Kconfig (8020B)
1# SPDX-License-Identifier: GPL-2.0-only 2config SQUASHFS 3 tristate "SquashFS 4.0 - Squashed file system support" 4 depends on BLOCK 5 help 6 Saying Y here includes support for SquashFS 4.0 (a Compressed 7 Read-Only File System). Squashfs is a highly compressed read-only 8 filesystem for Linux. It uses zlib, lzo or xz compression to 9 compress both files, inodes and directories. Inodes in the system 10 are very small and all blocks are packed to minimise data overhead. 11 Block sizes greater than 4K are supported up to a maximum of 1 Mbytes 12 (default block size 128K). SquashFS 4.0 supports 64 bit filesystems 13 and files (larger than 4GB), full uid/gid information, hard links and 14 timestamps. 15 16 Squashfs is intended for general read-only filesystem use, for 17 archival use (i.e. in cases where a .tar.gz file may be used), and in 18 embedded systems where low overhead is needed. Further information 19 and tools are available from http://squashfs.sourceforge.net. 20 21 If you want to compile this as a module ( = code which can be 22 inserted in and removed from the running kernel whenever you want), 23 say M here. The module will be called squashfs. Note that the root 24 file system (the one containing the directory /) cannot be compiled 25 as a module. 26 27 If unsure, say N. 28 29choice 30 prompt "File decompression options" 31 depends on SQUASHFS 32 help 33 Squashfs now supports two options for decompressing file 34 data. Traditionally Squashfs has decompressed into an 35 intermediate buffer and then memcopied it into the page cache. 36 Squashfs now supports the ability to decompress directly into 37 the page cache. 38 39 If unsure, select "Decompress file data into an intermediate buffer" 40 41config SQUASHFS_FILE_CACHE 42 bool "Decompress file data into an intermediate buffer" 43 help 44 Decompress file data into an intermediate buffer and then 45 memcopy it into the page cache. 46 47config SQUASHFS_FILE_DIRECT 48 bool "Decompress files directly into the page cache" 49 help 50 Directly decompress file data into the page cache. 51 Doing so can significantly improve performance because 52 it eliminates a memcpy and it also removes the lock contention 53 on the single buffer. 54 55endchoice 56 57choice 58 prompt "Decompressor parallelisation options" 59 depends on SQUASHFS 60 help 61 Squashfs now supports three parallelisation options for 62 decompression. Each one exhibits various trade-offs between 63 decompression performance and CPU and memory usage. 64 65 If in doubt, select "Single threaded compression" 66 67config SQUASHFS_DECOMP_SINGLE 68 bool "Single threaded compression" 69 help 70 Traditionally Squashfs has used single-threaded decompression. 71 Only one block (data or metadata) can be decompressed at any 72 one time. This limits CPU and memory usage to a minimum. 73 74config SQUASHFS_DECOMP_MULTI 75 bool "Use multiple decompressors for parallel I/O" 76 help 77 By default Squashfs uses a single decompressor but it gives 78 poor performance on parallel I/O workloads when using multiple CPU 79 machines due to waiting on decompressor availability. 80 81 If you have a parallel I/O workload and your system has enough memory, 82 using this option may improve overall I/O performance. 83 84 This decompressor implementation uses up to two parallel 85 decompressors per core. It dynamically allocates decompressors 86 on a demand basis. 87 88config SQUASHFS_DECOMP_MULTI_PERCPU 89 bool "Use percpu multiple decompressors for parallel I/O" 90 help 91 By default Squashfs uses a single decompressor but it gives 92 poor performance on parallel I/O workloads when using multiple CPU 93 machines due to waiting on decompressor availability. 94 95 This decompressor implementation uses a maximum of one 96 decompressor per core. It uses percpu variables to ensure 97 decompression is load-balanced across the cores. 98 99endchoice 100 101config SQUASHFS_XATTR 102 bool "Squashfs XATTR support" 103 depends on SQUASHFS 104 help 105 Saying Y here includes support for extended attributes (xattrs). 106 Xattrs are name:value pairs associated with inodes by 107 the kernel or by users (see the attr(5) manual page). 