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SquashFS with LZMA compression

萧渝
2023-12-01

SquashFS (.sfs) is a compressed read-only file system for Linux. SquashFS compresses files, inodes and directories, and supports block sizes up to 1 MB for greater compression. SquashFS is also free software (licensed under the GPL) for accessing SquashFS filesystems.

SquashFS is intended for general read-only file system use and in constrained block device/memory systems (e.g. embedded systems) where low overhead is needed. The standard version of SquashFS uses gzip compression.

Here is my How-To on how to get LZMA compressed SquashFS in Archlinux.

Requirements
1) squashfs-tools
 with LZMA patches. This package provides tools (mksquashfs, unsquashfs) to create Squashfs filesystem. With standard version (from /extra repository) you can create only gzip-compressed  Squashfs filesystem. To get LZMA support you must install package:
squashfs-tools-lzma
This package doesn't conflict with package from /extra. It provides mksquashfs.lzma, unsquashfs.lzma. So if you want create LZMA compressed filesystem you must use:

mksquashfs.lzma source dest

Otherwise for GZIP compressed filesystem:

mksquashfs source dest

2) squashfs module with LZMA patches. Without it you cant't mount your LZMA compressed filesystems. Here is two ways on how to get it.
2.1 Patch kernel with SquashFS LZMA patches.
Before proceed i recommend to read Custom Kernel Compilation with ABS
You must apply on sources three patches:
051-squashfs_pcomp.patch
052-pcomp_lzma_support.patch
053-squashfs_lzma.patch
And set in kernel config:

CONFIG_SQUASHFS=m|y
CONFIG_SQUASHFS_SUPPORT_ZLIB=y
CONFIG_SQUASHFS_SUPPORT_LZMA=y
CONFIG_CRYPTO_UNLZMA=m|y

m|y means that you can build it as a module (m) or as a part of kernel (y).
Build kernel as usual and after that you can mount LZMA compressed filesystems.

2.2 Build standalone module without patching and rebuilding the whole kernel. 
Warning. I am not Linux guru. And i think that this method is not optimal (but it works). Any suggestions are welcome from experienced users.
For ARCH kernel here is PKGBUILD on AUR:
kernel26-squashfs-lzma-modules

Create directory (called for example squashfs-module) somewhere on your hard disk. Cd to that directory;
Download here Linux kernel sources (i strongly recommend to use same sources as in PKGBUILD of your kernel);
Download LZMA patches listed in 2.1;
Now you need kernel config file. Get it from your kernel package;
Unpack linux kernel sources. Cd to that directory;
Copy kernel config file here and rename it to .config;
Now we can patch our kernel:
  patch -Np1 -i /pathto_051-squashfs_pcomp.patch
  patch -Np1 -i /pathto_052-pcomp_lzma_support.patch
  patch -Np1 -i /pathto_053-squashfs_lzma.patch
Before building modules we need some preparations:
  make prepare
  make modules_prepare
The kernel is patched and all preparations are ready. We can build modules:
  make modules SUBDIRS=crypto
  make modules SUBDIRS=fs/squashfs
Modules are ready. Now we need to copy it to our kernel modules directory:
  cp crypto/unlzma.ko /lib/modules/KERNELVERSION/misc
  cp fs/squashfs/squashfs.ko /lib/modules/KERNELVERSION/misc/squashfs_lzma.ko
Now execute:
  depmod KERNELVERSION
Modules are installed and ready for use.

Now you can load modules:

modprobe unlzma
modprobe squashfs_lzma

Remember to load both of them (unlzma and squashfs_lzma) and in that order.

I don't like this way. I think it is to possible to simplify this process. And this modules doesn't contain information about dependency. So you must manually load unlzma module.

