text: move I/O related code to separate file

This groups all I/O related code together to make it reusable in different
core text data structure implementations.

Makefile

@@ -9,6 +9,7 @@ SRC = array.c \
 	map.c \
 	sam.c \
 	text.c \
+	text-io.c \
 	text-motions.c \
 	text-objects.c \
 	text-util.c \

text-internal.h

@@ -0,0 +1,35 @@
+#ifndef TEXT_INTERNAL
+#define TEXT_INTERNAL
+
+#include <stdbool.h>
+#include <stddef.h>
+#include "text.h"
+
+/* Block holding the file content, either readonly mmap(2)-ed from the original
+ * file or heap allocated to store the modifications.
+ */
+typedef struct {
+	size_t size;               /* maximal capacity */
+	size_t len;                /* current used length / insertion position */
+	char *data;                /* actual data */
+	enum {                     /* type of allocation */
+		BLOCK_TYPE_MMAP_ORIG, /* mmap(2)-ed from an external file */
+		BLOCK_TYPE_MMAP,      /* mmap(2)-ed from a temporary file only known to this process */
+		BLOCK_TYPE_MALLOC,    /* heap allocated block using malloc(3) */
+	} type;
+} Block;
+
+Block *block_alloc(size_t size);
+Block *block_read(size_t size, int fd);
+Block *block_mmap(size_t size, int fd, off_t offset);
+Block *block_load(int dirfd, const char *filename, enum TextLoadMethod method, struct stat *info);
+void block_free(Block*);
+bool block_capacity(Block*, size_t len);
+const char *block_append(Block*, const char *data, size_t len);
+bool block_insert(Block*, size_t pos, const char *data, size_t len);
+bool block_delete(Block*, size_t pos, size_t len);
+
+Block *text_block_mmaped(Text*);
+void text_saved(Text*, struct stat *meta);
+
+#endif