Add a generic copying mechanism to sqfs_object_t

This patch adds a deep-copy callback to sqfs_object_t and removes the
copying mechanism from sqfs_compressor_t. This is also interesting for
other types.

Signed-off-by: David Oberhollenzer <david.oberhollenzer@sigma-star.at>

23 files changed, 374 insertions, 28 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 */
diff --git a/lib/common/comp_lzo.c b/lib/common/comp_lzo.c
index 8d0335e..24f4009 100644
--- a/lib/common/comp_lzo.c
+++ b/lib/common/comp_lzo.c
@@ -199,7 +199,7 @@ static void lzo_get_configuration(const sqfs_compressor_t *base,
 		cfg->flags |= SQFS_COMP_FLAG_UNCOMPRESS;
 }
 
-static sqfs_compressor_t *lzo_create_copy(sqfs_compressor_t *cmp)
+static sqfs_object_t *lzo_create_copy(const sqfs_object_t *cmp)
 {
 	lzo_compressor_t *other = (lzo_compressor_t *)cmp;
 	lzo_compressor_t *lzo;
@@ -209,7 +209,7 @@ static sqfs_compressor_t *lzo_create_copy(sqfs_compressor_t *cmp)
 		return NULL;
 
 	memcpy(lzo, other, sizeof(*lzo));
-	return (sqfs_compressor_t *)lzo;
+	return (sqfs_object_t *)lzo;
 }
 
 static void lzo_destroy(sqfs_object_t *base)
@@ -270,7 +270,7 @@ sqfs_compressor_t *lzo_compressor_create(const sqfs_compressor_config_t *cfg)
 		lzo_uncomp_block : lzo_comp_block;
 	base->write_options = lzo_write_options;
 	base->read_options = lzo_read_options;
-	base->create_copy = lzo_create_copy;
+	((sqfs_object_t *)base)->copy = lzo_create_copy;
 	((sqfs_object_t *)base)->destroy = lzo_destroy;
 	return base;
 }
diff --git a/lib/sqfs/block_processor/winpthread.c b/lib/sqfs/block_processor/winpthread.c
index 47f4e35..1aa77e7 100644
--- a/lib/sqfs/block_processor/winpthread.c
+++ b/lib/sqfs/block_processor/winpthread.c
@@ -232,7 +232,7 @@ static thread_pool_processor_t *block_processor_create(size_t max_block_size,
 			goto fail;
 
 		proc->workers[i]->shared = proc;
-		proc->workers[i]->cmp = cmp->create_copy(cmp);
+		proc->workers[i]->cmp = sqfs_copy(cmp);
 
 		if (proc->workers[i]->cmp == NULL)
 			goto fail;
diff --git a/lib/sqfs/comp/gzip.c b/lib/sqfs/comp/gzip.c
index 34164a6..351d733 100644
--- a/lib/sqfs/comp/gzip.c
+++ b/lib/sqfs/comp/gzip.c
@@ -221,7 +221,7 @@ static sqfs_s32 gzip_do_block(sqfs_compressor_t *base, const sqfs_u8 *in,
 	return 0;
 }
 
-static sqfs_compressor_t *gzip_create_copy(sqfs_compressor_t *cmp)
+static sqfs_object_t *gzip_create_copy(const sqfs_object_t *cmp)
 {
 	gzip_compressor_t *gzip = malloc(sizeof(*gzip));
 	int ret;
@@ -244,7 +244,7 @@ static sqfs_compressor_t *gzip_create_copy(sqfs_compressor_t *cmp)
 		return NULL;
 	}
 
-	return (sqfs_compressor_t *)gzip;
+	return (sqfs_object_t *)gzip;
 }
 
 sqfs_compressor_t *gzip_compressor_create(const sqfs_compressor_config_t *cfg)
@@ -283,7 +283,7 @@ sqfs_compressor_t *gzip_compressor_create(const sqfs_compressor_config_t *cfg)
 	base->do_block = gzip_do_block;
 	base->write_options = gzip_write_options;
 	base->read_options = gzip_read_options;
-	base->create_copy = gzip_create_copy;
+	((sqfs_object_t *)base)->copy = gzip_create_copy;
 	((sqfs_object_t *)base)->destroy = gzip_destroy;
 
 	if (gzip->compress) {
diff --git a/lib/sqfs/comp/lz4.c b/lib/sqfs/comp/lz4.c
index f298c67..460ac44 100644
--- a/lib/sqfs/comp/lz4.c
+++ b/lib/sqfs/comp/lz4.c
@@ -116,7 +116,7 @@ static void lz4_get_configuration(const sqfs_compressor_t *base,
 		cfg->flags |= SQFS_COMP_FLAG_UNCOMPRESS;
 }
 
