Squashfs: add compression options support to xz decompressor
Phillip Lougher [Mon, 28 Feb 2011 15:31:46 +0000 (15:31 +0000)]
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>

fs/squashfs/xz_wrapper.c

index 397adea..06d0d11 100644 (file)
@@ -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;
+
+       if (comp_opts) {
+               /* check compressor options are the expected length */
+               if (len < sizeof(*comp_opts)) {
+                       err = -EIO;
+                       goto failed;
+               }
 
-       struct squashfs_xz *stream = kmalloc(sizeof(*stream), GFP_KERNEL);
-       if (stream == 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, block_size);
-       if (stream->state == NULL)
+       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);
 }