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Squashfs: add compression options support to xz decompressor 

Pass the dictionary size used to compress datablocks.  Using a
dictionary size less than the block size saves memory overhead, in many
cases without adversely affecting compression ratio.

Signed-off-by: Phillip Lougher <phillip@lougher.demon.co.uk>
This commit is contained in:
Phillip Lougher 2011-02-28 15:31:46 +00:00
parent b7fc0ff09d
commit ff750311d3
1 changed files with 42 additions and 9 deletions
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51
fs/squashfs/xz_wrapper.c
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@ -26,6 +26,7 @@
#include <linux/buffer_head.h>
#include <linux/slab.h>
#include <linux/xz.h>
#include <linux/bitops.h>
#include "squashfs_fs.h"
#include "squashfs_fs_sb.h"
@ -38,25 +39,57 @@ struct squashfs_xz {
struct xz_buf buf;
};
struct comp_opts {
__le32 dictionary_size;
__le32 flags;
};
static void *squashfs_xz_init(struct squashfs_sb_info *msblk, void *buff,
int len)
{
int block_size = max_t(int, msblk->block_size, SQUASHFS_METADATA_SIZE);
struct comp_opts *comp_opts = buff;
struct squashfs_xz *stream;
int dict_size = msblk->block_size;
int err, n;
struct squashfs_xz *stream = kmalloc(sizeof(*stream), GFP_KERNEL);
if (stream == NULL)
goto failed;
if (comp_opts) {
/* check compressor options are the expected length */
if (len < sizeof(*comp_opts)) {
err = -EIO;
goto failed;
}
stream->state = xz_dec_init(XZ_PREALLOC, block_size);
if (stream->state == NULL)
dict_size = le32_to_cpu(comp_opts->dictionary_size);
/* the dictionary size should be 2^n or 2^n+2^(n+1) */
n = ffs(dict_size) - 1;
if (dict_size != (1 << n) && dict_size != (1 << n) +
(1 << (n + 1))) {
err = -EIO;
goto failed;
}
}
dict_size = max_t(int, dict_size, SQUASHFS_METADATA_SIZE);
stream = kmalloc(sizeof(*stream), GFP_KERNEL);
if (stream == NULL) {
err = -ENOMEM;
goto failed;
}
stream->state = xz_dec_init(XZ_PREALLOC, dict_size);
if (stream->state == NULL) {
kfree(stream);
err = -ENOMEM;
goto failed;
}
return stream;
failed:
ERROR("Failed to allocate xz workspace\n");
kfree(stream);
return ERR_PTR(-ENOMEM);
ERROR("Failed to initialise xz decompressor\n");
return ERR_PTR(err);
}