1 config SQUASHFS 2 tristate "SquashFS 4.0 - Squashed file system support" 3 depends on BLOCK 4 help 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 13 timestamps. 14 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. 19 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 24 as a module. 25 26 If unsure, say N. 27 28 choice 29 prompt "File decompression options" 30 depends on SQUASHFS 31 help 32 Squashfs now supports two options for decompressing file 33 data. Traditionally Squashfs has decompressed into an 34 intermediate buffer and then memcopied it into the page cache. 35 Squashfs now supports the ability to decompress directly into 36 the page cache. 37 38 If unsure, select "Decompress file data into an intermediate buffer" 39 40 config SQUASHFS_FILE_CACHE 41 bool "Decompress file data into an intermediate buffer" 42 help 43 Decompress file data into an intermediate buffer and then 44 memcopy it into the page cache. 45 46 config SQUASHFS_FILE_DIRECT 47 bool "Decompress files directly into the page cache" 48 help 49 Directly decompress file data into the page cache. 50 Doing so can significantly improve performance because 51 it eliminates a memcpy and it also removes the lock contention 52 on the single buffer. 53 54 endchoice 55 56 choice 57 prompt "Decompressor parallelisation options" 58 depends on SQUASHFS 59 help 60 Squashfs now supports three parallelisation options for 61 decompression. Each one exhibits various trade-offs between 62 decompression performance and CPU and memory usage. 63 64 If in doubt, select "Single threaded compression" 65 66 config SQUASHFS_DECOMP_SINGLE 67 bool "Single threaded compression" 68 help 69 Traditionally Squashfs has used single-threaded decompression. 70 Only one block (data or metadata) can be decompressed at any 71 one time. This limits CPU and memory usage to a minimum. 72 73 config SQUASHFS_DECOMP_MULTI 74 bool "Use multiple decompressors for parallel I/O" 75 help 76 By default Squashfs uses a single decompressor but it gives 77 poor performance on parallel I/O workloads when using multiple CPU 78 machines due to waiting on decompressor availability. 79 80 If you have a parallel I/O workload and your system has enough memory, 81 using this option may improve overall I/O performance. 82 83 This decompressor implementation uses up to two parallel 84 decompressors per core. It dynamically allocates decompressors 85 on a demand basis. 86 87 config SQUASHFS_DECOMP_MULTI_PERCPU 88 bool "Use percpu multiple decompressors for parallel I/O" 89 help 90 By default Squashfs uses a single decompressor but it gives 91 poor performance on parallel I/O workloads when using multiple CPU 92 machines due to waiting on decompressor availability. 93 94 This decompressor implementation uses a maximum of one 95 decompressor per core. It uses percpu variables to ensure 96 decompression is load-balanced across the cores. 97 98 endchoice 99 100 config SQUASHFS_XATTR 101 bool "Squashfs XATTR support" 102 depends on SQUASHFS 103 help 104 Saying Y here includes support for extended attributes (xattrs). 105 Xattrs are name:value pairs associated with inodes by 106 the kernel or by users (see the attr(5) manual page). 107 108 If unsure, say N. 109 110 config SQUASHFS_ZLIB 111 bool "Include support for ZLIB compressed file systems" 112 depends on SQUASHFS 113 select ZLIB_INFLATE 114 default y 115 help 116 ZLIB compression is the standard compression used by Squashfs 117 file systems. It offers a good trade-off between compression 118 achieved and the amount of CPU time and memory necessary to 119 compress and decompress. 120 121 If unsure, say Y. 122 123 config SQUASHFS_LZ4 124 bool "Include support for LZ4 compressed file systems" 125 depends on SQUASHFS 126 select LZ4_DECOMPRESS 127 help 128 Saying Y here includes support for reading Squashfs file systems 129 compressed with LZ4 compression. LZ4 compression is mainly 130 aimed at embedded systems with slower CPUs where the overheads 131 of zlib are too high. 132 133 LZ4 is not the standard compression used in Squashfs and so most 134 file systems will be readable without selecting this option. 135 136 If unsure, say N. 137 138 config SQUASHFS_LZO 139 bool "Include support for LZO compressed file systems" 140 depends on SQUASHFS 141 select LZO_DECOMPRESS 142 help 143 Saying Y here includes support for reading Squashfs file systems 144 compressed with LZO compression. LZO compression is mainly 145 aimed at embedded systems with slower CPUs where the overheads 146 of zlib are too high. 147 148 LZO is not the standard compression used in Squashfs and so most 149 file systems will be readable without selecting this option. 150 151 If unsure, say N. 152 153 config SQUASHFS_XZ 154 bool "Include support for XZ compressed file systems" 155 depends on SQUASHFS 156 select XZ_DEC 157 help 158 Saying Y here includes support for reading Squashfs file systems 159 compressed with XZ compression. XZ gives better compression than 160 the default zlib compression, at the expense of greater CPU and 161 memory overhead. 162 163 XZ is not the standard compression used in Squashfs and so most 164 file systems will be readable without selecting this option. 165 166 If unsure, say N. 167 168 config SQUASHFS_4K_DEVBLK_SIZE 169 bool "Use 4K device block size?" 170 depends on SQUASHFS 171 help 172 By default Squashfs sets the dev block size (sb_min_blocksize) 173 to 1K or the smallest block size supported by the block device 174 (if larger). This, because blocks are packed together and 175 unaligned in Squashfs, should reduce latency. 176 177 This, however, gives poor performance on MTD NAND devices where 178 the optimal I/O size is 4K (even though the devices can support 179 smaller block sizes). 180 181 Using a 4K device block size may also improve overall I/O 182 performance for some file access patterns (e.g. sequential 183 accesses of files in filesystem order) on all media. 184 185 Setting this option will force Squashfs to use a 4K device block 186 size by default. 187 188 If unsure, say N. 189 190 config SQUASHFS_EMBEDDED 191 bool "Additional option for memory-constrained systems" 192 depends on SQUASHFS 193 help 194 Saying Y here allows you to specify cache size. 195 196 If unsure, say N. 197 198 config SQUASHFS_FRAGMENT_CACHE_SIZE 199 int "Number of fragments cached" if SQUASHFS_EMBEDDED 200 depends on SQUASHFS 201 default "3" 202 help 203 By default SquashFS caches the last 3 fragments read from 204 the filesystem. Increasing this amount may mean SquashFS 205 has to re-read fragments less often from disk, at the expense 206 of extra system memory. Decreasing this amount will mean 207 SquashFS uses less memory at the expense of extra reads from disk. 208 209 Note there must be at least one cached fragment. Anything 210 much more than three will probably not make much difference.