-int bf_close (BFile);
-BFile bf_open (const char *name, int block_size, int cache);
-BFile bf_open_w (const char *name, int block_size, int cache);
-int bf_read (BFile bf, int no, void *buf);
-int bf_write (BFile bf, int no, const void *buf);
+/* bf_read: reads bytes from bfile 'bf'.
+ reads 'nbytes' bytes (or whole block if 0) from offset 'offset' from
+ block 'no'. stores contents in buffer 'buf'.
+ returns 1 if whole block could be read; 0 otherwise.
+ */
+int bf_read (BFile bf, zint no, int offset, int nbytes, void *buf);
+
+/* bf_write: writes bytes to bfile 'bf'.
+ writes 'nbytes' bytes (or whole block if 0) at offset 'offset' to
+ block 'no'. retrieves contents from buffer 'buf'.
+ returns 0 if successful; non-zero otherwise.
+ */
+int bf_write (BFile bf, zint no, int offset, int nbytes, const void *buf);
+
+/* bf_cache: enables bfile cache if spec is not NULL */
+void bf_cache (BFiles bfs, const char *spec);
+
+/* bf_commitExists: returns 1 if commit is pending; 0 otherwise */
+int bf_commitExists (BFiles bfs);
+
+/* bf_commitExec: executes commit */
+void bf_commitExec (BFiles bfs);