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>
diff --git a/fs/squashfs/xz_wrapper.c b/fs/squashfs/xz_wrapper.c
index 397adea..06d0d11 100644
--- a/fs/squashfs/xz_wrapper.c
+++ b/fs/squashfs/xz_wrapper.c
@@ -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 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);
}