tjh.dev
Linux kernel mirror (for testing)
git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
kernel
os
linux
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
57config SQUASHFS_DECOMP_SINGLE
58 depends on SQUASHFS
59 def_bool n
60
61config SQUASHFS_DECOMP_MULTI
62 depends on SQUASHFS
63 def_bool n
64
65config SQUASHFS_DECOMP_MULTI_PERCPU
66 depends on SQUASHFS
67 def_bool n
68
69config 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
82choice
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
93config 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
101config 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
116config 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.
127endchoice
128
129config 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
142config 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
152config 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
165config 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
180config 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
195config 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
210config 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
224config 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
246config 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
254config 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.