1# SPDX-License-Identifier: GPL-2.0 2# 3# Configuration for initramfs 4# 5 6config 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 25config 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 35config 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 45config 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 55config 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 63config 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 71config 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 79config 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 87config 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 95config 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 103config 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 111choice 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 135config 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 145config 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 158config 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 171config 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 184config 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 196config 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 207config 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 218config 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 229endchoice 230