Copy head (r256279) to stable/10 as part of the 10.0-RELEASE cycle.

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

Fix problem with geom_label(4) not recognizing UFS labels on filesystems
extended using growfs(8). The problem here is that geom_label checks if
the filesystem size recorded in UFS superblock is equal to the provider
(i.e. device) size. This check cannot be removed due to backward
compatibility. On the other hand, in most cases growfs(8) cannot set
fs_size in the superblock to match the provider size, because, differently
from newfs(8), it cannot recompute cylinder group sizes.

To fix this problem, add another superblock field, fs_providersize, used
only for this purpose. The geom_label(4) will attach if either fs_size
(filesystem created with newfs(8)) or fs_providersize (filesystem expanded
using growfs(8)) matches the device size.

PR: kern/165962
Reviewed by: mckusick
Sponsored by: FreeBSD Foundation

Revert r235918 for now and add comment explaining the reason for the
size check.

Make g_label(4) ignore provider size when looking for UFS labels.
Without it, it fails to create labels for filesystems resized by
growfs(8).

PR: kern/165962
Submitted by: Olivier Cochard-Labbe <olivier at cochard dot me>

Provide a set of sysctls and tunables to disable device node creation
for specific "kinds" of disk labels - for example, GPT UUIDs. Reason
for this is that sometimes, other GEOM classes attach to these device
nodes instead of the proper ones - e.g. they attach to /dev/gptid/XXX
instead of /dev/ada0p2, which is annoying.

Reviewed by: pjd (earlier version)
MFC after: 1 month

Create GEOM labels from UFS IDs, e.g. /dev/ufsid/49c97b1faa2adc43. UFS IDs
are always present and can be used to identify file systems (useful if
hardware devices move often).

Actually-by: pjd
Approved by: gnn (mentor)

Fix detecting of UFS1 label when mediasize%fragsize != 0.

Submitted by: Stanislav Sedov
PR: kern/84637
MFC after: 1 week

We need to check if file system size is equal to provider's size, because
sysinstall(8) still bogusly puts first partition at offset 0 instead of 16,
so glabel/ufs will find file system on slice instead of partition.

Before sysinstall is fixed, we must keep this code, which means that we
wont't be able to detect UFS file systems created with 'newfs -s ...'.

PS. bsdlabel(8) creates partitions properly.

MFC after: 3 days

- Do not depend on fact that file system covers entire provider.
It won't work for file systems created with -s option.
Use better file system verfication.
- Add myself to the copyright.

MFC after: 3 days

This function returns nothing.

If provider's sector size prevents reading SBLOCKSIZE bytes return
immediatelly.

Remove trailing spaces.

Don't pass error value pointer to g_read_data(9) at all if we don't
have any use of it.

Suggested by: pjd

Check for g_read_data(9) errors properly:

o The only indication of error condition is NULL value returned by
the function;

o value pointed to by error argument is undefined in the case when
operation completes successfully.

Discussed with: phk

The size of a filesystem may be less than the size of the provider it
resides on. Fix the special case of the filesystem fragment size not
evenly dividing the size of the provider. Fixing the general case
probably requires better superblock validation (left as an exercise to
the reader).

merge from geom_vol_ffs.c rev 1.14 (avoid unaligned I/O requests)

Introduce GEOM_LABEL class.
This class is used for detecting volume labels on file systems:
UFS, MSDOSFS (FAT12, FAT16, FAT32) and ISO9660.
It also provide native labelization (there is no need for file system).

g_label_ufs.c is based on geom_vol_ffs from Gordon Tetlow.
g_label_msdos.c and g_label_iso9660.c are probably hacks, I just found
where volume labels are stored and I use those offsets here,
but with this class it should be easy to do it as it should be done by
someone who know how.
Implementing volume labels detection for other file systems also should
be trivial.

New providers are created in those directories:
/dev/ufs/ (UFS1, UFS2)
/dev/msdosfs/ (FAT12, FAT16, FAT32)
/dev/iso9660/ (ISO9660)
/dev/label/ (native labels, configured with glabel(8))

Manual page cleanups and some comments inside were submitted by
Simon L. Nielsen, who was, as always, very helpful. Thanks!