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)

Bail out when memory allocation is failed, rather than referencing
a NULL pointer.

PR: kern/94480
Submitted by: Michiel Pelt <m.pelt xs4all nl>

Add a berase() function which uses ioctl(DIOCGDELETE) to erase a slab
of the disk.

Add XXX'ed temporary bounce-buffering.

Reduce diffs with code in Perforce:
Parenthesise return values.

MFp4: Fix copy&paste English error.

Clean up error reporting in block.c, so that it gives honest error strings
for the sorts of errors we run into[1]. This also gives us room to put in a
vaguely appropriate casts to silence warnings since our compiler doesn't like
when we compare ssize_t to size_t[2]. Add a cast in sblock.c[3] to silence
a warning because of signed vs. size_t hell (again). Clean up nearby
excessive parenthemutilation[4].

Reviewed by: bde [2] [3]
Suggested by: bde, many [1]
Submitted by: bde [4]

An aside about [4], bde notes that we do not check for a negative value for
the fs bsize. I'm nto going to do that in every situation we use it, one must
expect a reasonable program to pass down reasonable values. Some foot shooting
protection I will tolerate, some I will not. Also he suggests some possible
conditional improvements there, which I may take to heart.

PS: For me at least, this is now WARNS=5 clean...

API for opening (and tracking) writable file descriptors per disk.

bwrite, not sbwrite, needs to open for writing and write.

Don't crash when utilities are dumb and try to read less than the disk block
size (dumpfs may try to read the cylinder size (or is is sector size?) by way
of bread). Prevents a bounds error.

Nuke dumb error reporting code, people can just use disk::d_error. Unify the
DEBUG and d_error initialisation into an ERROR macro, which can both trace and
set the d_error field. Much a more meaningful thing, I should say.

Add the concept of a per-disk error string, and a function which prints it
along with the errno, if one is set.

Add libufs, a library for dealing with UFS filesystems from userland to
the build. It is here to compartmentalise functionality currently duplicated
in many notable programs in the base system. It currently handles block
reads and writes, as well as reading and writing of the filesystem superblock,
and the reading/lookup of inode data. It supports both UFS and UFS2. I
will be maintaining it, and porting programs to use it, however for now, it
is simply being built as part of world.