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decompressors: add boot-time XZ support

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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>
This commit is contained in:
Lasse Collin 2011-01-12 17:01:23 -08:00 committed by Linus Torvalds
parent 24fa0402a9
commit 3ebe12439b
9 changed files with 469 additions and 2 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

19
include/linux/decompress/unxz.h Normal file
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@ -0,0 +1,19 @@
/*
* Wrapper for decompressing XZ-compressed kernel, initramfs, and initrd
*
* Author: Lasse Collin <lasse.collin@tukaani.org>
*
* This file has been put into the public domain.
* You can do whatever you want with this file.
*/
#ifndef DECOMPRESS_UNXZ_H
#define DECOMPRESS_UNXZ_H
int unxz(unsigned char *in, int in_size,
int (*fill)(void *dest, unsigned int size),
int (*flush)(void *src, unsigned int size),
unsigned char *out, int *in_used,
void (*error)(char *x));
#endif

20
init/Kconfig
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@ -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

4
lib/Kconfig
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@ -122,6 +122,10 @@ config DECOMPRESS_BZIP2
config DECOMPRESS_LZMA
tristate
config DECOMPRESS_XZ
select XZ_DEC
tristate
config DECOMPRESS_LZO
select LZO_DECOMPRESS
tristate

1
lib/Makefile
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@ -75,6 +75,7 @@ obj-$(CONFIG_RAID6_PQ) += raid6/
lib-$(CONFIG_DECOMPRESS_GZIP) += decompress_inflate.o
lib-$(CONFIG_DECOMPRESS_BZIP2) += decompress_bunzip2.o
lib-$(CONFIG_DECOMPRESS_LZMA) += decompress_unlzma.o
lib-$(CONFIG_DECOMPRESS_XZ) += decompress_unxz.o
lib-$(CONFIG_DECOMPRESS_LZO) += decompress_unlzo.o
obj-$(CONFIG_TEXTSEARCH) += textsearch.o

5
lib/decompress.c
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@ -8,6 +8,7 @@
#include <linux/decompress/bunzip2.h>
#include <linux/decompress/unlzma.h>
#include <linux/decompress/unxz.h>
#include <linux/decompress/inflate.h>
#include <linux/decompress/unlzo.h>
@ -23,6 +24,9 @@
#ifndef CONFIG_DECOMPRESS_LZMA
# define unlzma NULL
#endif
#ifndef CONFIG_DECOMPRESS_XZ
# define unxz NULL
#endif
#ifndef CONFIG_DECOMPRESS_LZO
# define unlzo NULL
#endif
@ -36,6 +40,7 @@ static const struct compress_format {
{ {037, 0236}, "gzip", gunzip },
{ {0x42, 0x5a}, "bzip2", bunzip2 },
{ {0x5d, 0x00}, "lzma", unlzma },
{ {0xfd, 0x37}, "xz", unxz },
{ {0x89, 0x4c}, "lzo", unlzo },
{ {0, 0}, NULL, NULL }
};