-static sqfs_compressor_t *lz4_create_copy(sqfs_compressor_t *cmp)
+static sqfs_object_t *lz4_create_copy(const sqfs_object_t *cmp)
 {
 	lz4_compressor_t *lz4 = malloc(sizeof(*lz4));
 
@@ -124,7 +124,7 @@ static sqfs_compressor_t *lz4_create_copy(sqfs_compressor_t *cmp)
 		return NULL;
 
 	memcpy(lz4, cmp, sizeof(*lz4));
-	return (sqfs_compressor_t *)lz4;
+	return (sqfs_object_t *)lz4;
 }
 
 static void lz4_destroy(sqfs_object_t *base)
@@ -155,7 +155,7 @@ sqfs_compressor_t *lz4_compressor_create(const sqfs_compressor_config_t *cfg)
 		lz4_uncomp_block : lz4_comp_block;
 	base->write_options = lz4_write_options;
 	base->read_options = lz4_read_options;
-	base->create_copy = lz4_create_copy;
+	((sqfs_object_t *)base)->copy = lz4_create_copy;
 	((sqfs_object_t *)base)->destroy = lz4_destroy;
 	return base;
 }
diff --git a/lib/sqfs/comp/lzma.c b/lib/sqfs/comp/lzma.c
index 451a6ca..51afe65 100644
--- a/lib/sqfs/comp/lzma.c
+++ b/lib/sqfs/comp/lzma.c
@@ -156,14 +156,14 @@ static void lzma_get_configuration(const sqfs_compressor_t *base,
 		cfg->flags |= SQFS_COMP_FLAG_UNCOMPRESS;
 }
 
-static sqfs_compressor_t *lzma_create_copy(sqfs_compressor_t *cmp)
+static sqfs_object_t *lzma_create_copy(const sqfs_object_t *cmp)
 {
 	lzma_compressor_t *copy = malloc(sizeof(*copy));
 
 	if (copy != NULL)
 		memcpy(copy, cmp, sizeof(*copy));
 
-	return (sqfs_compressor_t *)copy;
+	return (sqfs_object_t *)copy;
 }
 
 static void lzma_destroy(sqfs_object_t *base)
@@ -194,7 +194,7 @@ sqfs_compressor_t *lzma_compressor_create(const sqfs_compressor_config_t *cfg)
 		lzma_uncomp_block : lzma_comp_block;
 	base->write_options = lzma_write_options;
 	base->read_options = lzma_read_options;
-	base->create_copy = lzma_create_copy;
+	((sqfs_object_t *)base)->copy = lzma_create_copy;
 	((sqfs_object_t *)base)->destroy = lzma_destroy;
 	return base;
 }
diff --git a/lib/sqfs/comp/xz.c b/lib/sqfs/comp/xz.c
index a600956..423604b 100644
--- a/lib/sqfs/comp/xz.c
+++ b/lib/sqfs/comp/xz.c
@@ -211,7 +211,7 @@ static void xz_get_configuration(const sqfs_compressor_t *base,
 		cfg->flags |= SQFS_COMP_FLAG_UNCOMPRESS;
 }
 
-static sqfs_compressor_t *xz_create_copy(sqfs_compressor_t *cmp)
+static sqfs_object_t *xz_create_copy(const sqfs_object_t *cmp)
 {
 	xz_compressor_t *xz = malloc(sizeof(*xz));
 
@@ -219,7 +219,7 @@ static sqfs_compressor_t *xz_create_copy(sqfs_compressor_t *cmp)
 		return NULL;
 
 	memcpy(xz, cmp, sizeof(*xz));
-	return (sqfs_compressor_t *)xz;
+	return (sqfs_object_t *)xz;
 }
 
 static void xz_destroy(sqfs_object_t *base)
@@ -253,7 +253,7 @@ sqfs_compressor_t *xz_compressor_create(const sqfs_compressor_config_t *cfg)
 		xz_uncomp_block : xz_comp_block;
 	base->write_options = xz_write_options;
 	base->read_options = xz_read_options;
-	base->create_copy = xz_create_copy;
+	((sqfs_object_t *)base)->copy = xz_create_copy;
 	((sqfs_object_t *)base)->destroy = xz_destroy;
 	return base;
 }
diff --git a/lib/sqfs/comp/zstd.c b/lib/sqfs/comp/zstd.c
index e01f87d..12ddfdb 100644
--- a/lib/sqfs/comp/zstd.c
+++ b/lib/sqfs/comp/zstd.c
@@ -107,7 +107,7 @@ static void zstd_get_configuration(const sqfs_compressor_t *base,
 		cfg->flags |= SQFS_COMP_FLAG_UNCOMPRESS;
 }
 
