1 # SPDX-License-Identifier: GPL-2.0-only 2 config 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 29 choice 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 41 config 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 47 config 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 55 endchoice 56 57 config SQUASHFS_DECOMP_SINGLE 58 depends on SQUASHFS 59 def_bool n 60 61 config SQUASHFS_DECOMP_MULTI 62 depends on SQUASHFS 63 def_bool n 64 65 config SQUASHFS_DECOMP_MULTI_PERCPU 66 depends on SQUASHFS 67 def_bool n 68 69 config SQUASHFS_CHOICE_DECOMP_BY_MOUNT 70 bool "Select the parallel decompression mode during mount" 71 depends on SQUASHFS 72 default n 73 select SQUASHFS_DECOMP_SINGLE 74 select SQUASHFS_DECOMP_MULTI 75 select SQUASHFS_DECOMP_MULTI_PERCPU 76 select SQUASHFS_MOUNT_DECOMP_THREADS 77 help 78 Compile all parallel decompression modes and specify the 79 decompression mode by setting "threads=" during mount. 80 default Decompressor parallelisation is SQUASHFS_DECOMP_SINGLE 81 82 choice 83 prompt "Select decompression parallel mode at compile time" 84 depends on SQUASHFS 85 depends on !SQUASHFS_CHOICE_DECOMP_BY_MOUNT 86 help 87 Squashfs now supports three parallelisation options for 88 decompression. Each one exhibits various trade-offs between 89 decompression performance and CPU and memory usage. 90 91 If in doubt, select "Single threaded compression" 92 93 config SQUASHFS_COMPILE_DECOMP_SINGLE 94 bool "Single threaded compression" 95 select SQUASHFS_DECOMP_SINGLE 96 help 97 Traditionally Squashfs has used single-threaded decompression. 98 Only one block (data or metadata) can be decompressed at any 99 one time. This limits CPU and memory usage to a minimum. 100 101 config SQUASHFS_COMPILE_DECOMP_MULTI 102 bool "Use multiple decompressors for parallel I/O" 103 select SQUASHFS_DECOMP_MULTI 104 help 105 By default Squashfs uses a single decompressor but it gives 106 poor performance on parallel I/O workloads when using multiple CPU 107 machines due to waiting on decompressor availability. 108 109 If you have a parallel I/O workload and your system has enough memory, 110 using this option may improve overall I/O performance. 111 112 This decompressor implementation uses up to two parallel 113 decompressors per core. It dynamically allocates decompressors 114 on a demand basis. 115 116 config SQUASHFS_COMPILE_DECOMP_MULTI_PERCPU 117 bool "Use percpu multiple decompressors for parallel I/O" 118 select SQUASHFS_DECOMP_MULTI_PERCPU 119 help 120 By default Squashfs uses a single decompressor but it gives 121 poor performance on parallel I/O workloads when using multiple CPU 122 machines due to waiting on decompressor availability. 123 124 This decompressor implementation uses a maximum of one 125 decompressor per core. It uses percpu variables to ensure 126 decompression is load-balanced across the cores. 127 endchoice 128 129 config SQUASHFS_MOUNT_DECOMP_THREADS 130 bool "Add the mount parameter 'threads=' for squashfs" 131 depends on SQUASHFS 132 depends on SQUASHFS_DECOMP_MULTI 133 default n 134 help 135 Use threads= to set the decompression parallel mode and the number of threads. 136 If SQUASHFS_CHOICE_DECOMP_BY_MOUNT=y 137 threads=<single|multi|percpu|1|2|3|...> 138 else 139 threads=<2|3|...> 140 The upper limit is num_online_cpus() * 2. 141 142 config SQUASHFS_XATTR 143 bool "Squashfs XATTR support" 144 depends on SQUASHFS 145 help 146 Saying Y here includes support for extended attributes (xattrs). 147 Xattrs are name:value pairs associated with inodes by 148 the kernel or by users (see the attr(5) manual page). 149 150 If unsure, say N. 151 152 config SQUASHFS_ZLIB 153 bool "Include support for ZLIB compressed file systems" 154 depends on SQUASHFS 155 select ZLIB_INFLATE 156 default y 157 help 158 ZLIB compression is the standard compression used by Squashfs 159 file systems. It offers a good trade-off between compression 160 achieved and the amount of CPU time and memory necessary to 161 compress and decompress. 