397
lib/decompress_unxz.c Normal file
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@ -0,0 +1,397 @@
/*
* Wrapper for decompressing XZ-compressed kernel, initramfs, and initrd
*
* Author: Lasse Collin <lasse.collin@tukaani.org>
*
* This file has been put into the public domain.
* You can do whatever you want with this file.
*/
/*
* Important notes about in-place decompression
*
* At least on x86, the kernel is decompressed in place: the compressed data
* is placed to the end of the output buffer, and the decompressor overwrites
* most of the compressed data. There must be enough safety margin to
* guarantee that the write position is always behind the read position.
*
* The safety margin for XZ with LZMA2 or BCJ+LZMA2 is calculated below.
* Note that the margin with XZ is bigger than with Deflate (gzip)!
*
* The worst case for in-place decompression is that the beginning of
* the file is compressed extremely well, and the rest of the file is
* uncompressible. Thus, we must look for worst-case expansion when the
* compressor is encoding uncompressible data.
*
* The structure of the .xz file in case of a compresed kernel is as follows.
* Sizes (as bytes) of the fields are in parenthesis.
*
* Stream Header (12)
* Block Header:
* Block Header (8-12)
* Compressed Data (N)
* Block Padding (0-3)
* CRC32 (4)
* Index (8-20)
* Stream Footer (12)
*
* Normally there is exactly one Block, but let's assume that there are
* 2-4 Blocks just in case. Because Stream Header and also Block Header
* of the first Block don't make the decompressor produce any uncompressed
* data, we can ignore them from our calculations. Block Headers of possible
* additional Blocks have to be taken into account still. With these
* assumptions, it is safe to assume that the total header overhead is
* less than 128 bytes.
*
* Compressed Data contains LZMA2 or BCJ+LZMA2 encoded data. Since BCJ
* doesn't change the size of the data, it is enough to calculate the
* safety margin for LZMA2.
*
* LZMA2 stores the data in chunks. Each chunk has a header whose size is
* a maximum of 6 bytes, but to get round 2^n numbers, let's assume that
* the maximum chunk header size is 8 bytes. After the chunk header, there
* may be up to 64 KiB of actual payload in the chunk. Often the payload is
* quite a bit smaller though; to be safe, let's assume that an average
* chunk has only 32 KiB of payload.
*
* The maximum uncompressed size of the payload is 2 MiB. The minimum
* uncompressed size of the payload is in practice never less than the
* payload size itself. The LZMA2 format would allow uncompressed size
* to be less than the payload size, but no sane compressor creates such
* files. LZMA2 supports storing uncompressible data in uncompressed form,
* so there's never a need to create payloads whose uncompressed size is
* smaller than the compressed size.
*
* The assumption, that the uncompressed size of the payload is never
* smaller than the payload itself, is valid only when talking about
* the payload as a whole. It is possible that the payload has parts where
* the decompressor consumes more input than it produces output. Calculating
* the worst case for this would be tricky. Instead of trying to do that,
* let's simply make sure that the decompressor never overwrites any bytes
* of the payload which it is currently reading.
*
* Now we have enough information to calculate the safety margin. We need
* - 128 bytes for the .xz file format headers;
* - 8 bytes per every 32 KiB of uncompressed size (one LZMA2 chunk header
* per chunk, each chunk having average payload size of 32 KiB); and
* - 64 KiB (biggest possible LZMA2 chunk payload size) to make sure that
* the decompressor never overwrites anything from the LZMA2 chunk
* payload it is currently reading.
*
* We get the following formula:
*
* safety_margin = 128 + uncompressed_size * 8 / 32768 + 65536
* = 128 + (uncompressed_size >> 12) + 65536
*
* For comparision, according to arch/x86/boot/compressed/misc.c, the
* equivalent formula for Deflate is this:
*
* safety_margin = 18 + (uncompressed_size >> 12) + 32768
*
* Thus, when updating Deflate-only in-place kernel decompressor to
* support XZ, the fixed overhead has to be increased from 18+32768 bytes
* to 128+65536 bytes.
*/
/*
* STATIC is defined to "static" if we are being built for kernel
* decompression (pre-boot code). <linux/decompress/mm.h> will define
* STATIC to empty if it wasn't already defined. Since we will need to
* know later if we are being used for kernel decompression, we define
* XZ_PREBOOT here.
*/
#ifdef STATIC
# define XZ_PREBOOT
#endif
#ifdef __KERNEL__
# include <linux/decompress/mm.h>
#endif
#define XZ_EXTERN STATIC
#ifndef XZ_PREBOOT
# include <linux/slab.h>
# include <linux/xz.h>
#else
/*
* Use the internal CRC32 code instead of kernel's CRC32 module, which
* is not available in early phase of booting.
*/
#define XZ_INTERNAL_CRC32 1
/*
* For boot time use, we enable only the BCJ filter of the current
* architecture or none if no BCJ filter is available for the architecture.
*/
#ifdef CONFIG_X86
# define XZ_DEC_X86
#endif
#ifdef CONFIG_PPC
# define XZ_DEC_POWERPC
#endif
#ifdef CONFIG_ARM
# define XZ_DEC_ARM
#endif
#ifdef CONFIG_IA64
