decompressors: add boot-time XZ support

This implements the API defined in <linux/decompress/generic.h> which is
used for kernel, initramfs, and initrd decompression.  This patch together
with the first patch is enough for XZ-compressed initramfs and initrd;
XZ-compressed kernel will need arch-specific changes.

The buffering requirements described in decompress_unxz.c are stricter
than with gzip, so the relevant changes should be done to the
arch-specific code when adding support for XZ-compressed kernel.
Similarly, the heap size in arch-specific pre-boot code may need to be
increased (30 KiB is enough).

The XZ decompressor needs memmove(), memeq() (memcmp() == 0), and
memzero() (memset(ptr, 0, size)), which aren't available in all
arch-specific pre-boot environments.  I'm including simple versions in
decompress_unxz.c, but a cleaner solution would naturally be nicer.

Signed-off-by: Lasse Collin <lasse.collin@tukaani.org>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Alain Knaff <alain@knaff.lu>
Cc: Albin Tonnerre <albin.tonnerre@free-electrons.com>
Cc: Phillip Lougher <phillip@lougher.demon.co.uk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 19 insertions, 1 deletions

diff --git a/init/Kconfig b/init/Kconfig
index 8dfd094e6875..ea176e8edbdd 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -130,13 +130,16 @@ config HAVE_KERNEL_BZIP2
 config HAVE_KERNEL_LZMA
         bool
 
+config HAVE_KERNEL_XZ
+        bool
+
 config HAVE_KERNEL_LZO
         bool
 
 choice
         prompt "Kernel compression mode"
         default KERNEL_GZIP
-        depends on HAVE_KERNEL_GZIP || HAVE_KERNEL_BZIP2 || HAVE_KERNEL_LZMA || HAVE_KERNEL_LZO
+        depends on HAVE_KERNEL_GZIP || HAVE_KERNEL_BZIP2 || HAVE_KERNEL_LZMA || HAVE_KERNEL_XZ || HAVE_KERNEL_LZO
         help
           The linux kernel is a kind of self-extracting executable.
           Several compression algorithms are available, which differ
@@ -181,6 +184,21 @@ config KERNEL_LZMA
           two. Compression is slowest.  The kernel size is about 33%
           smaller with LZMA in comparison to gzip.
 
+config KERNEL_XZ
+        bool "XZ"
+        depends on HAVE_KERNEL_XZ
+        help
+          XZ uses the LZMA2 algorithm and instruction set specific
+          BCJ filters which can improve compression ratio of executable
+          code. The size of the kernel is about 30% smaller with XZ in
+          comparison to gzip. On architectures for which there is a BCJ
+          filter (i386, x86_64, ARM, IA-64, PowerPC, and SPARC), XZ
+          will create a few percent smaller kernel than plain LZMA.
+
+          The speed is about the same as with LZMA: The decompression
+          speed of XZ is better than that of bzip2 but worse than gzip
+          and LZO. Compression is slow.
+
 config KERNEL_LZO
         bool "LZO"
         depends on HAVE_KERNEL_LZO