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 103choice 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 127config INITRAMFS_COMPRESSION_GZIP 128 bool "Gzip" 129 depends on RD_GZIP 130 help 131 Use the old and well tested gzip compression algorithm. Gzip provides 132 a good balance between compression ratio and decompression speed and 133 has a reasonable compression speed. It is also more likely to be 134 supported by your build system as the gzip tool is present by default 135 on most distros. 136 137config INITRAMFS_COMPRESSION_BZIP2 138 bool "Bzip2" 139 depends on RD_BZIP2 140 help 141 It's compression ratio and speed is intermediate. Decompression speed 142 is slowest among the choices. The initramfs size is about 10% smaller 143 with bzip2, in comparison to gzip. Bzip2 uses a large amount of 144 memory. For modern kernels you will need at least 8MB RAM or more for 145 booting. 146 147 If you choose this, keep in mind that you need to have the bzip2 tool 148 available to be able to compress the initram. 149 150config INITRAMFS_COMPRESSION_LZMA 151 bool "LZMA" 152 depends on RD_LZMA 153 help 154 This algorithm's compression ratio is best but has a large dictionary 155 size which might cause issues in memory constrained systems. 156 Decompression speed is between the other choices. Compression is 157 slowest. The initramfs size is about 33% smaller with LZMA in 158 comparison to gzip. 159 160 If you choose this, keep in mind that you may need to install the xz 161 or lzma tools to be able to compress the initram. 162 163config INITRAMFS_COMPRESSION_XZ 164 bool "XZ" 165 depends on RD_XZ 166 help 167 XZ uses the LZMA2 algorithm and has a large dictionary which may cause 168 problems on memory constrained systems. The initramfs size is about 169 30% smaller with XZ in comparison to gzip. Decompression speed is 170 better than that of bzip2 but worse than gzip and LZO. Compression is 171 slow. 172 173 If you choose this, keep in mind that you may need to install the xz 174 tool to be able to compress the initram. 175 176config INITRAMFS_COMPRESSION_LZO 177 bool "LZO" 178 depends on RD_LZO 179 help 180 It's compression ratio is the second poorest amongst the choices. The 181 kernel size is about 10% bigger than gzip. Despite that, it's 182 decompression speed is the second fastest and it's compression speed 183 is quite fast too. 184 185 If you choose this, keep in mind that you may need to install the lzop 186 tool to be able to compress the initram. 187 188config INITRAMFS_COMPRESSION_LZ4 189 bool "LZ4" 190 depends on RD_LZ4 191 help 192 It's compression ratio is the poorest amongst the choices. The kernel 193 size is about 15% bigger than gzip; however its decompression speed 194 is the fastest. 195 196 If you choose this, keep in mind that most distros don't provide lz4 197 by default which could cause a build failure. 198 199config INITRAMFS_COMPRESSION_NONE 200 bool "None" 201 help 202 Do not compress the built-in initramfs at all. This may sound wasteful 203 in space, but, you should be aware that the built-in initramfs will be 204 compressed at a later stage anyways along with the rest of the kernel, 205 on those architectures that support this. However, not compressing the 206 initramfs may lead to slightly higher memory consumption during a 207 short time at boot, while both the cpio image and the unpacked 208 filesystem image will be present in memory simultaneously 209 210endchoice 211