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
o Split the compression across several worker threads. By default, "several"
matches number of CPUs, capped at 24 for sanity when running on a very big
hardwares. Provide option to set that number manually;
o Fix bug inherited from the mkulzma (R.I.P) which degraded already slow LZMA
compression even further by calling function to release compression state
after processing each block.
It is neither documented as required nor actually required by the LZMA
library. This caused spree of system calls to release memory and then map
it again for every block. LZMA compression is more than 2x faster after this
change alone;
o Record time it takes to do compression and report throughput achieved.
o Add simple first-level 256 entry hash table for de-dup code, so it's not
becoming a bottleneck at big files.
and geom_uncompress(4):
1. mkuzip(8):
- Proper support for eliminating all-zero blocks when compressing an
image. This feature is already supported by the geom_uzip(4) module
and CLOOP format in general, so it's just a matter of making mkuzip(8)
match. It should be noted, however that this feature while it sounds
great, results in very slight improvement in the overall compression
ratio, since compressing default 16k all-zero block produces only 39
bytes compressed output block, which is 99.8% compression ratio. With
typical average compression ratio of amd64 binaries and data being
around 60-70% the difference between 99.8% and 100.0% is not that
great further diluted by the ratio of number of zero blocks in the
uncompressed image to the overall number of blocks being less than
0.5 (typically). However, this may be important from performance
standpoint, so that kernel are not spinning its wheels decompressing
those empty blocks every time this zero region is read. It could also
be important when you create huge image mostly filled with zero
blocks for testing purposes.
- New feature allowing to de-duplicate output image. It turns out that
if you twist CLOOP format a bit you can do that as well. And unlike
zero-blocks elimination, this gives a noticeable improvement in the
overall compression ratio, reducing output image by something like
3-4% on my test UFS2 3GB image consisting of full FreeBSD base system
plus some of the packages (openjdk, apache etc), about 2.3GB worth of
file data (800+MB compressed). The only caveat is that images created
with this feature "on" would not work on older versions of FeeBSDxi
kernel, hence it's turned off by default.
- provide options to control both features and document them in manual
page.
- merge in all relevant LZMA compression support from the mkulzma(8),
add new option to select between both.
- switch license from ad-hoc beerware into standard 2-clause BSD.
2. geom_uzip(4):
- implement support for de-duplicated images;
- optimize some code paths to handle "all-zero" blocks without reading
any compressed data;
- beef up manual page to explain that geom_uzip(4) is not limited only
to md(4) images. The compressed data can be written to the block
device and accessed directly via magic of GEOM(4) and devfs(4),
including to mount root fs from a compressed drive.
- convert debug log code from being compiled in conditionally into
being present all the time and provide two sysctls to turn it on or
off. Due to intended use of the module, it can be used in
environments where there may not be a luxury to put new kernel with
debug code enabled. Having those options handy allows debug issues
without as much problem by just having access to serial console or
network shell access to a box/appliance. The resulting additional
CPU cycles are just few int comparisons and branches, and those are
minuscule when compared to data decompression which is the main
feature of the module.
- hopefully improve robustness and resiliency of the geom_uzip(4) by
performing some of the data validation / range checking on the TOC
entries and rejecting to attach to an image if those checks fail.
- merge in all relevant LZMA decompression support from the
geom_uncompress(4), enable automatically when appropriate format is
indicated in the header.
- move compilation work into its own worker thread so that it does not
clog g_up. This allows multiple instances work in parallel utilizing
smp cores.
- document new knobs in the manual page.
Reviewed by: adrian
MFC after: 1 month
Differential Revision: https://reviews.freebsd.org/D5333
geom_uzip module. This is based on utility I wrote some 3 years ago for a
hack for md(4), which functionally was close to what geom_uzip does today.
Since I don't have a time to test that it compiles/works on other arches,
stick it to i386 only. Will do it later.
Unlike original cloop util, this one embedds FreeBSD-compatible shell code
into the generated image, not Linux one. Unfortunately severe space
restriction imposed by the CLOOP format doesn't allow to put conditional
code which will work both on Linux and FreeBSD. In fact it was quite a
challenge to fit necessary FreeBSD code into 127 bytes. ;-)
