usr/Kconfig

   1 # SPDX-License-Identifier: GPL-2.0
   2 #
   3 # Configuration for initramfs
   4 #
   5
   6 config INITRAMFS_SOURCE
   7         string "Initramfs source file(s)"
   8         default ""
   9         help
  10           This can be either a single cpio archive with a .cpio suffix or a
  11           space-separated list of directories and files for building the
  12           initramfs image.  A cpio archive should contain a filesystem archive
  13           to be used as an initramfs image.  Directories should contain a
  14           filesystem layout to be included in the initramfs image.  Files
  15           should contain entries according to the format described by the
  16           "usr/gen_init_cpio" program in the kernel tree.
  17
  18           When multiple directories and files are specified then the
  19           initramfs image will be the aggregate of all of them.
  20
  21           See <file:Documentation/driver-api/early-userspace/early_userspace_support.rst> for more details.
  22
  23           If you are not sure, leave it blank.
  24
  25 config INITRAMFS_FORCE
  26         bool "Ignore the initramfs passed by the bootloader"
  27         depends on CMDLINE_EXTEND || CMDLINE_FORCE
  28         help
  29           This option causes the kernel to ignore the initramfs image
  30           (or initrd image) passed to it by the bootloader. This is
  31           analogous to CMDLINE_FORCE, which is found on some architectures,
  32           and is useful if you cannot or don't want to change the image
  33           your bootloader passes to the kernel.
  34
  35 config INITRAMFS_ROOT_UID
  36         int "User ID to map to 0 (user root)"
  37         depends on INITRAMFS_SOURCE!=""
  38         default "0"
  39         help
  40           If INITRAMFS_SOURCE points to a directory, files owned by this UID
  41           (-1 = current user) will be owned by root in the resulting image.
  42
  43           If you are not sure, leave it set to "0".
  44
  45 config INITRAMFS_ROOT_GID
  46         int "Group ID to map to 0 (group root)"
  47         depends on INITRAMFS_SOURCE!=""
  48         default "0"
  49         help
  50           If INITRAMFS_SOURCE points to a directory, files owned by this GID
  51           (-1 = current group) will be owned by root in the resulting image.
  52
  53           If you are not sure, leave it set to "0".
  54
  55 config RD_GZIP
  56         bool "Support initial ramdisk/ramfs compressed using gzip"
  57         default y
  58         select DECOMPRESS_GZIP
  59         help
  60           Support loading of a gzip encoded initial ramdisk or cpio buffer.
  61           If unsure, say Y.
  62
  63 config RD_BZIP2
  64         bool "Support initial ramdisk/ramfs compressed using bzip2"
  65         default y
  66         select DECOMPRESS_BZIP2
  67         help
  68           Support loading of a bzip2 encoded initial ramdisk or cpio buffer
  69           If unsure, say N.
  70
  71 config RD_LZMA
  72         bool "Support initial ramdisk/ramfs compressed using LZMA"
  73         default y
  74         select DECOMPRESS_LZMA
  75         help
  76           Support loading of a LZMA encoded initial ramdisk or cpio buffer
  77           If unsure, say N.
  78
  79 config RD_XZ
  80         bool "Support initial ramdisk/ramfs compressed using XZ"
  81         default y
  82         select DECOMPRESS_XZ
  83         help
  84           Support loading of a XZ encoded initial ramdisk or cpio buffer.
  85           If unsure, say N.
  86
  87 config RD_LZO
  88         bool "Support initial ramdisk/ramfs compressed using LZO"
  89         default y
  90         select DECOMPRESS_LZO
  91         help
  92           Support loading of a LZO encoded initial ramdisk or cpio buffer
  93           If unsure, say N.
  94
  95 config RD_LZ4
  96         bool "Support initial ramdisk/ramfs compressed using LZ4"
  97         default y
  98         select DECOMPRESS_LZ4
  99         help
 100           Support loading of a LZ4 encoded initial ramdisk or cpio buffer
 101           If unsure, say N.
 102
 103 choice
 104         prompt "Built-in initramfs compression mode"
 105         depends on INITRAMFS_SOURCE != ""
 106         help
 107           This option allows you to decide by which algorithm the builtin
 108           initramfs will be compressed.  Several compression algorithms are
 109           available, which differ in efficiency, compression and
 110           decompression speed.  Compression speed is only relevant
 111           when building a kernel.  Decompression speed is relevant at
 112           each boot. Also the memory usage during decompression may become
 113           relevant on memory constrained systems. This is usually based on the
 114           dictionary size of the algorithm with algorithms like XZ and LZMA
 115           featuring large dictionary sizes.
