MFC of 213119

MFC of 213119

Reported problem:
Large (60GB) filesystems created using "newfs -U -O 1 -b 65536 -f 8192"
show incorrect results from "df" for free and used space when mounted
immediately after creation. fsck on the new filesystem (before ever
mounting it once) gives a "SUMMARY INFORMATION BAD" error in phase 5.

This error hasn't occurred in any runs of fsck immediately after
"newfs -U -b 65536 -f 8192" (leaving out the "-O 1" option).

Solution:
The default UFS1 superblock is located at offset 8K in the filesystem
partition; the default UFS2 superblock is located at offset 64K in
the filesystem partition. For UFS1 filesystems with a blocksize of
64K, the first alternate superblock resides at 64K which is the the
location used for the default UFS2 superblock. By default, the
system first checks for a valid superblock at the default location
for a UFS2 filoesystem. For a UFS1 filesystem with a blocksize of
64K, there is a valid UFS1 superblock at this location. Thus, even
though it is expected to be a backup superblock, the system will
use it as its default superblock. So, we have to ensure that all the
statistcs on usage are correct in this first alternate superblock
as it is the superblock that will actually be used.

While tracking down this problem, another limitation of UFS1 became
evident. For UFS1, the number of inodes per cylinder group is stored
in an int16_t. Thus the maximum number of inodes per cylinder group
is limited to 2^15 - 1. This limit can easily be exceeded for block
sizes of 32K and above. Thus when building UFS1 filesystems, newfs
must limit the number of inodes per cylinder group to 2^15 - 1.

Reported by: Guy Helmer<ghelmer@palisadesys.com>
Followup by: Bruce Cran <brucec@freebsd.org>
PR: 107692

git-svn-id: svn://svn.freebsd.org/base/stable/8@215728 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f