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 LZ4 compressed file systems"
100 Saying Y here includes support for reading Squashfs file systems
101 compressed with LZ4 compression. LZ4 compression is mainly
102 aimed at embedded systems with slower CPUs where the overheads
103 of zlib are too high.
105 LZ4 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 LZO compressed file systems"
113 select LZO_DECOMPRESS
115 Saying Y here includes support for reading Squashfs file systems
116 compressed with LZO compression. LZO compression is mainly
117 aimed at embedded systems with slower CPUs where the overheads
118 of zlib are too high.
120 LZO is not the standard compression used in Squashfs and so most
121 file systems will be readable without selecting this option.
126 bool "Include support for XZ compressed file systems"
130 Saying Y here includes support for reading Squashfs file systems
131 compressed with XZ compression. XZ gives better compression than
132 the default zlib compression, at the expense of greater CPU and
135 XZ is not the standard compression used in Squashfs and so most
136 file systems will be readable without selecting this option.
140 config SQUASHFS_4K_DEVBLK_SIZE
141 bool "Use 4K device block size?"
144 By default Squashfs sets the dev block size (sb_min_blocksize)
145 to 1K or the smallest block size supported by the block device
146 (if larger). This, because blocks are packed together and
147 unaligned in Squashfs, should reduce latency.
149 This, however, gives poor performance on MTD NAND devices where
150 the optimal I/O size is 4K (even though the devices can support
151 smaller block sizes).
153 Using a 4K device block size may also improve overall I/O
154 performance for some file access patterns (e.g. sequential
155 accesses of files in filesystem order) on all media.
157 Setting this option will force Squashfs to use a 4K device block
162 config SQUASHFS_EMBEDDED
163 bool "Additional option for memory-constrained systems"
166 Saying Y here allows you to specify cache size.
170 config SQUASHFS_FRAGMENT_CACHE_SIZE
171 int "Number of fragments cached" if SQUASHFS_EMBEDDED
175 By default SquashFS caches the last 3 fragments read from
176 the filesystem. Increasing this amount may mean SquashFS
177 has to re-read fragments less often from disk, at the expense
178 of extra system memory. Decreasing this amount will mean
179 SquashFS uses less memory at the expense of extra reads from disk.
181 Note there must be at least one cached fragment. Anything
182 much more than three will probably not make much difference.