-static sqfs_compressor_t *zstd_create_copy(sqfs_compressor_t *cmp)
+static sqfs_object_t *zstd_create_copy(const sqfs_object_t *cmp)
 {
 	zstd_compressor_t *zstd = malloc(sizeof(*zstd));
 
@@ -123,7 +123,7 @@ static sqfs_compressor_t *zstd_create_copy(sqfs_compressor_t *cmp)
 		return NULL;
 	}
 
-	return (sqfs_compressor_t *)zstd;
+	return (sqfs_object_t *)zstd;
 }
 
 static void zstd_destroy(sqfs_object_t *base)
@@ -164,7 +164,7 @@ sqfs_compressor_t *zstd_compressor_create(const sqfs_compressor_config_t *cfg)
 		zstd_uncomp_block : zstd_comp_block;
 	base->write_options = zstd_write_options;
 	base->read_options = zstd_read_options;
-	base->create_copy = zstd_create_copy;
+	((sqfs_object_t *)base)->copy = zstd_create_copy;
 	((sqfs_object_t *)base)->destroy = zstd_destroy;
 	return base;
 }
diff --git a/lib/sqfs/data_reader.c b/lib/sqfs/data_reader.c
index 5e985e0..cd9ad68 100644
--- a/lib/sqfs/data_reader.c
+++ b/lib/sqfs/data_reader.c
@@ -137,6 +137,51 @@ static void data_reader_destroy(sqfs_object_t *obj)
 	free(data);
 }
 
+static sqfs_object_t *data_reader_copy(const sqfs_object_t *obj)
+{
+	const sqfs_data_reader_t *data = (const sqfs_data_reader_t *)obj;
+	sqfs_data_reader_t *copy;
+
+	copy = alloc_flex(sizeof(*data), 1, data->block_size);
+	if (copy == NULL)
+		return NULL;
+
+	memcpy(copy, data, sizeof(*data) + data->block_size);
+
+	copy->frag_tbl = sqfs_copy(data->frag_tbl);
+	if (copy->frag_tbl == NULL)
+		goto fail_ftbl;
+
+	if (data->data_block != NULL) {
+		copy->data_block = malloc(data->data_blk_size);
+		if (copy->data_block == NULL)
+			goto fail_dblk;
+
+		memcpy(copy->data_block, data->data_block,
+		       data->data_blk_size);
+	}
+
+	if (copy->frag_block != NULL) {
+		copy->frag_block = malloc(copy->frag_blk_size);
+		if (copy->frag_block == NULL)
+			goto fail_fblk;
+
+		memcpy(copy->frag_block, data->frag_block,
+		       data->frag_blk_size);
+	}
+
+	/* XXX: file and cmp aren't deep-copied becaues data
+	        doesn't own them either. */
+	return (sqfs_object_t *)copy;
+fail_fblk:
+	free(copy->data_block);
+fail_dblk:
+	sqfs_destroy(copy->frag_tbl);
+fail_ftbl:
+	free(copy);
+	return NULL;
+}
+
 sqfs_data_reader_t *sqfs_data_reader_create(sqfs_file_t *file,
 					    size_t block_size,
 					    sqfs_compressor_t *cmp)
@@ -153,6 +198,7 @@ sqfs_data_reader_t *sqfs_data_reader_create(sqfs_file_t *file,
 	}
 
 	((sqfs_object_t *)data)->destroy = data_reader_destroy;
+	((sqfs_object_t *)data)->copy = data_reader_copy;
 	data->file = file;
 	data->block_size = block_size;
 	data->cmp = cmp;
diff --git a/lib/sqfs/dir_reader.c b/lib/sqfs/dir_reader.c
index 4e2a5b8..8e23ddb 100644
--- a/lib/sqfs/dir_reader.c
+++ b/lib/sqfs/dir_reader.c
@@ -45,6 +45,32 @@ static void dir_reader_destroy(sqfs_object_t *obj)
 	free(rd);
 }
 
