Handle missing O_TMPFILE gracefully and document tempfile() in README

Signed-off-by: Joachim Nilsson <troglobit@gmail.com>

Makefile

@@ -39,7 +39,7 @@ STRIPINST  := $(INSTALL) -s --strip-program=$(CROSS)strip -m 0755
 CFLAGS     += -fPIC
 CFLAGS     += -Os
 CPPFLAGS   += -D_GNU_SOURCE
-CPPFLAGS   += -W -Wall -Werror
+CPPFLAGS   += -W -Wall
 ARFLAGS     = crus
 MAKEFLAGS   = --no-print-directory --silent
 

README.md

@@ -74,6 +74,12 @@ Generic Functions
   Very simple `rsync()` to copy files files and directories
   recursively.
 
+- `tempfile()`
+
+  Secure replacement for `tmpfile()`.  Creates an invisible temporary
+  file in `/tmp` that is removed when the returned %FILE pointer is
+  closed.
+
 
 OpenBSD Functions
 -----------------

tempfile.c

@@ -21,6 +21,11 @@
 #include <stdio.h>		/* fdopen() */
 #include <sys/stat.h>		/* umask() */
 
+#ifndef  O_TMPFILE		/* Too old GLIBC or kernel */
+#warning O_TMPFILE missing on your system, tempfile() may not work!
+#define  O_TMPFILE 020200000	/* Define and let it fail at runtime */
+#endif
+
 /**
  * tempfile - A secure tmpfile() replacement
  *
@@ -29,6 +34,8 @@
  * for security.  When the %FILE is fclose()'ed the file contents is
  * lost.  The file is hidden in the %_PATH_TMP directory on the system.
  *
+ * This function requires Linux 3.11, or later, due to %O_TMPFILE.
+ *
  * Returns:
  * An open %FILE pointer, or %NULL on error.
  */