 116
 117           High compression options are mostly useful for users who are
 118           low on RAM, since it reduces the memory consumption during
 119           boot.
 120
 121           Keep in mind that your build system needs to provide the appropriate
 122           compression tool to compress the generated initram cpio file for
 123           embedding.
 124
 125           If in doubt, select 'None'
 126
 127 config INITRAMFS_COMPRESSION_NONE
 128         bool "None"
 129         help
 130           Do not compress the built-in initramfs at all. This may sound wasteful
 131           in space, but, you should be aware that the built-in initramfs will be
 132           compressed at a later stage anyways along with the rest of the kernel,
 133           on those architectures that support this. However, not compressing the
 134           initramfs may lead to slightly higher memory consumption during a
 135           short time at boot, while both the cpio image and the unpacked
 136           filesystem image will be present in memory simultaneously
 137
 138 config INITRAMFS_COMPRESSION_GZIP
 139         bool "Gzip"
 140         depends on RD_GZIP
 141         help
 142           Use the old and well tested gzip compression algorithm. Gzip provides
 143           a good balance between compression ratio and decompression speed and
 144           has a reasonable compression speed. It is also more likely to be
 145           supported by your build system as the gzip tool is present by default
 146           on most distros.
 147
 148 config INITRAMFS_COMPRESSION_BZIP2
 149         bool "Bzip2"
 150         depends on RD_BZIP2
 151         help
 152           It's compression ratio and speed is intermediate. Decompression speed
 153           is slowest among the choices. The initramfs size is about 10% smaller
 154           with bzip2, in comparison to gzip. Bzip2 uses a large amount of
 155           memory. For modern kernels you will need at least 8MB RAM or more for
 156           booting.
 157
 158           If you choose this, keep in mind that you need to have the bzip2 tool
 159           available to be able to compress the initram.
 160
 161 config INITRAMFS_COMPRESSION_LZMA
 162         bool "LZMA"
 163         depends on RD_LZMA
 164         help
 165           This algorithm's compression ratio is best but has a large dictionary
 166           size which might cause issues in memory constrained systems.
 167           Decompression speed is between the other choices. Compression is
 168           slowest. The initramfs size is about 33% smaller with LZMA in
 169           comparison to gzip.
 170
 171           If you choose this, keep in mind that you may need to install the xz
 172           or lzma tools to be able to compress the initram.
 173
 174 config INITRAMFS_COMPRESSION_XZ
 175         bool "XZ"
 176         depends on RD_XZ
 177         help
 178           XZ uses the LZMA2 algorithm and has a large dictionary which may cause
 179           problems on memory constrained systems. The initramfs size is about
 180           30% smaller with XZ in comparison to gzip. Decompression speed is
 181           better than that of bzip2 but worse than gzip and LZO. Compression is
 182           slow.
 183
 184           If you choose this, keep in mind that you may need to install the xz
 185           tool to be able to compress the initram.
 186
 187 config INITRAMFS_COMPRESSION_LZO
 188         bool "LZO"
 189         depends on RD_LZO
 190         help
 191           It's compression ratio is the second poorest amongst the choices. The
 192           kernel size is about 10% bigger than gzip. Despite that, it's
 193           decompression speed is the second fastest and it's compression speed
 194           is quite fast too.
 195
 196           If you choose this, keep in mind that you may need to install the lzop
 197           tool to be able to compress the initram.
 198
 199 config INITRAMFS_COMPRESSION_LZ4
 200         bool "LZ4"
 201         depends on RD_LZ4
 202         help
 203           It's compression ratio is the poorest amongst the choices. The kernel
 204           size is about 15% bigger than gzip; however its decompression speed
 205           is the fastest.
 206
 207           If you choose this, keep in mind that most distros don't provide lz4
 208           by default which could cause a build failure.
 209
 210 endchoice