# SPDX-License-Identifier: GPL-2.0-only
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config SQUASHFS
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tristate "SquashFS 4.0 - Squashed file system support"
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depends on BLOCK
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help
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Saying Y here includes support for SquashFS 4.0 (a Compressed
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Read-Only File System). Squashfs is a highly compressed read-only
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filesystem for Linux. It uses zlib, lzo or xz compression to
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compress both files, inodes and directories. Inodes in the system
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are very small and all blocks are packed to minimise data overhead.
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Block sizes greater than 4K are supported up to a maximum of 1 Mbytes
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(default block size 128K). SquashFS 4.0 supports 64 bit filesystems
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and files (larger than 4GB), full uid/gid information, hard links and
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timestamps.
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Squashfs is intended for general read-only filesystem use, for
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archival use (i.e. in cases where a .tar.gz file may be used), and in
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embedded systems where low overhead is needed. Further information
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and tools are available from http://squashfs.sourceforge.net.
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If you want to compile this as a module ( = code which can be
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inserted in and removed from the running kernel whenever you want),
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say M here. The module will be called squashfs. Note that the root
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file system (the one containing the directory /) cannot be compiled
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as a module.
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If unsure, say N.
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choice
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prompt "File decompression options"
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depends on SQUASHFS
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help
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Squashfs now supports two options for decompressing file
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data. Traditionally Squashfs has decompressed into an
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intermediate buffer and then memcopied it into the page cache.
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Squashfs now supports the ability to decompress directly into
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the page cache.
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If unsure, select "Decompress file data into an intermediate buffer"
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config SQUASHFS_FILE_CACHE
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bool "Decompress file data into an intermediate buffer"
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help
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Decompress file data into an intermediate buffer and then
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memcopy it into the page cache.
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config SQUASHFS_FILE_DIRECT
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bool "Decompress files directly into the page cache"
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help
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Directly decompress file data into the page cache.
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Doing so can significantly improve performance because
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it eliminates a memcpy and it also removes the lock contention
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on the single buffer.
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endchoice
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choice
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prompt "Decompressor parallelisation options"
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depends on SQUASHFS
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help
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Squashfs now supports three parallelisation options for
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decompression. Each one exhibits various trade-offs between
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decompression performance and CPU and memory usage.
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If in doubt, select "Single threaded compression"
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config SQUASHFS_DECOMP_SINGLE
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bool "Single threaded compression"
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help
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Traditionally Squashfs has used single-threaded decompression.
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Only one block (data or metadata) can be decompressed at any
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one time. This limits CPU and memory usage to a minimum.
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config SQUASHFS_DECOMP_MULTI
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bool "Use multiple decompressors for parallel I/O"
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help
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By default Squashfs uses a single decompressor but it gives
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poor performance on parallel I/O workloads when using multiple CPU
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machines due to waiting on decompressor availability.
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If you have a parallel I/O workload and your system has enough memory,
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using this option may improve overall I/O performance.
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This decompressor implementation uses up to two parallel
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decompressors per core. It dynamically allocates decompressors
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on a demand basis.
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config SQUASHFS_DECOMP_MULTI_PERCPU
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bool "Use percpu multiple decompressors for parallel I/O"
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help
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By default Squashfs uses a single decompressor but it gives
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poor performance on parallel I/O workloads when using multiple CPU
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machines due to waiting on decompressor availability.
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This decompressor implementation uses a maximum of one
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decompressor per core. It uses percpu variables to ensure
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decompression is load-balanced across the cores.
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endchoice
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config SQUASHFS_XATTR
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bool "Squashfs XATTR support"
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depends on SQUASHFS
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help
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Saying Y here includes support for extended attributes (xattrs).
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Xattrs are name:value pairs associated with inodes by
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the kernel or by users (see the attr(5) manual page).
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If unsure, say N.
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config SQUASHFS_ZLIB
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bool "Include support for ZLIB compressed file systems"
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depends on SQUASHFS
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select ZLIB_INFLATE
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default y
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help
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ZLIB compression is the standard compression used by Squashfs
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file systems. It offers a good trade-off between compression
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achieved and the amount of CPU time and memory necessary to
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compress and decompress.
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If unsure, say Y.
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config SQUASHFS_LZ4
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bool "Include support for LZ4 compressed file systems"
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depends on SQUASHFS
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select LZ4_DECOMPRESS
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help
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Saying Y here includes support for reading Squashfs file systems
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compressed with LZ4 compression. LZ4 compression is mainly
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aimed at embedded systems with slower CPUs where the overheads
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of zlib are too high.
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LZ4 is not the standard compression used in Squashfs and so most
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file systems will be readable without selecting this option.
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If unsure, say N.
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config SQUASHFS_LZO
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bool "Include support for LZO compressed file systems"
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depends on SQUASHFS
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select LZO_DECOMPRESS
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help
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Saying Y here includes support for reading Squashfs file systems
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compressed with LZO compression. LZO compression is mainly
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aimed at embedded systems with slower CPUs where the overheads
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of zlib are too high.
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LZO is not the standard compression used in Squashfs and so most
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file systems will be readable without selecting this option.
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If unsure, say N.
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config SQUASHFS_XZ
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bool "Include support for XZ compressed file systems"
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depends on SQUASHFS
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select XZ_DEC
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help
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Saying Y here includes support for reading Squashfs file systems
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compressed with XZ compression. XZ gives better compression than
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the default zlib compression, at the expense of greater CPU and
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memory overhead.
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XZ is not the standard compression used in Squashfs and so most
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file systems will be readable without selecting this option.
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If unsure, say N.
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config SQUASHFS_ZSTD
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bool "Include support for ZSTD compressed file systems"
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depends on SQUASHFS
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select ZSTD_DECOMPRESS
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help
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Saying Y here includes support for reading Squashfs file systems
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compressed with ZSTD compression. ZSTD gives better compression than
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the default ZLIB compression, while using less CPU.
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ZSTD is not the standard compression used in Squashfs and so most
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file systems will be readable without selecting this option.
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If unsure, say N.
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config SQUASHFS_4K_DEVBLK_SIZE
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bool "Use 4K device block size?"
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depends on SQUASHFS
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help
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By default Squashfs sets the dev block size (sb_min_blocksize)
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to 1K or the smallest block size supported by the block device
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(if larger). This, because blocks are packed together and
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unaligned in Squashfs, should reduce latency.
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This, however, gives poor performance on MTD NAND devices where
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the optimal I/O size is 4K (even though the devices can support
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smaller block sizes).
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Using a 4K device block size may also improve overall I/O
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performance for some file access patterns (e.g. sequential
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accesses of files in filesystem order) on all media.
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Setting this option will force Squashfs to use a 4K device block
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size by default.
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If unsure, say N.
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config SQUASHFS_EMBEDDED
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bool "Additional option for memory-constrained systems"
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depends on SQUASHFS
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help
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Saying Y here allows you to specify cache size.
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If unsure, say N.
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config SQUASHFS_FRAGMENT_CACHE_SIZE
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int "Number of fragments cached" if SQUASHFS_EMBEDDED
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depends on SQUASHFS
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default "3"
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help
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By default SquashFS caches the last 3 fragments read from
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the filesystem. Increasing this amount may mean SquashFS
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has to re-read fragments less often from disk, at the expense
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of extra system memory. Decreasing this amount will mean
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SquashFS uses less memory at the expense of extra reads from disk.
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Note there must be at least one cached fragment. Anything
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much more than three will probably not make much difference.
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