7 files changed, 33 insertions, 9 deletions
diff --git a/include/sqfs/block_processor.h b/include/sqfs/block_processor.h
index 2ad12c0..d3b6e12 100644
--- a/include/sqfs/block_processor.h
+++ b/include/sqfs/block_processor.h
@@ -43,6 +43,8 @@
  * Internally it takes care of partitioning data in the correct block sizes,
  * adding tail-ens to fragment blocks, compressing the data, deduplicating data
  * and finally writing it to disk.
+ *
+ * This object is not copyable, i.e. @ref sqfs_copy will always return NULL.
  */
 
 /**
diff --git a/include/sqfs/block_writer.h b/include/sqfs/block_writer.h
index bd1ddfc..674c0e7 100644
--- a/include/sqfs/block_writer.h
+++ b/include/sqfs/block_writer.h
@@ -34,6 +34,8 @@
  * @implements sqfs_object_t
  *
  * @brief Abstracts writing and deduplicating of data and fragment blocks.
+ *
+ * This object is not copyable, i.e. @ref sqfs_copy will always return NULL.
  */
 
 /**
diff --git a/include/sqfs/compressor.h b/include/sqfs/compressor.h
index 4292712..9a3508a 100644
--- a/include/sqfs/compressor.h
+++ b/include/sqfs/compressor.h
@@ -91,15 +91,6 @@ struct sqfs_compressor_t {
 	 */
 	sqfs_s32 (*do_block)(sqfs_compressor_t *cmp, const sqfs_u8 *in,
 			     sqfs_u32 size, sqfs_u8 *out, sqfs_u32 outsize);
-
-	/**
-	 * @brief Create an exact copt of agiven compressor
-	 *
-	 * @param cmp A pointer to a compressor object.
-	 *
-	 * @return A deep copy of the given compressor.
-	 */
-	sqfs_compressor_t *(*create_copy)(sqfs_compressor_t *cmp);
 };
 
 /**
diff --git a/include/sqfs/dir_writer.h b/include/sqfs/dir_writer.h
index e4a26c7..dce5a79 100644
--- a/include/sqfs/dir_writer.h
+++ b/include/sqfs/dir_writer.h
@@ -58,6 +58,8 @@
  * adding entries. Internally it fills data into a meta data writer and
  * generates an index that it can, on request, write to another meta data
  * writer used for inodes.
+ *
+ * This object is not copyable, i.e. @ref sqfs_copy will always return NULL.
  */
 
 /**
diff --git a/include/sqfs/io.h b/include/sqfs/io.h
index 578c4fb..18c6810 100644
--- a/include/sqfs/io.h
+++ b/include/sqfs/io.h
@@ -63,6 +63,11 @@ typedef enum {
  * @extends sqfs_object_t
  *
  * @brief Abstracts file I/O to make it easy to embedd SquashFS.
+ *
+ * Files are only copyable if they are read only, i.e. if a file has been
+ * opened with write access, @ref sqfs_copy will always return NULL. The
+ * other data types inside libsquashfs assume this to hold for all
+ * implementations of this interface.
  */
 struct sqfs_file_t {
 	sqfs_object_t base;
diff --git a/include/sqfs/meta_writer.h b/include/sqfs/meta_writer.h
index be151cc..58968f5 100644
--- a/include/sqfs/meta_writer.h
+++ b/include/sqfs/meta_writer.h
@@ -46,6 +46,8 @@
  * The main task of the meta data writer is to provide a simple append
  * function that transparently takes care of chopping data up into blocks,
  * compressing the blocks and pre-pending a header.
+ *
+ * This object is not copyable, i.e. @ref sqfs_copy will always return NULL.
  */
 
 /**
diff --git a/include/sqfs/predef.h b/include/sqfs/predef.h
index 6ca3503..0e81933 100644
--- a/include/sqfs/predef.h
+++ b/include/sqfs/predef.h
@@ -121,6 +121,8 @@ typedef struct sqfs_xattr_id_table_t sqfs_xattr_id_table_t;
  */
 typedef struct sqfs_object_t {
 	void (*destroy)(struct sqfs_object_t *instance);
+
+	struct sqfs_object_t *(*copy)(const struct sqfs_object_t *orig);
 } sqfs_object_t;
 
 /**
@@ -135,4 +137,22 @@ static SQFS_INLINE void sqfs_destroy(void *obj)
 	((sqfs_object_t *)obj)->destroy(obj);
 }
 
+/**
+ * @brief Create a deep copy of an object if possible.
+ *
+ * @memberof sqfs_object_t
+ *
+ * @param obj A pointer to an object
+ *
+ * @return A pointer to a new object, instantiated from the old on success,
+ *         NULL on failure.
+ */
+static SQFS_INLINE void *sqfs_copy(const void *obj)
+{
+	if (((sqfs_object_t *)obj)->copy != NULL)
+		return ((sqfs_object_t *)obj)->copy(obj);
+
+	return NULL;
+}
+
 #endif /* SQFS_PREDEF_H */