mkuzip: drop support for executable uzip images

A uzip image has a 128-byte header, historically, this header could be
executed as a shell script to mount the uzip image to a user provided
mountpoin

mkuzip: drop support for executable uzip images

A uzip image has a 128-byte header, historically, this header could be
executed as a shell script to mount the uzip image to a user provided
mountpoint.

The embedded shell commands only work for uzip images that were created
with zlib or zstd compression that contained an ISO-9660 file system.
Given the limited space available in the uzip header, it is not
practical to extend this feature to include other file systems or to
provide sensible error handling and error messages to the user.
For these reasons, abandon the embedded shell script in the uzip image
header.

To maintain backwards compatibility, the shebang and shell must reside
in the 128-byte header.

This change of behavior is documented in mkuzip(8) and an example
has been provided for creating/mounting uzip images.

PR: 276174

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Remove $FreeBSD$: two-line .h pattern

Remove /^\s*\*\n \*\s+\$FreeBSD\$$\n/

spdx: The BSD-2-Clause-FreeBSD identifier is obsolete, drop -FreeBSD

The SPDX folks have obsoleted the BSD-2-Clause-FreeBSD identifier. Catch
up to that fact and revert to their recommended match of

spdx: The BSD-2-Clause-FreeBSD identifier is obsolete, drop -FreeBSD

The SPDX folks have obsoleted the BSD-2-Clause-FreeBSD identifier. Catch
up to that fact and revert to their recommended match of BSD-2-Clause.

Discussed with: pfg
MFC After: 3 days
Sponsored by: Netflix

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geom_uzip(4), mkuzip(8): Add Zstd image mode

The Zstd format bumps the CLOOP major number to 4 to avoid incompatibility
with older systems. Support in geom_uzip(4) is conditional on the ZSTDIO
kern

geom_uzip(4), mkuzip(8): Add Zstd image mode

The Zstd format bumps the CLOOP major number to 4 to avoid incompatibility
with older systems. Support in geom_uzip(4) is conditional on the ZSTDIO
kernel option, which is enabled in amd64 GENERIC, but not all in-tree
configurations.

mkuzip(8) was modified slightly to always initialize the nblocks + 1'th
offset in the CLOOP file format. Previously, it was only initialized in the
case where the final compressed block happened to be unaligned w.r.t.
DEV_BSIZE. The "Fake" last+1 block change in r298619 means that the final
compressed block's 'blen' was never correct unless the compressed uzip image
happened to be BSIZE-aligned. This happened in about 1 out of every 512
cases. The zlib and lzma decompressors are probably tolerant of extra trash
following the frame they were told to decode, but Zstd complains that the
input size is incorrect.

Correspondingly, geom_uzip(4) was modified slightly to avoid trashing the
nblocks + 1'th offset when it is known to be initialized to a good value.
This corrects the calculated final real cluster compressed length to match
that printed by mkuzip(8).

mkuzip(8) was refactored somewhat to reduce code duplication and increase
ease of adding other compression formats.

* Input block size validation was pulled out of individual compression
init routines into main().

* Init routines now validate a user-provided compression level or select
an algorithm-specific default, if none was provided.

* A new interface for calculating the maximal compressed size of an
incompressible input block was added for each driver. The generic code
uses it to validate against MAXPHYS as well as to allocate compression
result buffers in the generic code.

* Algorithm selection is now driven by a table lookup, to increase ease of
adding other formats in the future.

mkuzip(8) gained the ability to explicitly specify a compression level with
'-C'. The prior defaults -- 9 for zlib and 6 for lzma -- are maintained.
The new zstd default is 9, to match zlib.

Rather than select lzma or zlib with '-L' or its absense, respectively, a
new argument '-A <algorithm>' is provided to select 'zlib', 'lzma', or
'zstd'. '-L' is considered deprecated, but will probably never be removed.

All of the new features were documented in mkuzip.8; the page was also
cleaned up slightly.

Relnotes: yes

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