eefd8f96fb
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
264 lines
7.2 KiB
Groff
264 lines
7.2 KiB
Groff
.\"-
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.\" Copyright (c) 2004-2016 Maxim Sobolev <sobomax@FreeBSD.org>
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.\" All rights reserved.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
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.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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.\" ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
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.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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.\" SUCH DAMAGE.
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.\"
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.\" $FreeBSD$
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.\"
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.Dd August 9, 2019
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.Dt MKUZIP 8
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.Os
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.Sh NAME
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.Nm mkuzip
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.Nd compress disk image for use with
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.Xr geom_uzip 4
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class
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.Sh SYNOPSIS
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.Nm
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.Op Fl dSsvZ
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.Op Fl A Ar compression_algorithm
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.Op Fl C Ar compression_level
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.Op Fl j Ar compression_jobs
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.Op Fl o Ar outfile
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.Op Fl s Ar cluster_size
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.Ar infile
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.Sh DESCRIPTION
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The
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.Nm
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utility compresses a disk image file so that the
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.Xr geom_uzip 4
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class will be able to decompress the resulting image at run-time.
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This allows for a significant reduction of size of disk image at
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the expense of some CPU time required to decompress the data each
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time it is read.
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The
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.Nm
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utility
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works in two phases:
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.Bl -enum
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.It
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An
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.Ar infile
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image is split into clusters; each cluster is compressed.
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.It
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The resulting set of compressed clusters is written to the output file.
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In addition, a
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.Dq table of contents
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header is written which allows for efficient seeking.
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.El
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.Pp
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The options are:
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.Bl -tag -width indent
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.It Fl A Op Ar lzma | Ar zlib | Ar zstd
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Select a specific compression algorithm.
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If this option is not provided, the default is
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.Ar zlib .
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.Pp
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The
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.Ar lzma
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algorithm provides noticeable better compression levels than zlib on the same
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data set.
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It has vastly slower compression speed and moderately slower decompression
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speed.
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.Pp
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The
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.Ar zstd
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algorithm provides better compression levels than zlib on the same data set.
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It also has faster compression and decompression speed than zlib.
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In the very high compression
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.Dq level
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settings, it does not offer quite as high a compression ratio as
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.Ar lzma .
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However, its decompression speed does not suffer at high compression
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.Dq levels .
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.It Fl C Ar compression_level
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Select the integer compression level used to parameterize the chosen
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compression algorithm.
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.Pp
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For any given algorithm, a lesser number selects a faster compression mode.
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A greater number selects a slower compression mode.
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Typically, for the same algorithm, a greater
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.Ar compression_level
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provides better final compression ratio.
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.Pp
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For
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.Ar lzma ,
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the range of valid compression levels is
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.Va 0-9 .
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The
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.Nm
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default for lzma is
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.Va 6 .
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.Pp
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For
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.Ar zlib ,
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the range of valid compression levels is
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.Va 1-9 .
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The
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.Nm
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default for zlib is
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.Va 9 .
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.Pp
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For
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.Ar zstd ,
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the range of valid compression levels is currently
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.Va 1-19 .
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The
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.Nm
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default for zstd is
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.Va 9 .
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.It Fl d
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Enable de-duplication.
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When the option is enabled
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.Nm
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detects identical blocks in the input and replaces each subsequent occurrence
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of such block with pointer to the very first one in the output.
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Setting this option results is moderate decrease of compressed image size,
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typically around 3-5% of a final size of the compressed image.
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.It Fl j Ar compression_jobs
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Specify the number of compression jobs that
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.Nm
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runs in parallel to speed up compression.
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When option is not specified the number of jobs set to be equal
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to the value of
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.Va hw.ncpu
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.Xr sysctl 8
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variable.
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.It Op Fl L
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Legacy flag that indicates the same thing as
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.Dq Fl A Ar lzma .
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.It Fl o Ar outfile
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Name of the output file
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.Ar outfile .
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The default is to use the input name with the suffix
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.Pa .uzip
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for the
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.Xr zlib 3
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compression or
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.Pa .ulzma
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for the
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.Xr lzma 3 .
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.It Fl S
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Print summary about the compression ratio as well as output
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file size after file has been processed.
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.It Fl s Ar cluster_size
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Split the image into clusters of
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.Ar cluster_size
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bytes, 16384 bytes by default.
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The
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.Ar cluster_size
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should be a multiple of 512 bytes.
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.It Fl v
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Display verbose messages.
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.It Fl Z
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Disable zero-block detection and elimination.
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When this option is set,
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.Nm
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compresses blocks of zero bytes just as it would any other block.
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When the option is not set,
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.Nm
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detects and compresses zero blocks in a space-efficient way.
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Setting
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.Fl Z
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increases compressed image sizes slightly, typically less than 0.1%.
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.El
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.Sh IMPLEMENTATION NOTES
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The compression ratio largely depends on the compression algorithm, level, and
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cluster size used.
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For large cluster sizes (16kB and higher), typical overall image compression
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ratios with
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.Xr zlib 3
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are only 1-2% less than those achieved with
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.Xr gzip 1
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over the entire image.
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However, it should be kept in mind that larger cluster sizes lead to higher
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overhead in the
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.Xr geom_uzip 4
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class, as the class has to decompress the whole cluster even if
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only a few bytes from that cluster have to be read.
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.Pp
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Additionally, the threshold at 16-32 kB where a larger cluster size does not
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benefit overall compression ratio is an artifact of the
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.Xr zlib 3
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algorithm in particular.
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.Ar Lzma
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and
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.Ar Zstd will continue to provide better compression ratios as cluster sizes
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are increased, at high enough compression levels.
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The same tradeoff continues to apply: reads in
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.Xr geom_uzip 4
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become more expensive the greater the cluster size.
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.Pp
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The
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.Nm
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utility
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inserts a short shell script at the beginning of the generated image,
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which makes it possible to
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.Dq run
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the image just like any other shell script.
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The script tries to load the
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.Xr geom_uzip 4
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class if it is not loaded, configure the image as an
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.Xr md 4
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disk device using
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.Xr mdconfig 8 ,
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and automatically mount it using
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.Xr mount_cd9660 8
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on the mount point provided as the first argument to the script.
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.Pp
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The de-duplication is a
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.Fx
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specific feature and while it does not require any changes to on-disk
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compressed image format, however it did require some matching changes to the
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.Xr geom_uzip 4
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to handle resulting images correctly.
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.Pp
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To make use of
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.Ar zstd
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.Nm
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images, the kernel must be configured with
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.Cd ZSTDIO .
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It is enabled by default in many
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.Cd GENERIC
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kernels provided as binary distributions by
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.Fx .
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The status on any particular system can be verified by checking
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.Xr sysctl 8
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.Dv kern.features.geom_uzip_zstd
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for
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.Dq 1 .
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.Sh EXIT STATUS
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.Ex -std
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.Sh SEE ALSO
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.Xr gzip 1 ,
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.Xr xz 1 ,
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.Xr zstd 1 ,
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.Xr zlib 3 ,
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.Xr geom 4 ,
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.Xr geom_uzip 4 ,
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.Xr md 4 ,
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.Xr mdconfig 8 ,
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.Xr mount_cd9660 8
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.Sh AUTHORS
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.An Maxim Sobolev Aq Mt sobomax@FreeBSD.org
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