Commit ab76f3d7 authored by Alain Knaff's avatar Alain Knaff Committed by H. Peter Anvin

bzip2/lzma: make internal initramfs compression configurable

Impact: Avoids silent environment dependency

Make builtin initramfs compression an explicit configurable.  The
previous version would pick a compression based on the binaries which
were installed on the system, which could lead to unexpected results.
It is now explicitly configured, and not having the appropriate
binaries installed on the build host is simply an error.
Signed-off-by: default avatarAlain Knaff <>
Signed-off-by: default avatarH. Peter Anvin <>
parent ab59d3b7
......@@ -71,3 +71,65 @@ config RD_LZMA
Support loading of a lzma encoded initial ramdisk or cpio buffer
If unsure, say N.
prompt "Built-in initramfs compression mode"
This setting is only meaningful if the INITRAMFS_SOURCE is
set. It decides by which algorithm the INITRAMFS_SOURCE will
be compressed.
Several compression algorithms are available, which differ
in efficiency, compression and decompression speed.
Compression speed is only relevant when building a kernel.
Decompression speed is relevant at each boot.
If you have any problems with bzip2 or lzma compressed
initramfs, mail me (Alain Knaff) <>.
High compression options are mostly useful for users who
are low on disk space (embedded systems), but for whom ram
size matters less.
If in doubt, select 'gzip'
bool "None"
Do not compress the built-in initramfs at all. This may
sound wasteful in space, but, you should be aware that the
built-in initramfs will be compressed at a later stage
anyways along with the rest of the kernel, on those
architectures that support this.
However, not compressing the initramfs may lead to slightly
higher memory consumption during a short time at boot, while
both the cpio image and the unpacked filesystem image will
be present in memory simultaneously
bool "Gzip"
depends on RD_GZIP
The old and tried gzip compression. Its compression ratio is
the poorest among the 3 choices; however its speed (both
compression and decompression) is the fastest.
bool "Bzip2"
depends on RD_BZIP2
Its compression ratio and speed is intermediate.
Decompression speed is slowest among the three. The initramfs
size is about 10% smaller with bzip2, in comparison to gzip.
Bzip2 uses a large amount of memory. For modern kernels you
will need at least 8MB RAM or more for booting.
bool "LZMA"
depends on RD_LZMA
The most recent compression algorithm.
Its ratio is best, decompression speed is between the other
two. Compression is slowest. The initramfs size is about 33%
smaller with LZMA in comparison to gzip.
......@@ -5,24 +5,18 @@
PHONY += klibcdirs
# Find out "preferred" ramdisk compressor. Order of preference is
# 1. bzip2 efficient, and likely to be present
# 2. gzip former default
# 3. lzma
# 4. none
# None of the above
suffix_y =
# Lzma, but no gzip nor bzip2
suffix_$(CONFIG_RD_LZMA) = .lzma
# No compression
# Gzip, but no bzip2
suffix_$(CONFIG_RD_GZIP) = .gz
# Bzip2
suffix_$(CONFIG_RD_BZIP2) = .bz2
# Lzma
# Generate builtin.o based on initramfs_data.o
obj-$(CONFIG_BLK_DEV_INITRD) := initramfs_data$(suffix_y).o
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