*
  * total_out is the last byte of the buffer
  */
-int btrfs_decompress_buf2page(char *buf, unsigned long buf_start,
+int btrfs_decompress_buf2page(const char *buf, unsigned long buf_start,
                              unsigned long total_out, u64 disk_start,
                              struct bio *bio)
 {
 
                         unsigned long max_out);
 int btrfs_decompress(int type, unsigned char *data_in, struct page *dest_page,
                     unsigned long start_byte, size_t srclen, size_t destlen);
-int btrfs_decompress_buf2page(char *buf, unsigned long buf_start,
+int btrfs_decompress_buf2page(const char *buf, unsigned long buf_start,
                              unsigned long total_out, u64 disk_start,
                              struct bio *bio);
 
 
        memcpy(buf, &dlen, LZO_LEN);
 }
 
-static inline size_t read_compress_length(char *buf)
+static inline size_t read_compress_length(const char *buf)
 {
        __le32 dlen;