# define XZ_DEC_IA64
#endif
#ifdef CONFIG_SPARC
# define XZ_DEC_SPARC
#endif
/*
* This will get the basic headers so that memeq() and others
* can be defined.
*/
#include "xz/xz_private.h"
/*
* Replace the normal allocation functions with the versions from
* <linux/decompress/mm.h>. vfree() needs to support vfree(NULL)
* when XZ_DYNALLOC is used, but the pre-boot free() doesn't support it.
* Workaround it here because the other decompressors don't need it.
*/
#undef kmalloc
#undef kfree
#undef vmalloc
#undef vfree
#define kmalloc(size, flags) malloc(size)
#define kfree(ptr) free(ptr)
#define vmalloc(size) malloc(size)
#define vfree(ptr) do { if (ptr != NULL) free(ptr); } while (0)
/*
* FIXME: Not all basic memory functions are provided in architecture-specific
* files (yet). We define our own versions here for now, but this should be
* only a temporary solution.
*
* memeq and memzero are not used much and any remotely sane implementation
* is fast enough. memcpy/memmove speed matters in multi-call mode, but
* the kernel image is decompressed in single-call mode, in which only
* memcpy speed can matter and only if there is a lot of uncompressible data
* (LZMA2 stores uncompressible chunks in uncompressed form). Thus, the
* functions below should just be kept small; it's probably not worth
* optimizing for speed.
*/
#ifndef memeq
static bool memeq(const void *a, const void *b, size_t size)
{
const uint8_t *x = a;
const uint8_t *y = b;
size_t i;
for (i = 0; i < size; ++i)
if (x[i] != y[i])
return false;
return true;
}
#endif
#ifndef memzero
static void memzero(void *buf, size_t size)
{
uint8_t *b = buf;
uint8_t *e = b + size;
while (b != e)
*b++ = '\0';
}
#endif
#ifndef memmove
/* Not static to avoid a conflict with the prototype in the Linux headers. */
void *memmove(void *dest, const void *src, size_t size)
{
uint8_t *d = dest;
const uint8_t *s = src;
size_t i;
if (d < s) {
for (i = 0; i < size; ++i)
d[i] = s[i];
} else if (d > s) {
i = size;
while (i-- > 0)
d[i] = s[i];
}
return dest;
}
#endif
/*
* Since we need memmove anyway, would use it as memcpy too.
* Commented out for now to avoid breaking things.
*/
/*
#ifndef memcpy
# define memcpy memmove
#endif
*/
#include "xz/xz_crc32.c"
#include "xz/xz_dec_stream.c"
#include "xz/xz_dec_lzma2.c"
#include "xz/xz_dec_bcj.c"
#endif /* XZ_PREBOOT */
/* Size of the input and output buffers in multi-call mode */
#define XZ_IOBUF_SIZE 4096
/*
* This function implements the API defined in <linux/decompress/generic.h>.
*
* This wrapper will automatically choose single-call or multi-call mode
* of the native XZ decoder API. The single-call mode can be used only when
* both input and output buffers are available as a single chunk, i.e. when
* fill() and flush() won't be used.
*/
STATIC int INIT unxz(unsigned char *in, int in_size,
int (*fill)(void *dest, unsigned int size),
int (*flush)(void *src, unsigned int size),
unsigned char *out, int *in_used,
void (*error)(char *x))
{
struct xz_buf b;
struct xz_dec *s;
enum xz_ret ret;
bool must_free_in = false;
#if XZ_INTERNAL_CRC32
xz_crc32_init();
#endif
if (in_used != NULL)
*in_used = 0;
if (fill == NULL && flush == NULL)
s = xz_dec_init(XZ_SINGLE, 0);
else
s = xz_dec_init(XZ_DYNALLOC, (uint32_t)-1);
if (s == NULL)
goto error_alloc_state;
if (flush == NULL) {
b.out = out;
b.out_size = (size_t)-1;
} else {
b.out_size = XZ_IOBUF_SIZE;
b.out = malloc(XZ_IOBUF_SIZE);
if (b.out == NULL)
goto error_alloc_out;
}
if (in == NULL) {
must_free_in = true;
in = malloc(XZ_IOBUF_SIZE);
if (in == NULL)
goto error_alloc_in;
}
b.in = in;
b.in_pos = 0;
b.in_size = in_size;
b.out_pos = 0;
if (fill == NULL && flush == NULL) {
ret = xz_dec_run(s, &b);
} else {
do {
if (b.in_pos == b.in_size && fill != NULL) {
if (in_used != NULL)
*in_used += b.in_pos;
b.in_pos = 0;
in_size = fill(in, XZ_IOBUF_SIZE);
if (in_size < 0) {
/*
* This isn't an optimal error code
* but it probably isn't worth making
* a new one either.
*/
ret = XZ_BUF_ERROR;
break;
}
b.in_size = in_size;
}
ret = xz_dec_run(s, &b);
if (flush != NULL && (b.out_pos == b.out_size
|| (ret != XZ_OK && b.out_pos > 0))) {
/*
* Setting ret here may hide an error
* returned by xz_dec_run(), but probably
* it's not too bad.
*/
if (flush(b.out, b.out_pos) != (int)b.out_pos)
ret = XZ_BUF_ERROR;
b.out_pos = 0;
}
} while (ret == XZ_OK);
if (must_free_in)
free(in);
if (flush != NULL)
free(b.out);
}
if (in_used != NULL)
*in_used += b.in_pos;
xz_dec_end(s);
switch (ret) {
case XZ_STREAM_END:
return 0;
case XZ_MEM_ERROR:
/* This can occur only in multi-call mode. */
error("XZ decompressor ran out of memory");
break;
case XZ_FORMAT_ERROR:
error("Input is not in the XZ format (wrong magic bytes)");
break;
case XZ_OPTIONS_ERROR:
error("Input was encoded with settings that are not "
"supported by this XZ decoder");
break;
case XZ_DATA_ERROR:
case XZ_BUF_ERROR:
error("XZ-compressed data is corrupt");
break;
default:
error("Bug in the XZ decompressor");
break;
}
return -1;
error_alloc_in:
if (flush != NULL)
free(b.out);
error_alloc_out:
xz_dec_end(s);
error_alloc_state:
error("XZ decompressor ran out of memory");
return -1;
}
/*
* This macro is used by architecture-specific files to decompress
* the kernel image.
*/
#define decompress unxz

