cbfstool: Add buffer management API.

Many functions in cbfstool need to deal with a memory buffer - both location and
size. Right now it's made by different ways: for ROM image using global variable
(romsize, master_header); and in cbfs-* using return value for size and char**
to return memory location.

This may cause bugs like assuming incorrect return types, ex:
	uint32_t file_size = parse();	// which returns "-1" on error
	if (file_size <= 0) { ...
And the parse error will never be caught.

We can simplify this by introducing a buffer API, to change
	unsigned int do_something(char *input, size_t len, char **output, ...)
into
	int do_something(struct buffer *input, struct buffer *output, ...)

The buffer API will be used by further commits.

Change-Id: Iaddaeb109f08be6be84c6728d72c6a043b0e7a9f
Signed-off-by: Hung-Te Lin <hungte@chromium.org>
Reviewed-on: http://review.coreboot.org/2205
Tested-by: build bot (Jenkins)
Reviewed-by: Stefan Reinauer <stefan.reinauer@coreboot.org>

util/cbfstool/common.h

@@ -21,6 +21,7 @@
 #define __CBFSTOOL_COMMON_H
 
 #include <stdint.h>
+#include <assert.h>
 
 /* Endianess */
 #include "swab.h"
@@ -40,6 +41,27 @@ extern int verbose;
 #define INFO(x...) { if (verbose > 0) fprintf(stderr, "INFO: " x); }
 #define DEBUG(x...) { if (verbose > 1) fprintf(stderr, "DEBUG: " x); }
 
+/* Buffer and file I/O */
+struct buffer {
+	char *name;
+	char *data;
+	size_t size;
+};
+
+/* Creates an empty memory buffer with given size.
+ * Returns 0 on success, otherwise non-zero. */
+int buffer_create(struct buffer *buffer, size_t size, const char *name);
+
+/* Loads a file into memory buffer. Returns 0 on success, otherwise non-zero. */
+int buffer_from_file(struct buffer *buffer, const char *filename);
+
+/* Writes memory buffer content into file.
+ * Returns 0 on success, otherwise non-zero. */
+int buffer_write_file(struct buffer *buffer, const char *filename);
+
+/* Destroys a memory buffer. */
+void buffer_delete(struct buffer *buffer);
+
 extern void *offset;
 extern uint32_t romsize;
 extern int host_bigendian;