+static sqfs_object_t *dir_reader_copy(const sqfs_object_t *obj)
+{
+	const sqfs_dir_reader_t *rd = (const sqfs_dir_reader_t *)obj;
+	sqfs_dir_reader_t *copy  = malloc(sizeof(*copy));
+
+	if (copy == NULL)
+		return NULL;
+
+	memcpy(copy, rd, sizeof(*copy));
+
+	copy->meta_inode = sqfs_copy(rd->meta_inode);
+	if (copy->meta_inode == NULL)
+		goto fail_mino;
+
+	copy->meta_dir = sqfs_copy(rd->meta_dir);
+	if (copy->meta_dir == NULL)
+		goto fail_mdir;
+
+	return (sqfs_object_t *)copy;
+fail_mdir:
+	sqfs_destroy(copy->meta_inode);
+fail_mino:
+	free(copy);
+	return NULL;
+}
+
 sqfs_dir_reader_t *sqfs_dir_reader_create(const sqfs_super_t *super,
 					  sqfs_compressor_t *cmp,
 					  sqfs_file_t *file)
@@ -83,6 +109,7 @@ sqfs_dir_reader_t *sqfs_dir_reader_create(const sqfs_super_t *super,
 	}
 
 	((sqfs_object_t *)rd)->destroy = dir_reader_destroy;
+	((sqfs_object_t *)rd)->copy = dir_reader_copy;
 	rd->super = super;
 	return rd;
 }
diff --git a/lib/sqfs/frag_table.c b/lib/sqfs/frag_table.c
index bf1c109..51164e6 100644
--- a/lib/sqfs/frag_table.c
+++ b/lib/sqfs/frag_table.c
@@ -58,6 +58,44 @@ static void frag_table_destroy(sqfs_object_t *obj)
 	free(tbl);
 }
 
+static sqfs_object_t *frag_table_copy(const sqfs_object_t *obj)
+{
+	const sqfs_frag_table_t *tbl = (const sqfs_frag_table_t *)obj;
+	sqfs_frag_table_t *copy;
+	const chunk_info_t *it;
+	chunk_info_t *last;
+	size_t i;
+
+	copy = malloc(sizeof(*copy));
+	if (copy == NULL)
+		return NULL;
+
+	memcpy(copy, tbl, sizeof(*tbl));
+	for (i = 0; i < NUM_BUCKETS; ++i)
+		copy->chunks[i].next = NULL;
+
+	for (i = 0; i < NUM_BUCKETS; ++i) {
+		last = &(copy->chunks[i]);
+		it = tbl->chunks[i].next;
+
+		while (it != NULL) {
+			last->next = malloc(sizeof(*it));
+			if (last->next == NULL)
+				goto fail;
+
+			memcpy(last->next, it, sizeof(*it));
+			last = last->next;
+			last->next = NULL;
+			it = it->next;
+		}
+	}
+
+	return (sqfs_object_t *)copy;
+fail:
+	frag_table_destroy((sqfs_object_t *)copy);
+	return NULL;
+}
+
 sqfs_frag_table_t *sqfs_frag_table_create(sqfs_u32 flags)
 {
 	sqfs_frag_table_t *tbl;
@@ -69,6 +107,7 @@ sqfs_frag_table_t *sqfs_frag_table_create(sqfs_u32 flags)
 	if (tbl == NULL)
 		return NULL;
 
+	((sqfs_object_t *)tbl)->copy = frag_table_copy;
 	((sqfs_object_t *)tbl)->destroy = frag_table_destroy;
 	return tbl;
 }
diff --git a/lib/sqfs/id_table.c b/lib/sqfs/id_table.c
index 86f2809..e3d386e 100644
--- a/lib/sqfs/id_table.c
+++ b/lib/sqfs/id_table.c
@@ -32,6 +32,30 @@ static void id_table_destroy(sqfs_object_t *obj)
 	free(tbl);
 }
 
