xfs_db: use inode cluster buffers for inode IO

xfs_db: use inode cluster buffers for inode IO

When we mount the filesystem inside xfs_db, libxfs is tasked with
reading some information from disk, such as root inodes. Because
libxfs does this inode reading, it uses inode cluster buffers to
read the inodes. xfs_db, OTOH, just uses FSB sized buffers to read
inodes, and hence xfs_db throws a warning when reading the root
inode block like so:

$ sudo xfs_db -c "sb 0" -c "p rootino" -c "inode 32" /dev/vda
Version 5 superblock detected. xfsprogs has EXPERIMENTAL support enabled!
Use of these features is at your own risk!
rootino = 32
7f59f20e6740: Badness in key lookup (length)
bp=(bno 0x20, len 8192 bytes) key=(bno 0x20, len 1024 bytes)
$

There is another way this can happen, and that is dumping raw data
from disk using either the "fsb NNN" or "daddr MMM" commands to dump
untyped information. This is always read in sector or filesystem
block units, and so will cause similar badness warnings.

To avoid this problem when reading inodes, teach xfs_db to read
inode clusters rather individual filesystem blocks when asked to
read an inode.

Signed-off-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Rich Johnston <rjohnston@sgi.com>