bzip2/lzma: config and initramfs support for bzip2/lzma decompression

Impact: New code for initramfs decompression, new features

This is the second part of the bzip2/lzma patch

The bzip patch is based on an idea by Christian Ludwig, includes support for
compressing the kernel with bzip2 or lzma rather than gzip. Both
compressors give smaller sizes than gzip.  Lzma's decompresses faster
than bzip2.

It also supports ramdisks and initramfs' compressed using these two
compressors.

The functionality has been successfully used for a couple of years by
the udpcast project

This version applies to "tip" kernel 2.6.28

This part contains:
- support for new compressions (bzip2 and lzma) in initramfs and
old-style ramdisk
- config dialog for kernel compression (but new kernel compressions
not yet supported)

Signed-off-by: Alain Knaff <alain@knaff.lu>
Signed-off-by: H. Peter Anvin <hpa@zytor.com>

1 files changed, 50 insertions, 0 deletions

diff --git a/init/Kconfig b/init/Kconfig
index f6281711166..df84625b137 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -101,6 +101,56 @@ config LOCALVERSION_AUTO
 
 	  which is done within the script "scripts/setlocalversion".)
 
+choice
+        prompt "Kernel compression mode"
+        default KERNEL_GZIP
+        help
+	  The linux kernel is a kind of self-extracting executable.
+	  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
+	  kernels, mail me (Alain Knaff) <alain@knaff.lu>. (An older
+	  version of this functionality (bzip2 only), for 2.4, was
+	  supplied by Christian Ludwig)
+
+	  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 KERNEL_GZIP
+       bool "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 KERNEL_BZIP2
+	bool "Bzip2"
+	help
+	  Its compression ratio and speed is intermediate.
+	  Decompression speed is slowest among the 3.
+	  The kernel size is about 10 per cent 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 KERNEL_LZMA
+       bool "LZMA"
+       help
+         The most recent compression algorithm.
+	 Its ratio is best, decompression speed is between the other
+	 2. Compression is slowest.
+	 The kernel size is about 33 per cent smaller with lzma,
+	 in comparison to gzip.
+
+endchoice
+
+
 config SWAP
 	bool "Support for paging of anonymous memory (swap)"
 	depends on MMU && BLOCK