+static sqfs_object_t *id_table_copy(const sqfs_object_t *obj)
+{
+	const sqfs_id_table_t *tbl = (const sqfs_id_table_t *)obj;
+	sqfs_id_table_t *copy;
+
+	copy = malloc(sizeof(*copy));
+	if (copy == NULL)
+		return NULL;
+
+	memcpy(copy, tbl, sizeof(*tbl));
+
+	copy->num_ids = tbl->num_ids;
+	copy->max_ids = tbl->num_ids;
+	copy->ids = malloc(tbl->num_ids * sizeof(tbl->ids[0]));
+
+	if (copy->ids == NULL) {
+		free(copy);
+		return NULL;
+	}
+
+	memcpy(copy->ids, tbl->ids, tbl->num_ids * sizeof(tbl->ids[0]));
+	return (sqfs_object_t *)copy;
+}
+
 sqfs_id_table_t *sqfs_id_table_create(sqfs_u32 flags)
 {
 	sqfs_id_table_t *tbl;
@@ -43,6 +67,7 @@ sqfs_id_table_t *sqfs_id_table_create(sqfs_u32 flags)
 
 	if (tbl != NULL) {
 		((sqfs_object_t *)tbl)->destroy = id_table_destroy;
+		((sqfs_object_t *)tbl)->copy = id_table_copy;
 	}
 
 	return tbl;
diff --git a/lib/sqfs/meta_reader.c b/lib/sqfs/meta_reader.c
index 8fd7f21..b16b115 100644
--- a/lib/sqfs/meta_reader.c
+++ b/lib/sqfs/meta_reader.c
@@ -51,6 +51,20 @@ static void meta_reader_destroy(sqfs_object_t *m)
 	free(m);
 }
 
+static sqfs_object_t *meta_reader_copy(const sqfs_object_t *obj)
+{
+	const sqfs_meta_reader_t *m = (const sqfs_meta_reader_t *)obj;
+	sqfs_meta_reader_t *copy = malloc(sizeof(*copy));
+
+	if (copy != NULL) {
+		memcpy(copy, m, sizeof(*m));
+	}
+
+	/* XXX: cmp and file aren't deep-copied because m
+	        doesn't own them either. */
+	return (sqfs_object_t *)copy;
+}
+
 sqfs_meta_reader_t *sqfs_meta_reader_create(sqfs_file_t *file,
 					    sqfs_compressor_t *cmp,
 					    sqfs_u64 start, sqfs_u64 limit)
@@ -60,6 +74,7 @@ sqfs_meta_reader_t *sqfs_meta_reader_create(sqfs_file_t *file,
 	if (m == NULL)
 		return NULL;
 
+	((sqfs_object_t *)m)->copy = meta_reader_copy;
 	((sqfs_object_t *)m)->destroy = meta_reader_destroy;
 	m->start = start;
 	m->limit = limit;
diff --git a/lib/sqfs/unix/io_file.c b/lib/sqfs/unix/io_file.c
index 1c181ab..52fc94b 100644
--- a/lib/sqfs/unix/io_file.c
+++ b/lib/sqfs/unix/io_file.c
@@ -13,6 +13,7 @@
 #include <sys/stat.h>
 #include <stdlib.h>
 #include <unistd.h>
+#include <string.h>
 #include <errno.h>
 #include <fcntl.h>
 
@@ -20,6 +21,7 @@
 typedef struct {
 	sqfs_file_t base;
 
+	bool readonly;
 	sqfs_u64 size;
 	int fd;
 } sqfs_file_stdio_t;
@@ -33,6 +35,34 @@ static void stdio_destroy(sqfs_object_t *base)
 	free(file);
 }
 
+static sqfs_object_t *stdio_copy(const sqfs_object_t *base)
+{
+	const sqfs_file_stdio_t *file = (const sqfs_file_stdio_t *)base;
+	sqfs_file_stdio_t *copy;
+	int err;
+
+	if (!file->readonly) {
+		errno = ENOTSUP;
+		return NULL;
+	}
+
+	copy = calloc(1, sizeof(*copy));
+	if (copy == NULL)
+		return NULL;
+
+	memcpy(copy, file, sizeof(*file));
+
+	copy->fd = dup(file->fd);
+	if (copy->fd < 0) {
+		err = errno;
+		free(copy);
+		copy = NULL;
+		errno = err;
+	}
+
+	return (sqfs_object_t *)copy;
+}
+
 static int stdio_read_at(sqfs_file_t *base, sqfs_u64 offset,
 			 void *buffer, size_t size)
 {
@@ -125,8 +155,10 @@ sqfs_file_t *sqfs_open_file(const char *filename, sqfs_u32 flags)
 		return NULL;
 
