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