.\" This manpage has been automatically generated by docbook2man
.\" from a DocBook document. This tool can be found at:
.\"
.\" Please send any bug reports, improvements, comments, patches,
.\" etc. to Steve Cheng .
.TH "CREATE_COMPRESSED_FS" "1" "04 Dezember 2006" "" ""
.SH NAME
create_compressed_fs, extract_compressed_fs \- convert and extract a filesystem to/from a cloop volume
.SH SYNOPSIS
\fBcreate_compressed_fs\fR [ \fBOPTIONS\fR ] \fBimage\fR \fBoutfile\fR
\fBextract_compressed_fs\fR \fBfilename\fR
.SH "DESCRIPTION"
.PP
\fBcreate_compressed_fs\fR compresses a filesystem image
to a compressed image suitable for mounting with the cloop driver.
.PP
\fBextract_compressed_fs\fR uncompresses a filesystem image
created by create_compressed_fs.
.SH "OPTIONS"
.PP
Run the \fBcreate_compressed_fs\fR
command with "-h" to get a list of available options and description of data
storages modes and advanced usage (eg. with a network cluster). Blocksize
must be a multiple of 512 bytes.
.PP
There is an alternative set of options which is supported for
compatibility with the original version of create_compressed_fs. When
it's called with a pure number as output, it assumes the old syntax and
maps the default options to memory mode and the block size to the
number. -b for best mode is recognized as well.
.SH "EXAMPLES"
.PP
create_compressed_fs image.ext2 image.ext2.cloop
.PP
extract_compressed_fs image.ext2.cloop | cmp image.ext2 -
.PP
mkcmd="genisoimage -joliet-long -D -r data"
.PP
$mkcmd | create_compressed_fs -s $($mkcmd --print-size)i - file.cloop
.PP
create_compressed_fs image.iso -S image.cloop.a0 - | split -b 1024m - image.cloop.
.PP
cat image.cloop.* | cdrskin -
.SH "NOTES"
.PP
For optimal performance, create_compressed_fs should be used with real
input and output files.
.PP
Operation with STDIN or STDOUT is complicated. create_compressed_fs
cannot operate as a simple pipe filter because it needs to know some
things in advance: a) the data length, b) the block lengths calculated
during the compression. This meta data needs to be stored in the header
AFTER the compression is trough, therefore it is not possible to push
all generated data to STDOUT on-the-fly.
.PP
And so compromises need to be made. The simpliest method (used by the
ancient create_compressed_fs) is a big temporary memory buffer (option
\fB-m\fR) to keep compressed data in RAM. However, the
overall system performance suffers from such usage and this may drive
other applications into OOM conditions.
.PP
The next alternative to this is storing the temprorary data in an extra
file aside (the \fB-f\fR option). This improves the overall
system performance but create_compressed_fs operation is slower because
it needs to copy data back when it's finished. Plus, double disk space
for the output is required. If disk space is limited, the
\fB-r\fR option could be used (reusing output file for
temporary data), however the speed of the copy-back step may decrease
significantly.
.PP
There are strategies to avoid the temporary data storage completely.
First, only files should be used. If that is not possible, then the
output should be a (seekable) file and the input data length should be
known (either specified with the \fB-s\fR option or detected from the input
file size).
.PP
Second, it is possible to store the header of the cloop volume in a
separate file. After the work, header can be merged together with the
compressed data with the cat command. The output data can be written to
stdout. Since the header is stored too late, this method is not very
usefull for immediate data transfer. However, it allows to do some
tricks like piping to the split utility (to store DVD images in smaller
files on VFAT) or piping data trough ssh if the local system has no
disk space (and copying the header separately).
.SH "MOUNTING"
.PP
You can pass an option to the cloop module on loading, or use losetup or losetup functionality of the mount command. Examples:
.PP
insmod cloop.o file=/path/to/compressed/image
.PP
losetup /dev/cloop1 /path/to/compressed/image
.PP
mount -o ro -t whatever /dev/cloop /mnt/compressed
.PP
mount cl /mnt/misc -oloop=/dev/cloop0
.SH "SEE ALSO"
.PP
\fB/usr/share/doc/cloop-utils/*\fR, \fB/usr/share/doc/cloop-src/*\fR
.SH "AUTHOR"
.PP
This manual page was written by Eduard Bloch
for the Debian
GNU/Linux system (but may be used by others). Permission is
granted to copy, distribute and/or modify this document under the terms of
the GNU GPLv2.