Add support for repacking condensed sparse files

This commit broadly does the following things:
 - Rename and move the sparse mapping structure to libutil
 - Add a function to the data writer for writing condensed versions
   of sparse files, given the mapping.
 - This shares code with the already existing function for regular
   files. The shared code is moved to a common helper function.
 - Add support to tar2sqfs for repacking sparse files.

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

3 files changed, 24 insertions, 7 deletions

diff --git a/include/data_writer.h b/include/data_writer.h
index cafe61e..2ace899 100644
--- a/include/data_writer.h
+++ b/include/data_writer.h
@@ -5,6 +5,7 @@
 #include "squashfs.h"
 #include "compress.h"
 #include "fstree.h"
+#include "util.h"
 
 typedef struct data_writer_t data_writer_t;
 
@@ -42,8 +43,21 @@ int data_writer_flush_fragments(data_writer_t *data);
   The file_info_t object is updated accordingly and used to determine the
   number of bytes to write and the input file name to report errors.
 
+  Blocks or fragments that are all zero bytes automatically detected,
+  not written out and the sparse file accounting updated accordingly.
+
   Returns 0 on success, prints errors to stderr.
 */
 int write_data_from_fd(data_writer_t *data, file_info_t *fi, int infd);
 
+/*
+  Does the same as write_data_from_fd but the input file is the condensed
+  representation of a sparse file. The layout must be in order and
+  non-overlapping.
+
+  Returns 0 on success, prints errors to stderr.
+ */
+int write_data_from_fd_condensed(data_writer_t *data, file_info_t *fi,
+				 int infd, sparse_map_t *map);
+
 #endif /* DATA_WRITER_H */
diff --git a/include/tar.h b/include/tar.h
index 2819740..1f8ca7e 100644
--- a/include/tar.h
+++ b/include/tar.h
@@ -6,6 +6,8 @@
 #include <stdbool.h>
 #include <stdint.h>
 
+#include "util.h"
+
 typedef enum {
 	ETV_UNKNOWN = 0,
 	ETV_V7_UNIX,
@@ -61,17 +63,11 @@ typedef struct {
 	char padding[7];
 } gnu_sparse_t;
 
-typedef struct tar_sparse_data_t {
-	struct tar_sparse_data_t *next;
-	uint64_t offset;
-	uint64_t count;
-} tar_sparse_data_t;
-
 typedef struct {
 	struct stat sb;
 	char *name;
 	char *link_target;
-	tar_sparse_data_t *sparse;
+	sparse_map_t *sparse;
 	uint64_t sparse_size;
 	bool unknown_record;
 } tar_header_decoded_t;
diff --git a/include/util.h b/include/util.h
index d5b20dd..997cbf5 100644
--- a/include/util.h
+++ b/include/util.h
@@ -5,6 +5,13 @@
 #include <sys/types.h>
 #include <stdint.h>
 
+/* layout structure for sparse files, indicating where the actual data is */
+typedef struct sparse_map_t {
+	struct sparse_map_t *next;
+	uint64_t offset;
+	uint64_t count;
+} sparse_map_t;
+
 /*
   Convert back to forward slashed, remove all preceeding and trailing slashes,
   collapse all sequences of slashes, remove all path components that are '.'