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Linux/fs/squashfs/Kconfig

  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_LZO
124         bool "Include support for LZO compressed file systems"
125         depends on SQUASHFS
126         select LZO_DECOMPRESS
127         help
128           Saying Y here includes support for reading Squashfs file systems
129           compressed with LZO compression.  LZO compression is mainly
130           aimed at embedded systems with slower CPUs where the overheads
131           of zlib are too high.
132 
133           LZO 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_XZ
139         bool "Include support for XZ compressed file systems"
140         depends on SQUASHFS
141         select XZ_DEC
142         help
143           Saying Y here includes support for reading Squashfs file systems
144           compressed with XZ compression.  XZ gives better compression than
145           the default zlib compression, at the expense of greater CPU and
146           memory overhead.
147 
148           XZ 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_4K_DEVBLK_SIZE
154         bool "Use 4K device block size?"
155         depends on SQUASHFS
156         help
157           By default Squashfs sets the dev block size (sb_min_blocksize)
158           to 1K or the smallest block size supported by the block device
159           (if larger).  This, because blocks are packed together and
160           unaligned in Squashfs, should reduce latency.
161 
162           This, however, gives poor performance on MTD NAND devices where
163           the optimal I/O size is 4K (even though the devices can support
164           smaller block sizes).
165 
166           Using a 4K device block size may also improve overall I/O
167           performance for some file access patterns (e.g. sequential
168           accesses of files in filesystem order) on all media.
169 
170           Setting this option will force Squashfs to use a 4K device block
171           size by default.
172 
173           If unsure, say N.
174 
175 config SQUASHFS_EMBEDDED
176         bool "Additional option for memory-constrained systems"
177         depends on SQUASHFS
178         help
179           Saying Y here allows you to specify cache size.
180 
181           If unsure, say N.
182 
183 config SQUASHFS_FRAGMENT_CACHE_SIZE
184         int "Number of fragments cached" if SQUASHFS_EMBEDDED
185         depends on SQUASHFS
186         default "3"
187         help
188           By default SquashFS caches the last 3 fragments read from
189           the filesystem.  Increasing this amount may mean SquashFS
190           has to re-read fragments less often from disk, at the expense
191           of extra system memory.  Decreasing this amount will mean
192           SquashFS uses less memory at the expense of extra reads from disk.
193 
194           Note there must be at least one cached fragment.  Anything
195           much more than three will probably not make much difference.

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