Use Gnulib's full-write' and full-read' modules.

lib/safe-write.h

@@ -0,0 +1,24 @@
+/* An interface to write() that retries after interrupts.
+   Copyright (C) 2002 Free Software Foundation, Inc.
+
+   This program is free software: you can redistribute it and/or modify
+   it under the terms of the GNU Lesser General Public License as published by
+   the Free Software Foundation; either version 3 of the License, or
+   (at your option) any later version.
+
+   This program is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+   GNU Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public License
+   along with this program.  If not, see <http://www.gnu.org/licenses/>.  */
+
+#include <stddef.h>
+
+#define SAFE_WRITE_ERROR ((size_t) -1)
+
+/* Write up to COUNT bytes at BUF to descriptor FD, retrying if interrupted.
+   Return the actual number of bytes written, zero for EOF, or SAFE_WRITE_ERROR
+   upon error.  */
+extern size_t safe_write (int fd, const void *buf, size_t count);