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

lib/full-write.c

@@ -0,0 +1,80 @@
+/* An interface to read and write that retries (if necessary) until complete.
+
+   Copyright (C) 1993, 1994, 1997, 1998, 1999, 2000, 2001, 2002, 2003,
+   2004, 2005, 2006 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 <config.h>
+
+/* Specification.  */
+#ifdef FULL_READ
+# include "full-read.h"
+#else
+# include "full-write.h"
+#endif
+
+#include <errno.h>
+
+#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
+
+/* Write(read) COUNT bytes at BUF to(from) descriptor FD, retrying if
+   interrupted or if a partial write(read) occurs.  Return the number
+   of bytes transferred.
+   When writing, set errno if fewer than COUNT bytes are written.
+   When reading, if fewer than COUNT bytes are read, you must examine
+   errno to distinguish failure from EOF (errno == 0).  */
+size_t
+full_rw (int fd, const void *buf, size_t count)
+{
+  size_t total = 0;
+  const char *ptr = (const char *) buf;
+
+  while (count > 0)
+    {
+      size_t n_rw = safe_rw (fd, ptr, count);
+      if (n_rw == (size_t) -1)
+	break;
+      if (n_rw == 0)
+	{
+	  errno = ZERO_BYTE_TRANSFER_ERRNO;
+	  break;
+	}
+      total += n_rw;
+      ptr += n_rw;
+      count -= n_rw;
+    }
+
+  return total;
+}