for the clean bit was
combined with the the signature check in a wrong way (basically
(dirty:= signature_recognised() && !clean) instead of
(mightbedirty:= !signature_recognized || !clean), so file systems
with unrecognized signatures were considered clean. Many of the
don't-care and reserved bits were not ignored, so some file systems
with valid signatures were unrecognized. One of my FAT32 file systems
has a signature of f8,ff,ff,ff,ff,ff,ff,f7 when dirty, but only
f8,ff,ff,0f,ff,ff,ff,07 was recognised as dirty for FAT32, so the
fail-unsafeness made my file system always considered clean.

Check the i/o non-error bit in checkdirty(). Its absence would give
an unrecognized signature in code that is unaware of it, but we now
mask it out of the signature so we have to check it explicitly. This
combines naturally with the check of the clean bit.

Reviewed by: rnordier (except for final details)

Document the dirty flag and other bits in the first 2 FAT entries
better. There is a related I/O error flag which we don't support in
the kernel but must support here. (Support for bits that we don't
understand here is mostly automatic by fail-safeness, but checkdirty()
has fail-unsafeness.) There are some reserved and don't-care bits
that weren't fully documented and aren't always masked properly. The
comment about the bits in readfat() will be removed when the masking
is fixed.

Submitted by: rnordier

Prepare to fix checkdirty() by moving it from check.c to fat.c. It is
identical to a subset of readfat(), so it belongs near readfat() if not
in it.

Forced commit to note that my previous commit was a Darwin merge.

s/filesystem/file system/g as discussed on -developers

o __P removed
o ansi function prototypes
o unifdef -D__STDC__
o __dead2 on usage prototype
o remove now-bogus main prototype

Add fsck_msdosfs.

Obtained from: NetBSD