How to use it
1)
 First we need to create SquashFS filesystem.
For GZIP:

mksquashfs source dest

For LZMA:

mksquashfs.lzma source dest

For example:

sudo mksquashfs.lzma /usr /usr.sqfs

2) Now we can mount it as usual.

sudo mount -t squashfs -o loop /usr.sqfs /mountpoint

Benchmark

du -hs /usr/
3.3G    /usr/

GZIP (standard):

sudo mksquashfs /usr/ /usr.sqfs
Parallel mksquashfs: Using 2 processors                
Creating 4.0 filesystem on /usr.sqfs, block size 131072.
[=============================\] 137140/137140 100%
Exportable Squashfs 4.0 filesystem, data block size 131072                                                            
        compressed data, compressed metadata, compressed fragments                                                    
        duplicates are removed                                                                                        
Filesystem size 1449060.58 Kbytes (1415.10 Mbytes)                                                                    
        46.41% of uncompressed filesystem size (3122543.79 Kbytes)                                                    
Inode table size 1365724 bytes (1333.71 Kbytes)                                                                       
        29.28% of uncompressed inode table size (4664165 bytes)                                                       
Directory table size 1437349 bytes (1403.66 Kbytes)                                                                   
        42.30% of uncompressed directory table size (3397611 bytes)                                                   
Number of duplicate files found 21775                                                                                 
Number of inodes 141741                                                                                               
Number of files 127438                                                                                                
Number of fragments 7820                                                                                              
Number of symbolic links  3853                                                                                        
Number of device nodes 0                                                                                              
Number of fifo nodes 0                                                                                                
Number of socket nodes 0                                                                                              
Number of directories 10450                                                                                           
Number of ids (unique uids + gids) 6                                                                                  
Number of uids 2                                                                                                      
        root (0)                                                                                                      
        policykit (102)                                                                                               
Number of gids 6                                                                                                      
        root (0)                                                                                                      
        locate (21)                                                                                                   
        mail (12)                                                                                                     
        tty (5)                                                                                                       
        policykit (102)                                                                                               
        dbus (81)                                                                                                     

real    7m28.167s
user    11m18.825s
sys     0m4.214s
du -h /usr.sqfs
1.4G    /usr.sqfs

LZMA (patched):

sudo mksquashfs.lzma /usr/ /usr.lzma.sqfs
Parallel mksquashfs: Using 2 processors                            
Creating 4.0 filesystem on /usr.lzma.sqfs, block size 131072.      
[=============================|] 137140/137140 100%
Exportable Squashfs 4.0 filesystem, data block size 131072                                                            
        compressed data, compressed metadata, compressed fragments                                                    
        duplicates are removed
Filesystem size 1326846.64 Kbytes (1295.75 Mbytes)
        42.49% of uncompressed filesystem size (3122543.79 Kbytes)
Inode table size 1067747 bytes (1042.72 Kbytes)
        22.89% of uncompressed inode table size (4664165 bytes)
Directory table size 1360891 bytes (1329.00 Kbytes)
        40.05% of uncompressed directory table size (3397611 bytes)
Number of duplicate files found 21775
Number of inodes 141741
Number of files 127438
Number of fragments 7820
Number of symbolic links  3853
Number of device nodes 0
Number of fifo nodes 0
Number of socket nodes 0
Number of directories 10450
Number of ids (unique uids + gids) 6
Number of uids 2
        root (0)
        policykit (102)
Number of gids 6
        root (0)
        locate (21)
        mail (12)
        tty (5)
        policykit (102)
        dbus (81)

real    22m51.122s
user    28m39.617s
sys     9m46.870s
du -h /usr.lzma.sqfs
1.3G    /usr.lzma.sqfs

Results
Size of /usr:
 3.1 Gib (3.327.028.002) 131.201 files, 10.642 sub-folders
Size of usr.sqfs: 1.4 Gib (1.483.841.536)
Size of usr.lzma.sqfs: 1.3 GiB (1.358.692.352)

P.s. Sorry for my poor english. Any corrections are welcome.
P.p.s. Any suggestions, improvements are welcome.


from:https://bbs.archlinux.org/viewtopic.php?id=83720

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