2 files changed, 68 insertions, 12 deletions

diff --git a/usr/Kconfig b/usr/Kconfig
index a691a8f5898b..43a3a0fe8f29 100644
--- a/usr/Kconfig
+++ b/usr/Kconfig
@@ -71,3 +71,65 @@ config RD_LZMA
         help
           Support loading of a lzma encoded initial ramdisk or cpio buffer
           If unsure, say N.
+
+choice
+        prompt "Built-in initramfs compression mode"
+        help
+          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) <alain@knaff.lu>.
+
+          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'
+
+config INITRAMFS_COMPRESSION_NONE
+        bool "None"
+        help
+          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
+
+config INITRAMFS_COMPRESSION_GZIP
+        bool "Gzip"
+        depends on RD_GZIP
+        help
+          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.
+
+config INITRAMFS_COMPRESSION_BZIP2
+        bool "Bzip2"
+        depends on RD_BZIP2
+        help
+          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.
+
+config INITRAMFS_COMPRESSION_LZMA
+        bool "LZMA"
+        depends on RD_LZMA
+        help
+          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.
+
+endchoice
diff --git a/usr/Makefile b/usr/Makefile
index 451cdff7dff9..b84894b3929d 100644
--- a/usr/Makefile
+++ b/usr/Makefile
@@ -5,24 +5,18 @@
 klibcdirs:;
 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_$(CONFIG_RD_LZMA)   = .lzma
+# No compression
+suffix_$(CONFIG_INITRAMFS_COMPRESSION_NONE)   =
 
 # Gzip, but no bzip2
-suffix_$(CONFIG_RD_GZIP)   = .gz
+suffix_$(CONFIG_INITRAMFS_COMPRESSION_GZIP)   = .gz
 
 # Bzip2
-suffix_$(CONFIG_RD_BZIP2)  = .bz2
+suffix_$(CONFIG_INITRAMFS_COMPRESSION_BZIP2)  = .bz2
 
+# Lzma
+suffix_$(CONFIG_INITRAMFS_COMPRESSION_LZMA)   = .lzma
 
 # Generate builtin.o based on initramfs_data.o
 obj-$(CONFIG_BLK_DEV_INITRD) := initramfs_data$(suffix_y).o