-/* Write LEN bytes at PTR to descriptor DESC, retrying if interrupted.
- Return LEN upon success, write's (negative) error code otherwise. */
+#ifdef FULL_READ
+# include "safe-read.h"
+# define safe_rw safe_read
+# define full_rw full_read
+# undef const
+# define const /* empty */
+#else
+# include "safe-write.h"
+# define safe_rw safe_write
+# define full_rw full_write
+#endif
+
+#ifdef FULL_READ
+/* Set errno to zero upon EOF. */
+# define ZERO_BYTE_TRANSFER_ERRNO 0
+#else
+/* Some buggy drivers return 0 when one tries to write beyond
+ a device's end. (Example: Linux 1.2.13 on /dev/fd0.)
+ Set errno to ENOSPC so they get a sensible diagnostic. */
+# define ZERO_BYTE_TRANSFER_ERRNO ENOSPC
+#endif