2 tristate "SquashFS 4.0 - Squashed file system support"
5 Saying Y here includes support for SquashFS 4.0 (a Compressed
6 Read-Only File System). Squashfs is a highly compressed read-only
7 filesystem for Linux. It uses zlib, lzo or xz compression to
8 compress both files, inodes and directories. Inodes in the system
9 are very small and all blocks are packed to minimise data overhead.
10 Block sizes greater than 4K are supported up to a maximum of 1 Mbytes
11 (default block size 128K). SquashFS 4.0 supports 64 bit filesystems
12 and files (larger than 4GB), full uid/gid information, hard links and
15 Squashfs is intended for general read-only filesystem use, for
16 archival use (i.e. in cases where a .tar.gz file may be used), and in
17 embedded systems where low overhead is needed. Further information
18 and tools are available from http://squashfs.sourceforge.net.
20 If you want to compile this as a module ( = code which can be
21 inserted in and removed from the running kernel whenever you want),
22 say M here. The module will be called squashfs. Note that the root
23 file system (the one containing the directory /) cannot be compiled
29 prompt "Decompressor parallelisation options"
32 Squashfs now supports three parallelisation options for
33 decompression. Each one exhibits various trade-offs between
34 decompression performance and CPU and memory usage.
36 If in doubt, select "Single threaded compression"
38 config SQUASHFS_DECOMP_SINGLE
39 bool "Single threaded compression"
41 Traditionally Squashfs has used single-threaded decompression.
42 Only one block (data or metadata) can be decompressed at any
43 one time. This limits CPU and memory usage to a minimum.
45 config SQUASHFS_DECOMP_MULTI
46 bool "Use multiple decompressors for parallel I/O"
48 By default Squashfs uses a single decompressor but it gives
49 poor performance on parallel I/O workloads when using multiple CPU
50 machines due to waiting on decompressor availability.
52 If you have a parallel I/O workload and your system has enough memory,
53 using this option may improve overall I/O performance.
55 This decompressor implementation uses up to two parallel
56 decompressors per core. It dynamically allocates decompressors
59 config SQUASHFS_DECOMP_MULTI_PERCPU
60 bool "Use percpu multiple decompressors for parallel I/O"
62 By default Squashfs uses a single decompressor but it gives
63 poor performance on parallel I/O workloads when using multiple CPU
64 machines due to waiting on decompressor availability.
66 This decompressor implementation uses a maximum of one
67 decompressor per core. It uses percpu variables to ensure
68 decompression is load-balanced across the cores.
73 bool "Squashfs XATTR support"
76 Saying Y here includes support for extended attributes (xattrs).
77 Xattrs are name:value pairs associated with inodes by
78 the kernel or by users (see the attr(5) manual page).
83 bool "Include support for ZLIB compressed file systems"
88 ZLIB compression is the standard compression used by Squashfs
89 file systems. It offers a good trade-off between compression
90 achieved and the amount of CPU time and memory necessary to
91 compress and decompress.
96 bool "Include support for LZO compressed file systems"
100 Saying Y here includes support for reading Squashfs file systems
101 compressed with LZO compression. LZO compression is mainly
102 aimed at embedded systems with slower CPUs where the overheads
103 of zlib are too high.
105 LZO is not the standard compression used in Squashfs and so most
106 file systems will be readable without selecting this option.
111 bool "Include support for XZ compressed file systems"
115 Saying Y here includes support for reading Squashfs file systems
116 compressed with XZ compression. XZ gives better compression than
117 the default zlib compression, at the expense of greater CPU and
120 XZ is not the standard compression used in Squashfs and so most
121 file systems will be readable without selecting this option.
125 config SQUASHFS_4K_DEVBLK_SIZE
126 bool "Use 4K device block size?"
129 By default Squashfs sets the dev block size (sb_min_blocksize)
130 to 1K or the smallest block size supported by the block device
131 (if larger). This, because blocks are packed together and
132 unaligned in Squashfs, should reduce latency.
134 This, however, gives poor performance on MTD NAND devices where
135 the optimal I/O size is 4K (even though the devices can support
136 smaller block sizes).
138 Using a 4K device block size may also improve overall I/O
139 performance for some file access patterns (e.g. sequential
140 accesses of files in filesystem order) on all media.
142 Setting this option will force Squashfs to use a 4K device block
147 config SQUASHFS_EMBEDDED
148 bool "Additional option for memory-constrained systems"
151 Saying Y here allows you to specify cache size.
155 config SQUASHFS_FRAGMENT_CACHE_SIZE
156 int "Number of fragments cached" if SQUASHFS_EMBEDDED
160 By default SquashFS caches the last 3 fragments read from
161 the filesystem. Increasing this amount may mean SquashFS
162 has to re-read fragments less often from disk, at the expense
163 of extra system memory. Decreasing this amount will mean
164 SquashFS uses less memory at the expense of extra reads from disk.
166 Note there must be at least one cached fragment. Anything
167 much more than three will probably not make much difference.