162 163 If unsure, say Y. 164 165 config SQUASHFS_LZ4 166 bool "Include support for LZ4 compressed file systems" 167 depends on SQUASHFS 168 select LZ4_DECOMPRESS 169 help 170 Saying Y here includes support for reading Squashfs file systems 171 compressed with LZ4 compression. LZ4 compression is mainly 172 aimed at embedded systems with slower CPUs where the overheads 173 of zlib are too high. 174 175 LZ4 is not the standard compression used in Squashfs and so most 176 file systems will be readable without selecting this option. 177 178 If unsure, say N. 179 180 config SQUASHFS_LZO 181 bool "Include support for LZO compressed file systems" 182 depends on SQUASHFS 183 select LZO_DECOMPRESS 184 help 185 Saying Y here includes support for reading Squashfs file systems 186 compressed with LZO compression. LZO compression is mainly 187 aimed at embedded systems with slower CPUs where the overheads 188 of zlib are too high. 189 190 LZO is not the standard compression used in Squashfs and so most 191 file systems will be readable without selecting this option. 192 193 If unsure, say N. 194 195 config SQUASHFS_XZ 196 bool "Include support for XZ compressed file systems" 197 depends on SQUASHFS 198 select XZ_DEC 199 help 200 Saying Y here includes support for reading Squashfs file systems 201 compressed with XZ compression. XZ gives better compression than 202 the default zlib compression, at the expense of greater CPU and 203 memory overhead. 204 205 XZ is not the standard compression used in Squashfs and so most 206 file systems will be readable without selecting this option. 207 208 If unsure, say N. 209 210 config SQUASHFS_ZSTD 211 bool "Include support for ZSTD compressed file systems" 212 depends on SQUASHFS 213 select ZSTD_DECOMPRESS 214 help 215 Saying Y here includes support for reading Squashfs file systems 216 compressed with ZSTD compression. ZSTD gives better compression than 217 the default ZLIB compression, while using less CPU. 218 219 ZSTD is not the standard compression used in Squashfs and so most 220 file systems will be readable without selecting this option. 221 222 If unsure, say N. 223 224 config SQUASHFS_4K_DEVBLK_SIZE 225 bool "Use 4K device block size?" 226 depends on SQUASHFS 227 help 228 By default Squashfs sets the dev block size (sb_min_blocksize) 229 to 1K or the smallest block size supported by the block device 230 (if larger). This, because blocks are packed together and 231 unaligned in Squashfs, should reduce latency. 232 233 This, however, gives poor performance on MTD NAND devices where 234 the optimal I/O size is 4K (even though the devices can support 235 smaller block sizes). 236 237 Using a 4K device block size may also improve overall I/O 238 performance for some file access patterns (e.g. sequential 239 accesses of files in filesystem order) on all media. 240 241 Setting this option will force Squashfs to use a 4K device block 242 size by default. 243 244 If unsure, say N. 245 246 config SQUASHFS_EMBEDDED 247 bool "Additional option for memory-constrained systems" 248 depends on SQUASHFS 249 help 250 Saying Y here allows you to specify cache size. 251 252 If unsure, say N. 253 254 config SQUASHFS_FRAGMENT_CACHE_SIZE 255 int "Number of fragments cached" if SQUASHFS_EMBEDDED 256 depends on SQUASHFS 257 default "3" 258 help 259 By default SquashFS caches the last 3 fragments read from 260 the filesystem. Increasing this amount may mean SquashFS 261 has to re-read fragments less often from disk, at the expense 262 of extra system memory. Decreasing this amount will mean 263 SquashFS uses less memory at the expense of extra reads from disk. 264 265 Note there must be at least one cached fragment. Anything 266 much more than three will probably not make much difference.
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