2
scripts/gen_initramfs_list.sh
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@ -243,6 +243,8 @@ case "$arg" in
echo "$output_file" | grep -q "\.gz$" && compr="gzip -9 -f"
echo "$output_file" | grep -q "\.bz2$" && compr="bzip2 -9 -f"
echo "$output_file" | grep -q "\.lzma$" && compr="lzma -9 -f"
echo "$output_file" | grep -q "\.xz$" && \
compr="xz --check=crc32 --lzma2=dict=1MiB"
echo "$output_file" | grep -q "\.lzo$" && compr="lzop -9 -f"
echo "$output_file" | grep -q "\.cpio$" && compr="cat"
shift

18
usr/Kconfig
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@ -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

5
usr/Makefile
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@ -15,6 +15,9 @@ suffix_$(CONFIG_INITRAMFS_COMPRESSION_BZIP2) = .bz2
# Lzma
suffix_$(CONFIG_INITRAMFS_COMPRESSION_LZMA) = .lzma
# XZ
suffix_$(CONFIG_INITRAMFS_COMPRESSION_XZ) = .xz
# Lzo
suffix_$(CONFIG_INITRAMFS_COMPRESSION_LZO) = .lzo
@ -50,7 +53,7 @@ endif
quiet_cmd_initfs = GEN $@
cmd_initfs = $(initramfs) -o $@ $(ramfs-args) $(ramfs-input)
targets := initramfs_data.cpio.gz initramfs_data.cpio.bz2 initramfs_data.cpio.lzma initramfs_data.cpio.lzo initramfs_data.cpio
targets := initramfs_data.cpio.gz initramfs_data.cpio.bz2 initramfs_data.cpio.lzma initramfs_data.cpio.xz initramfs_data.cpio.lzo initramfs_data.cpio
# do not try to update files included in initramfs
$(deps_initramfs): ;