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Kconfig
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config SQUASHFS
tristate "SquashFS 4.0 - Squashed file system support"
depends on BLOCK
help
Saying Y here includes support for SquashFS 4.0 (a Compressed
Read-Only File System). Squashfs is a highly compressed read-only
filesystem for Linux. It uses zlib, lzo or xz compression to
compress both files, inodes and directories. Inodes in the system
are very small and all blocks are packed to minimise data overhead.
Block sizes greater than 4K are supported up to a maximum of 1 Mbytes
(default block size 128K). SquashFS 4.0 supports 64 bit filesystems
and files (larger than 4GB), full uid/gid information, hard links and
timestamps.
Squashfs is intended for general read-only filesystem use, for
archival use (i.e. in cases where a .tar.gz file may be used), and in
embedded systems where low overhead is needed. Further information
and tools are available from http://squashfs.sourceforge.net.
If you want to compile this as a module ( = code which can be
inserted in and removed from the running kernel whenever you want),
say M here. The module will be called squashfs. Note that the root
file system (the one containing the directory /) cannot be compiled
as a module.
If unsure, say N.
choice
prompt "File decompression options"
depends on SQUASHFS
help
Squashfs now supports two options for decompressing file
data. Traditionally Squashfs has decompressed into an
intermediate buffer and then memcopied it into the page cache.
Squashfs now supports the ability to decompress directly into
the page cache.
If unsure, select "Decompress file data into an intermediate buffer"
config SQUASHFS_FILE_CACHE
bool "Decompress file data into an intermediate buffer"
help
Decompress file data into an intermediate buffer and then
memcopy it into the page cache.
config SQUASHFS_FILE_DIRECT
bool "Decompress files directly into the page cache"
help
Directly decompress file data into the page cache.
Doing so can significantly improve performance because
it eliminates a memcpy and it also removes the lock contention
on the single buffer.
endchoice
choice
prompt "Decompressor parallelisation options"
depends on SQUASHFS
help
Squashfs now supports three parallelisation options for
decompression. Each one exhibits various trade-offs between
decompression performance and CPU and memory usage.
If in doubt, select "Single threaded compression"
config SQUASHFS_DECOMP_SINGLE
bool "Single threaded compression"
help
Traditionally Squashfs has used single-threaded decompression.
Only one block (data or metadata) can be decompressed at any
one time. This limits CPU and memory usage to a minimum.
config SQUASHFS_DECOMP_MULTI
bool "Use multiple decompressors for parallel I/O"
help
By default Squashfs uses a single decompressor but it gives
poor performance on parallel I/O workloads when using multiple CPU
machines due to waiting on decompressor availability.
If you have a parallel I/O workload and your system has enough memory,
using this option may improve overall I/O performance.
This decompressor implementation uses up to two parallel
decompressors per core. It dynamically allocates decompressors
on a demand basis.
config SQUASHFS_DECOMP_MULTI_PERCPU
bool "Use percpu multiple decompressors for parallel I/O"
help
By default Squashfs uses a single decompressor but it gives
poor performance on parallel I/O workloads when using multiple CPU
machines due to waiting on decompressor availability.
This decompressor implementation uses a maximum of one
decompressor per core. It uses percpu variables to ensure
decompression is load-balanced across the cores.
endchoice
config SQUASHFS_XATTR
bool "Squashfs XATTR support"
depends on SQUASHFS
help
Saying Y here includes support for extended attributes (xattrs).
Xattrs are name:value pairs associated with inodes by
the kernel or by users (see the attr(5) manual page).
If unsure, say N.
config SQUASHFS_ZLIB
bool "Include support for ZLIB compressed file systems"
depends on SQUASHFS
select ZLIB_INFLATE
default y
help
ZLIB compression is the standard compression used by Squashfs
file systems. It offers a good trade-off between compression
achieved and the amount of CPU time and memory necessary to
compress and decompress.
If unsure, say Y.
config SQUASHFS_LZ4
bool "Include support for LZ4 compressed file systems"
depends on SQUASHFS
select LZ4_DECOMPRESS
help
Saying Y here includes support for reading Squashfs file systems
compressed with LZ4 compression. LZ4 compression is mainly
aimed at embedded systems with slower CPUs where the overheads
of zlib are too high.
LZ4 is not the standard compression used in Squashfs and so most
file systems will be readable without selecting this option.
If unsure, say N.
config SQUASHFS_LZO
bool "Include support for LZO compressed file systems"
depends on SQUASHFS
select LZO_DECOMPRESS
help
Saying Y here includes support for reading Squashfs file systems
compressed with LZO compression. LZO compression is mainly
aimed at embedded systems with slower CPUs where the overheads
of zlib are too high.
LZO is not the standard compression used in Squashfs and so most
file systems will be readable without selecting this option.
If unsure, say N.
config SQUASHFS_XZ
bool "Include support for XZ compressed file systems"
depends on SQUASHFS
select XZ_DEC
help
Saying Y here includes support for reading Squashfs file systems
compressed with XZ compression. XZ gives better compression than
the default zlib compression, at the expense of greater CPU and
memory overhead.
XZ is not the standard compression used in Squashfs and so most
file systems will be readable without selecting this option.
If unsure, say N.
config SQUASHFS_ZSTD
bool "Include support for ZSTD compressed file systems"
depends on SQUASHFS
select ZSTD_DECOMPRESS
help
Saying Y here includes support for reading Squashfs file systems
compressed with ZSTD compression. ZSTD gives better compression than
the default ZLIB compression, while using less CPU.
ZSTD is not the standard compression used in Squashfs and so most
file systems will be readable without selecting this option.
If unsure, say N.
config SQUASHFS_4K_DEVBLK_SIZE
bool "Use 4K device block size?"
depends on SQUASHFS
help
By default Squashfs sets the dev block size (sb_min_blocksize)
to 1K or the smallest block size supported by the block device
(if larger). This, because blocks are packed together and
unaligned in Squashfs, should reduce latency.
This, however, gives poor performance on MTD NAND devices where
the optimal I/O size is 4K (even though the devices can support
smaller block sizes).
Using a 4K device block size may also improve overall I/O
performance for some file access patterns (e.g. sequential
accesses of files in filesystem order) on all media.
Setting this option will force Squashfs to use a 4K device block
size by default.
If unsure, say N.
config SQUASHFS_EMBEDDED
bool "Additional option for memory-constrained systems"
depends on SQUASHFS
help
Saying Y here allows you to specify cache size.
If unsure, say N.
config SQUASHFS_FRAGMENT_CACHE_SIZE
int "Number of fragments cached" if SQUASHFS_EMBEDDED
depends on SQUASHFS
default "3"
help
By default SquashFS caches the last 3 fragments read from
the filesystem. Increasing this amount may mean SquashFS
has to re-read fragments less often from disk, at the expense
of extra system memory. Decreasing this amount will mean
SquashFS uses less memory at the expense of extra reads from disk.
Note there must be at least one cached fragment. Anything
much more than three will probably not make much difference.