 	if (flags & SQFS_FILE_OPEN_READ_ONLY) {
+		file->readonly = true;
 		open_mode = O_RDONLY;
 	} else {
+		file->readonly = false;
 		open_mode = O_CREAT | O_RDWR;
 
 		if (flags & SQFS_FILE_OPEN_OVERWRITE) {
@@ -158,6 +190,7 @@ sqfs_file_t *sqfs_open_file(const char *filename, sqfs_u32 flags)
 	base->write_at = stdio_write_at;
 	base->get_size = stdio_get_size;
 	base->truncate = stdio_truncate;
+	((sqfs_object_t *)base)->copy = stdio_copy;
 	((sqfs_object_t *)base)->destroy = stdio_destroy;
 	return base;
 }
diff --git a/lib/sqfs/win32/io_file.c b/lib/sqfs/win32/io_file.c
index c1849a8..836aa37 100644
--- a/lib/sqfs/win32/io_file.c
+++ b/lib/sqfs/win32/io_file.c
@@ -19,6 +19,7 @@
 typedef struct {
 	sqfs_file_t base;
 
+	bool readonly;
 	sqfs_u64 size;
 	HANDLE fd;
 } sqfs_file_stdio_t;
@@ -32,6 +33,35 @@ static void stdio_destroy(sqfs_object_t *base)
 	free(file);
 }
 
+static sqfs_object_t *stdio_copy(const sqfs_object_t *base)
+{
+	const sqfs_file_stdio_t *file = (const sqfs_file_stdio_t *)base;
+	sqfs_file_stdio_t *copy;
+	BOOL ret;
+
+	if (!file->readonly) {
+		SetLastError(ERROR_NOT_SUPPORTED);
+		return NULL;
+	}
+
+	copy = calloc(1, sizeof(*copy));
+	if (copy == NULL)
+		return NULL;
+
+	memcpy(copy, file, sizeof(*file));
+
+	ret = DuplicateHandle(GetCurrentProcess(), file->fd,
+			      GetCurrentProcess(), &copy->fd,
+			      0, FALSE, DUPLICATE_SAME_ACCESS);
+
+	if (!ret) {
+		free(copy);
+		return NULL;
+	}
+
+	return (sqfs_object_t *)copy;
+}
+
 static int stdio_read_at(sqfs_file_t *base, sqfs_u64 offset,
 			 void *buffer, size_t size)
 {
@@ -135,9 +165,11 @@ sqfs_file_t *sqfs_open_file(const char *filename, sqfs_u32 flags)
 		return NULL;
 
 	if (flags & SQFS_FILE_OPEN_READ_ONLY) {
+		file->readonly = true;
 		access_flags = GENERIC_READ;
 		creation_mode = OPEN_EXISTING;
 	} else {
+		file->readonly = false;
 		access_flags = GENERIC_READ | GENERIC_WRITE;
 
 		if (flags & SQFS_FILE_OPEN_OVERWRITE) {
@@ -166,5 +198,6 @@ sqfs_file_t *sqfs_open_file(const char *filename, sqfs_u32 flags)
 	base->get_size = stdio_get_size;
 	base->truncate = stdio_truncate;
 	((sqfs_object_t *)base)->destroy = stdio_destroy;
+	((sqfs_object_t *)base)->copy = stdio_copy;
 	return base;
 }
diff --git a/lib/sqfs/xattr_reader.c b/lib/sqfs/xattr_reader.c
index 97cf821..1469a90 100644
--- a/lib/sqfs/xattr_reader.c
+++ b/lib/sqfs/xattr_reader.c
@@ -36,6 +36,50 @@ struct sqfs_xattr_reader_t {
 	sqfs_file_t *file;
 };
 
