Add nbio interface. I'll fill it in soon.

nbio/nbio.h

@@ -0,0 +1,50 @@
+#include <stddef.h> /* size_t */
+#include <stdbool.h> /* bool */
+
+enum nbio_mode_t {
+	/* The comments tell which mode in fopen() it corresponds to. */
+	nbio_read,   /* rb */
+	nbio_write,  /* wb */
+	nbio_update, /* r+b */
+};
+struct nbio_t;
+
+/*
+ * Creates an nbio structure for performing the given operation on the given file.
+ */
+struct nbio_t* nbio_open(const char * filename, enum nbio_mode_t mode);
+
+/*
+ * Starts reading the given file. When done, it will be available in nbio_get_ptr.
+ * Can not be done if the structure was created with nbio_write.
+ */
+void nbio_begin_read(struct nbio_t* handle);
+
+/*
+ * Starts writing to the given file. Before this, you should've copied the data to nbio_get_ptr.
+ * Can not be done if the structure was created with nbio_read.
+ */
+void nbio_begin_write(struct nbio_t* handle);
+
+/*
+ * Performs part of the requested operation, or checks how it's going.
+ * When it returns true, it's done.
+ */
+bool nbio_iterate(struct nbio_t* handle, size_t* progress, size_t* len);
+
+/*
+ * Resizes the file to the given size.
+ * Can not be done if the structure was created with nbio_read.
+ */
+void nbio_resize(struct nbio_t* handle, size_t len);
+
+/*
+ * Returns a pointer to the file data. Writable only if structure was not created with nbio_read.
+ * Can not be done while any operation is in progress.
+ */
+void* nbio_get_ptr(struct nbio_t* handle, size_t* len);
+
+/*
+ * Deletes the nbio structure and its associated pointer.
+ */
+void nbio_free(struct nbio_t* handle);