Linux v6.6.1 - squashfs

# SPDX-License-Identifier: GPL-2.0-only
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

config SQUASHFS_DECOMP_SINGLE
	depends on SQUASHFS
	def_bool n

config SQUASHFS_DECOMP_MULTI
	depends on SQUASHFS
	def_bool n

config SQUASHFS_DECOMP_MULTI_PERCPU
	depends on SQUASHFS
	def_bool n

config SQUASHFS_CHOICE_DECOMP_BY_MOUNT
	bool "Select the parallel decompression mode during mount"
	depends on SQUASHFS
	default n
	select SQUASHFS_DECOMP_SINGLE
	select SQUASHFS_DECOMP_MULTI
	select SQUASHFS_DECOMP_MULTI_PERCPU
	select SQUASHFS_MOUNT_DECOMP_THREADS
	help
	  Compile all parallel decompression modes and specify the
	  decompression mode by setting "threads=" during mount.
	  default Decompressor parallelisation is SQUASHFS_DECOMP_SINGLE

choice
	prompt "Select decompression parallel mode at compile time"
	depends on SQUASHFS
	depends on !SQUASHFS_CHOICE_DECOMP_BY_MOUNT
	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_COMPILE_DECOMP_SINGLE
	bool "Single threaded compression"
	select SQUASHFS_DECOMP_SINGLE
	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_COMPILE_DECOMP_MULTI
	bool "Use multiple decompressors for parallel I/O"
	select SQUASHFS_DECOMP_MULTI
	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_COMPILE_DECOMP_MULTI_PERCPU
	bool "Use percpu multiple decompressors for parallel I/O"
	select SQUASHFS_DECOMP_MULTI_PERCPU
	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_MOUNT_DECOMP_THREADS
	bool "Add the mount parameter 'threads=' for squashfs"
	depends on SQUASHFS
	depends on SQUASHFS_DECOMP_MULTI
	default n
	help
	  Use threads= to set the decompression parallel mode and the number of threads.
	  If SQUASHFS_CHOICE_DECOMP_BY_MOUNT=y
	      threads=<single|multi|percpu|1|2|3|...>
	  else
	      threads=<2|3|...>
	  The upper limit is num_online_cpus() * 2.

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.