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 config RD_ZSTD
 104         bool "Support initial ramdisk/ramfs compressed using ZSTD"
 105         default y
 106         select DECOMPRESS_ZSTD
 107         help
 108           Support loading of a ZSTD encoded initial ramdisk or cpio buffer.
 109           If unsure, say N.
 110
 111 choice
 112         prompt "Built-in initramfs compression mode"
 113         depends on INITRAMFS_SOURCE != ""
 114         help
 115           This option allows you to decide by which algorithm the builtin
 116           initramfs will be compressed.  Several compression algorithms are
 117           available, which differ in efficiency, compression and
 118           decompression speed.  Compression speed is only relevant
 119           when building a kernel.  Decompression speed is relevant at
 120           each boot. Also the memory usage during decompression may become
 121           relevant on memory constrained systems. This is usually based on the
 122           dictionary size of the algorithm with algorithms like XZ and LZMA
 123           featuring large dictionary sizes.
 124
 125           High compression options are mostly useful for users who are
 126           low on RAM, since it reduces the memory consumption during
 127           boot.
 128
 129           Keep in mind that your build system needs to provide the appropriate
 130           compression tool to compress the generated initram cpio file for
 131           embedding.
 132
 133           If in doubt, select 'None'
 134
 135 config INITRAMFS_COMPRESSION_GZIP
 136         bool "Gzip"
 137         depends on RD_GZIP
 138         help
 139           Use the old and well tested gzip compression algorithm. Gzip provides
 140           a good balance between compression ratio and decompression speed and
 141           has a reasonable compression speed. It is also more likely to be
 142           supported by your build system as the gzip tool is present by default
 143           on most distros.
 144
 145 config INITRAMFS_COMPRESSION_BZIP2
 146         bool "Bzip2"
 147         depends on RD_BZIP2
 148         help
 149           It's compression ratio and speed is intermediate. Decompression speed
 150           is slowest among the choices. The initramfs size is about 10% smaller
 151           with bzip2, in comparison to gzip. Bzip2 uses a large amount of
 152           memory. For modern kernels you will need at least 8MB RAM or more for
 153           booting.
 154
 155           If you choose this, keep in mind that you need to have the bzip2 tool
 156           available to be able to compress the initram.
 157
 158 config INITRAMFS_COMPRESSION_LZMA
 159         bool "LZMA"
 160         depends on RD_LZMA
 161         help
 162           This algorithm's compression ratio is best but has a large dictionary
 163           size which might cause issues in memory constrained systems.
 164           Decompression speed is between the other choices. Compression is
 165           slowest. The initramfs size is about 33% smaller with LZMA in
 166           comparison to gzip.
 167
 168           If you choose this, keep in mind that you may need to install the xz
 169           or lzma tools to be able to compress the initram.
 170
 171 config INITRAMFS_COMPRESSION_XZ
 172         bool "XZ"
 173         depends on RD_XZ
 174         help
 175           XZ uses the LZMA2 algorithm and has a large dictionary which may cause
 176           problems on memory constrained systems. The initramfs size is about
 177           30% smaller with XZ in comparison to gzip. Decompression speed is
 178           better than that of bzip2 but worse than gzip and LZO. Compression is
 179           slow.
 180
 181           If you choose this, keep in mind that you may need to install the xz
 182           tool to be able to compress the initram.
 183
 184 config INITRAMFS_COMPRESSION_LZO
 185         bool "LZO"
 186         depends on RD_LZO
 187         help
 188           Its compression ratio is the second poorest amongst the choices. The
 189           kernel size is about 10% bigger than gzip. Despite that, its
 190           decompression speed is the second fastest and its compression speed
 191           is quite fast too.
 192
 193           If you choose this, keep in mind that you may need to install the lzop
 194           tool to be able to compress the initram.
 195
 196 config INITRAMFS_COMPRESSION_LZ4
 197         bool "LZ4"
 198         depends on RD_LZ4
 199         help
 200           It's compression ratio is the poorest amongst the choices. The kernel
 201           size is about 15% bigger than gzip; however its decompression speed
 202           is the fastest.
 203
 204           If you choose this, keep in mind that most distros don't provide lz4
 205           by default which could cause a build failure.
 206
 207 config INITRAMFS_COMPRESSION_ZSTD
 208         bool "ZSTD"
 209         depends on RD_ZSTD
 210         help
 211           ZSTD is a compression algorithm targeting intermediate compression
 212           with fast decompression speed. It will compress better than GZIP and
 213           decompress around the same speed as LZO, but slower than LZ4.
 214
 215           If you choose this, keep in mind that you may need to install the zstd
 216           tool to be able to compress the initram.
 217
 218 config INITRAMFS_COMPRESSION_NONE
 219         bool "None"
 220         help
 221           Do not compress the built-in initramfs at all. This may sound wasteful
 222           in space, but, you should be aware that the built-in initramfs will be
 223           compressed at a later stage anyways along with the rest of the kernel,
 224           on those architectures that support this. However, not compressing the
 225           initramfs may lead to slightly higher memory consumption during a
 226           short time at boot, while both the cpio image and the unpacked
 227           filesystem image will be present in memory simultaneously
 228
 229 endchoice