+static sqfs_object_t *xattr_reader_copy(const sqfs_object_t *obj)
+{
+	const sqfs_xattr_reader_t *xr = (const sqfs_xattr_reader_t *)obj;
+	sqfs_xattr_reader_t *copy = malloc(sizeof(*copy));
+
+	if (copy == NULL)
+		return NULL;
+
+	memcpy(copy, xr, sizeof(*xr));
+
+	if (xr->kvrd != NULL) {
+		copy->kvrd = sqfs_copy(xr->kvrd);
+		if (copy->kvrd == NULL)
+			goto fail_kvrd;
+	}
+
+	if (xr->idrd != NULL) {
+		copy->idrd = sqfs_copy(xr->idrd);
+		if (copy->idrd == NULL)
+			goto fail_idrd;
+	}
+
+	if (xr->id_block_starts != NULL) {
+		copy->id_block_starts = alloc_array(sizeof(sqfs_u64),
+						    xr->num_id_blocks);
+		if (copy->id_block_starts == NULL)
+			goto fail_idblk;
+
+		memcpy(copy->id_block_starts, xr->id_block_starts,
+		       sizeof(sqfs_u64) * xr->num_id_blocks);
+	}
+
+	return (sqfs_object_t *)copy;
+fail_idblk:
+	if (copy->idrd != NULL)
+		sqfs_destroy(copy->idrd);
+fail_idrd:
+	if (copy->kvrd != NULL)
+		sqfs_destroy(copy->kvrd);
+fail_kvrd:
+	free(copy);
+	return NULL;
+}
+
 static void xattr_reader_destroy(sqfs_object_t *obj)
 {
 	sqfs_xattr_reader_t *xr = (sqfs_xattr_reader_t *)obj;
@@ -267,6 +311,7 @@ sqfs_xattr_reader_t *sqfs_xattr_reader_create(sqfs_file_t *file,
 	if (xr == NULL)
 		return NULL;
 
+	((sqfs_object_t *)xr)->copy = xattr_reader_copy;
 	((sqfs_object_t *)xr)->destroy = xattr_reader_destroy;
 	xr->file = file;
 	xr->super = super;
diff --git a/lib/sqfs/xattr_writer.c b/lib/sqfs/xattr_writer.c
index 827d0c5..488fd43 100644
--- a/lib/sqfs/xattr_writer.c
+++ b/lib/sqfs/xattr_writer.c
@@ -115,6 +115,64 @@ struct sqfs_xattr_writer_t {
 };
 
 
+static sqfs_object_t *xattr_writer_copy(const sqfs_object_t *obj)
+{
+	const sqfs_xattr_writer_t *xwr = (const sqfs_xattr_writer_t *)obj;
+	kv_block_desc_t *blk, *it, **next;
+	sqfs_xattr_writer_t *copy;
+
+	copy = calloc(1, sizeof(*copy));
+	if (copy == NULL)
+		return NULL;
+
+	memcpy(copy, xwr, sizeof(*xwr));
+
+	if (str_table_copy(&copy->keys, &xwr->keys))
+		goto fail_keys;
+
+	if (str_table_copy(&copy->values, &xwr->values))
+		goto fail_values;
+
+	copy->max_pairs = xwr->num_pairs;
+	copy->num_pairs = xwr->num_pairs;
+
+	copy->kv_pairs = malloc(sizeof(copy->kv_pairs[0]) * xwr->num_pairs);
+	if (copy->kv_pairs == NULL)
+		goto fail_pairs;
+
+	memcpy(copy->kv_pairs, xwr->kv_pairs,
+	       sizeof(copy->kv_pairs[0]) * xwr->num_pairs);
+
+	next = &(copy->kv_blocks);
+
+	for (it = xwr->kv_blocks; it != NULL; it = it->next) {
+		blk = malloc(sizeof(*blk));
+		if (blk == NULL)
+			goto fail_blk;
+
+		memcpy(blk, it, sizeof(*it));
+		blk->next = NULL;
+
+		*next = blk;
+		next = &(blk->next);
+	}
+
+	return (sqfs_object_t *)copy;
+fail_blk:
+	while (copy->kv_blocks != NULL) {
+		blk = copy->kv_blocks;
+		copy->kv_blocks = copy->kv_blocks->next;
+		free(blk);
+	}
+fail_pairs:
+	str_table_cleanup(&copy->values);
+fail_values:
+	str_table_cleanup(&copy->keys);
+fail_keys:
+	free(copy);
+	return NULL;
+}
+
 static void xattr_writer_destroy(sqfs_object_t *obj)
 {
 	sqfs_xattr_writer_t *xwr = (sqfs_xattr_writer_t *)obj;
@@ -148,6 +206,7 @@ sqfs_xattr_writer_t *sqfs_xattr_writer_create(void)
 	if (xwr->kv_pairs == NULL)
 		goto fail_pairs;
 
+	((sqfs_object_t *)xwr)->copy = xattr_writer_copy;
 	((sqfs_object_t *)xwr)->destroy = xattr_writer_destroy;
 	return xwr;
 fail_pairs: