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 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 112choice 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 136config 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 146config 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 159config 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 172config 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 185config 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 197config 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 208config 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 219config 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 230endchoice 231