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smashfs

smashfs is a read-only linux kernel filesystem with compression support.

  1. overview
  2. creating
  3. extracting
  4. linux kernel
  5. using
  6. contact

1. overview

smashfs is a read-only compressed filesystem for linux kernel.

supported compressions are:

  • none
  • gzip
  • lzma
  • lzo
  • xz

a smashed filesystem has four main blocks

  • super block

    stored as uncompressed, and holds the information about the filesystem.

  • nodes table

    stored as compressed, and hold the information about filesystem items.

  • blocks table

    stored as compressed, and holds the information about accessing data blocks.

  • data blocks

    stored as compressed, and holds the actual data of filesystem items.

2. creating

a smashed filesystem is created with the tool mkfs.smashfs.

creating a smashed filesystem from source directory with:

# mkfs.smashfs -s source_directory -o smashfs.fs -b 131072 -c xz -j 8 -d

command line options:

  • -s / --source

    source file or directory

  • -o / --output

    output file

  • -b / --block_size

    data block size, default is 1048576 bytes

  • -d / --debug

    enable debugging, can be used repeatedly to increase debug level

  • -j / --jobs

    enable and set job count for multi-threaded compressing to decrease filesystem creation time, default is 8

  • -c / --compressor

    select compression library, default is none

  • --no_group_mode

    disable group mode and use user mode to gain some space

  • --no_other_mode

    disable other mode and use user mode to gain some space

  • --no_uid

    disable uid and use 0 to gain some space

  • --no_gid

    disable gui and use 0 to gain some space

  • --no_ctime

    disable ctime and use filesystem creation time to gain some space

  • --no_mtime

    disable mtime and use filesystem creation time to gain some space

  • --no_padding

    disable padding to 4K to gain some space

  • --no_duplicates

    disable duplicate file checking, will increase filesystem size. may be usefull for debugging purposes.

3. extracting

a smashed filesystem is extracted with the tool unfs.smashfs.

extracting a smashed filesystem to output directory with:

# unfs.smashfs -s smashfs.fs -o output_directory -d

command line options:

  • -s / --source

    source file or directory

  • -o / --output

    output file

  • -d / --debug

    enable debugging, can be used repeatedly to increase debug level

4. linux kernel

linux kernel has to be patched with smashfs-kernel.patch.

patching linux kernel is quite easy:

# cd linux
# patch -p0 < smashfs.kernel.patch

enable smashfs, and compression methods from kernel config

* SmashFS - Smashed file system support
  * xz compression
  * lzo compression
  * lzma compression
  * gzip comression

5. using

6. contact

if you are using the software and/or have any questions, suggestions, etc. please contact with me at alper.akcan@gmail.com