108 109 If unsure, say N. 110 111config SQUASHFS_ZLIB 112 bool "Include support for ZLIB compressed file systems" 113 depends on SQUASHFS 114 select ZLIB_INFLATE 115 default y 116 help 117 ZLIB compression is the standard compression used by Squashfs 118 file systems. It offers a good trade-off between compression 119 achieved and the amount of CPU time and memory necessary to 120 compress and decompress. 121 122 If unsure, say Y. 123 124config SQUASHFS_LZ4 125 bool "Include support for LZ4 compressed file systems" 126 depends on SQUASHFS 127 select LZ4_DECOMPRESS 128 help 129 Saying Y here includes support for reading Squashfs file systems 130 compressed with LZ4 compression. LZ4 compression is mainly 131 aimed at embedded systems with slower CPUs where the overheads 132 of zlib are too high. 133 134 LZ4 is not the standard compression used in Squashfs and so most 135 file systems will be readable without selecting this option. 136 137 If unsure, say N. 138 139config SQUASHFS_LZO 140 bool "Include support for LZO compressed file systems" 141 depends on SQUASHFS 142 select LZO_DECOMPRESS 143 help 144 Saying Y here includes support for reading Squashfs file systems 145 compressed with LZO compression. LZO compression is mainly 146 aimed at embedded systems with slower CPUs where the overheads 147 of zlib are too high. 148 149 LZO is not the standard compression used in Squashfs and so most 150 file systems will be readable without selecting this option. 151 152 If unsure, say N. 153 154config SQUASHFS_XZ 155 bool "Include support for XZ compressed file systems" 156 depends on SQUASHFS 157 select XZ_DEC 158 help 159 Saying Y here includes support for reading Squashfs file systems 160 compressed with XZ compression. XZ gives better compression than 161 the default zlib compression, at the expense of greater CPU and 162 memory overhead. 163 164 XZ is not the standard compression used in Squashfs and so most 165 file systems will be readable without selecting this option. 166 167 If unsure, say N. 168 169config SQUASHFS_ZSTD 170 bool "Include support for ZSTD compressed file systems" 171 depends on SQUASHFS 172 select ZSTD_DECOMPRESS 173 help 174 Saying Y here includes support for reading Squashfs file systems 175 compressed with ZSTD compression. ZSTD gives better compression than 176 the default ZLIB compression, while using less CPU. 177 178 ZSTD is not the standard compression used in Squashfs and so most 179 file systems will be readable without selecting this option. 180 181 If unsure, say N. 182 183config SQUASHFS_4K_DEVBLK_SIZE 184 bool "Use 4K device block size?" 185 depends on SQUASHFS 186 help 187 By default Squashfs sets the dev block size (sb_min_blocksize) 188 to 1K or the smallest block size supported by the block device 189 (if larger). This, because blocks are packed together and 190 unaligned in Squashfs, should reduce latency. 191 192 This, however, gives poor performance on MTD NAND devices where 193 the optimal I/O size is 4K (even though the devices can support 194 smaller block sizes). 195 196 Using a 4K device block size may also improve overall I/O 197 performance for some file access patterns (e.g. sequential 198 accesses of files in filesystem order) on all media. 199 200 Setting this option will force Squashfs to use a 4K device block 201 size by default. 202 203 If unsure, say N. 204 205config SQUASHFS_EMBEDDED 206 bool "Additional option for memory-constrained systems" 207 depends on SQUASHFS 208 help 209 Saying Y here allows you to specify cache size. 210 211 If unsure, say N. 212 213config SQUASHFS_FRAGMENT_CACHE_SIZE 214 int "Number of fragments cached" if SQUASHFS_EMBEDDED 215 depends on SQUASHFS 216 default "3" 217 help 218 By default SquashFS caches the last 3 fragments read from 219 the filesystem. Increasing this amount may mean SquashFS 220 has to re-read fragments less often from disk, at the expense 221 of extra system memory. Decreasing this amount will mean 222 SquashFS uses less memory at the expense of extra reads from disk. 223 224 Note there must be at least one cached fragment. Anything 225 much more than three will probably not make much difference.