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/usr/src/linux-headers-5.15.0-190/usr/Kconfig
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# SPDX-License-Identifier: GPL-2.0 # # Configuration for initramfs # config INITRAMFS_SOURCE string "Initramfs source file(s)" default "" help This can be either a single cpio archive with a .cpio suffix or a space-separated list of directories and files for building the initramfs image. A cpio archive should contain a filesystem archive to be used as an initramfs image. Directories should contain a filesystem layout to be included in the initramfs image. Files should contain entries according to the format described by the "usr/gen_init_cpio" program in the kernel tree. When multiple directories and files are specified then the initramfs image will be the aggregate of all of them. See <file:Documentation/driver-api/early-userspace/early_userspace_support.rst> for more details. If you are not sure, leave it blank. config INITRAMFS_FORCE bool "Ignore the initramfs passed by the bootloader" depends on CMDLINE_EXTEND || CMDLINE_FORCE help This option causes the kernel to ignore the initramfs image (or initrd image) passed to it by the bootloader. This is analogous to CMDLINE_FORCE, which is found on some architectures, and is useful if you cannot or don't want to change the image your bootloader passes to the kernel. config INITRAMFS_ROOT_UID int "User ID to map to 0 (user root)" depends on INITRAMFS_SOURCE!="" default "0" help If INITRAMFS_SOURCE points to a directory, files owned by this UID (-1 = current user) will be owned by root in the resulting image. If you are not sure, leave it set to "0". config INITRAMFS_ROOT_GID int "Group ID to map to 0 (group root)" depends on INITRAMFS_SOURCE!="" default "0" help If INITRAMFS_SOURCE points to a directory, files owned by this GID (-1 = current group) will be owned by root in the resulting image. If you are not sure, leave it set to "0". config RD_GZIP bool "Support initial ramdisk/ramfs compressed using gzip" default y select DECOMPRESS_GZIP help Support loading of a gzip encoded initial ramdisk or cpio buffer. If unsure, say Y. config RD_BZIP2 bool "Support initial ramdisk/ramfs compressed using bzip2" default y select DECOMPRESS_BZIP2 help Support loading of a bzip2 encoded initial ramdisk or cpio buffer If unsure, say N. config RD_LZMA bool "Support initial ramdisk/ramfs compressed using LZMA" default y select DECOMPRESS_LZMA help Support loading of a LZMA encoded initial ramdisk or cpio buffer If unsure, say N. config RD_XZ bool "Support initial ramdisk/ramfs compressed using XZ" default y select DECOMPRESS_XZ help Support loading of a XZ encoded initial ramdisk or cpio buffer. If unsure, say N. config RD_LZO bool "Support initial ramdisk/ramfs compressed using LZO" default y select DECOMPRESS_LZO help Support loading of a LZO encoded initial ramdisk or cpio buffer If unsure, say N. config RD_LZ4 bool "Support initial ramdisk/ramfs compressed using LZ4" default y select DECOMPRESS_LZ4 help Support loading of a LZ4 encoded initial ramdisk or cpio buffer If unsure, say N. config RD_ZSTD bool "Support initial ramdisk/ramfs compressed using ZSTD" default y select DECOMPRESS_ZSTD help Support loading of a ZSTD encoded initial ramdisk or cpio buffer. If unsure, say N. choice prompt "Built-in initramfs compression mode" depends on INITRAMFS_SOURCE != "" help This option allows you to decide by which algorithm the builtin initramfs will be compressed. Several compression algorithms are available, which differ in efficiency, compression and decompression speed. Compression speed is only relevant when building a kernel. Decompression speed is relevant at each boot. Also the memory usage during decompression may become relevant on memory constrained systems. This is usually based on the dictionary size of the algorithm with algorithms like XZ and LZMA featuring large dictionary sizes. High compression options are mostly useful for users who are low on RAM, since it reduces the memory consumption during boot. Keep in mind that your build system needs to provide the appropriate compression tool to compress the generated initram cpio file for embedding. If in doubt, select 'None' config INITRAMFS_COMPRESSION_GZIP bool "Gzip" depends on RD_GZIP help Use the old and well tested gzip compression algorithm. Gzip provides a good balance between compression ratio and decompression speed and has a reasonable compression speed. It is also more likely to be supported by your build system as the gzip tool is present by default on most distros. config INITRAMFS_COMPRESSION_BZIP2 bool "Bzip2" depends on RD_BZIP2 help It's compression ratio and speed is intermediate. Decompression speed is slowest among the choices. The initramfs size is about 10% smaller with bzip2, in comparison to gzip. Bzip2 uses a large amount of memory. For modern kernels you will need at least 8MB RAM or more for booting. If you choose this, keep in mind that you need to have the bzip2 tool available to be able to compress the initram. config INITRAMFS_COMPRESSION_LZMA bool "LZMA" depends on RD_LZMA help This algorithm's compression ratio is best but has a large dictionary size which might cause issues in memory constrained systems. Decompression speed is between the other choices. Compression is slowest. The initramfs size is about 33% smaller with LZMA in comparison to gzip. If you choose this, keep in mind that you may need to install the xz or lzma tools to be able to compress the initram. config INITRAMFS_COMPRESSION_XZ bool "XZ" depends on RD_XZ help XZ uses the LZMA2 algorithm and has a large dictionary which may cause problems on memory constrained systems. The initramfs size is about 30% smaller with XZ in comparison to gzip. Decompression speed is better than that of bzip2 but worse than gzip and LZO. Compression is slow. If you choose this, keep in mind that you may need to install the xz tool to be able to compress the initram. config INITRAMFS_COMPRESSION_LZO bool "LZO" depends on RD_LZO help It's compression ratio is the second poorest amongst the choices. The kernel size is about 10% bigger than gzip. Despite that, it's decompression speed is the second fastest and it's compression speed is quite fast too. If you choose this, keep in mind that you may need to install the lzop tool to be able to compress the initram. config INITRAMFS_COMPRESSION_LZ4 bool "LZ4" depends on RD_LZ4 help It's compression ratio is the poorest amongst the choices. The kernel size is about 15% bigger than gzip; however its decompression speed is the fastest. If you choose this, keep in mind that most distros don't provide lz4 by default which could cause a build failure. config INITRAMFS_COMPRESSION_ZSTD bool "ZSTD" depends on RD_ZSTD help ZSTD is a compression algorithm targeting intermediate compression with fast decompression speed. It will compress better than GZIP and decompress around the same speed as LZO, but slower than LZ4. If you choose this, keep in mind that you may need to install the zstd tool to be able to compress the initram. config INITRAMFS_COMPRESSION_NONE bool "None" help Do not compress the built-in initramfs at all. This may sound wasteful in space, but, you should be aware that the built-in initramfs will be compressed at a later stage anyways along with the rest of the kernel, on those architectures that support this. However, not compressing the initramfs may lead to slightly higher memory consumption during a short time at boot, while both the cpio image and the unpacked filesystem image will be present in memory simultaneously endchoice
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