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, 18 insertions, 0 deletions

diff --git a/usr/Kconfig b/usr/Kconfig
index c2c7fe2f717d..4780deac5974 100644
--- a/usr/Kconfig
+++ b/usr/Kconfig
@@ -72,6 +72,15 @@ config RD_LZMA
           Support loading of a LZMA encoded initial ramdisk or cpio buffer
           If unsure, say N.
 
+config RD_XZ
+        bool "Support initial ramdisks compressed using XZ" if EMBEDDED
+        default !EMBEDDED
+        depends on BLK_DEV_INITRD
+        select DECOMPRESS_XZ
+        help
+          Support loading of a XZ encoded initial ramdisk or cpio buffer.
+          If unsure, say N.
+
 config RD_LZO
         bool "Support initial ramdisks compressed using LZO" if EMBEDDED
         default !EMBEDDED
@@ -139,6 +148,15 @@ config INITRAMFS_COMPRESSION_LZMA
           three. Compression is slowest. The initramfs size is about 33%
           smaller with LZMA in comparison to gzip.
 
+config INITRAMFS_COMPRESSION_XZ
+        bool "XZ"
+        depends on RD_XZ
+        help
+          XZ uses the LZMA2 algorithm. The initramfs size is about 30%
+          smaller with XZ in comparison to gzip. Decompression speed
+          is better than that of bzip2 but worse than gzip and LZO.
+          Compression is slow.
+
 config INITRAMFS_COMPRESSION_LZO
         bool "LZO"
         depends on RD_LZO