Long ago, bread() set b_blkno to the disk block number as a side effect
of doing physical i/o (or it just retained the setting from when the
i/o was done). The setting is lost when buffers go away and then are
reconsituted from VM. bread() originally compensated by doing a
VOP_BMAP() to recover b_blkno, but this was no good since it sometimes
caused extra i/o or even deadlock for bread()ing metadata to do the
bmap. This was fixed in vfs_bio.c 1.33 (1995/03/03) and ffs_balloc.c
1.5, etc., by removing the VOP_BMAP() from bread() and breadn(), and
changing all (?) places that used b_blkno to set it if necessary.
ext2fs was not imported until later in 1995 and was still depending on
the old behaviour of bread() in at least ext2_balloc(). This caused
filesystem and file corruption by clobbering direct block numbers in
inodes.
<sys/bio.h>.
<sys/bio.h> is now a prerequisite for <sys/buf.h> but it shall
not be made a nested include according to bdes teachings on the
subject of nested includes.
Diskdrivers and similar stuff below specfs::strategy() should no
longer need to include <sys/buf.> unless they need caching of data.
Still a few bogus uses of struct buf to track down.
Repocopy by: peter
file for GPL restrictions. This code was ported to the BSD platform
by Godmar Back <gback@facility.cs.utah.edu> and specifically to FreeBSD
by John Dyson. This code is still green and should be used with caution.
Additional changes to UFS necessary to make this code work will be commited
seperately.
Submitted by: Godmar Back <gback@facility.cs.utah.edu>
Obtained from: Lites/Mach4
