decompressors: add XZ decompressor module

In userspace, the .lzma format has become mostly a legacy file format that
got superseded by the .xz format.  Similarly, LZMA Utils was superseded by
XZ Utils.

These patches add support for XZ decompression into the kernel.  Most of
the code is as is from XZ Embedded <http://tukaani.org/xz/embedded.html>.
It was written for the Linux kernel but is usable in other projects too.

Advantages of XZ over the current LZMA code in the kernel:
  - Nice API that can be used by other kernel modules; it's
    not limited to kernel, initramfs, and initrd decompression.
  - Integrity check support (CRC32)
  - BCJ filters improve compression of executable code on
    certain architectures. These together with LZMA2 can
    produce a few percent smaller kernel or Squashfs images
    than plain LZMA without making the decompression slower.

This patch: Add the main decompression code (xz_dec), testing module
(xz_dec_test), wrapper script (xz_wrap.sh) for the xz command line tool,
and documentation.  The xz_dec module is enough to have a usable XZ
decompressor e.g.  for Squashfs.

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, 59 insertions, 0 deletions

diff --git a/lib/xz/Kconfig b/lib/xz/Kconfig
new file mode 100644
index 00000000000..e3b6e18fdac
--- /dev/null
+++ b/lib/xz/Kconfig
@@ -0,0 +1,59 @@
+config XZ_DEC
+	tristate "XZ decompression support"
+	select CRC32
+	help
+	  LZMA2 compression algorithm and BCJ filters are supported using
+	  the .xz file format as the container. For integrity checking,
+	  CRC32 is supported. See Documentation/xz.txt for more information.
+
+config XZ_DEC_X86
+	bool "x86 BCJ filter decoder" if EMBEDDED
+	default y
+	depends on XZ_DEC
+	select XZ_DEC_BCJ
+
+config XZ_DEC_POWERPC
+	bool "PowerPC BCJ filter decoder" if EMBEDDED
+	default y
+	depends on XZ_DEC
+	select XZ_DEC_BCJ
+
+config XZ_DEC_IA64
+	bool "IA-64 BCJ filter decoder" if EMBEDDED
+	default y
+	depends on XZ_DEC
+	select XZ_DEC_BCJ
+
+config XZ_DEC_ARM
+	bool "ARM BCJ filter decoder" if EMBEDDED
+	default y
+	depends on XZ_DEC
+	select XZ_DEC_BCJ
+
+config XZ_DEC_ARMTHUMB
+	bool "ARM-Thumb BCJ filter decoder" if EMBEDDED
+	default y
+	depends on XZ_DEC
+	select XZ_DEC_BCJ
+
+config XZ_DEC_SPARC
+	bool "SPARC BCJ filter decoder" if EMBEDDED
+	default y
+	depends on XZ_DEC
+	select XZ_DEC_BCJ
+
+config XZ_DEC_BCJ
+	bool
+	default n
+
+config XZ_DEC_TEST
+	tristate "XZ decompressor tester"
+	default n
+	depends on XZ_DEC
+	help
+	  This allows passing .xz files to the in-kernel XZ decoder via
+	  a character special file. It calculates CRC32 of the decompressed
+	  data and writes diagnostics to the system log.
+
+	  Unless you are developing the XZ decoder, you don't need this
+	  and should say N.