internals: added tpax_tmpfile().

2 files changed, 80 insertions, 0 deletions

diff --git a/src/internal/tpax_tmpfile_impl.c b/src/internal/tpax_tmpfile_impl.c
new file mode 100644
index 0000000..0c0bcc1
--- /dev/null
+++ b/src/internal/tpax_tmpfile_impl.c
@@ -0,0 +1,74 @@
+/******************************************************/
+/*  tpax: a topological pax implementation            */
+/*  Copyright (C) 2020  Z. Gilboa                     */
+/*  Released under GPLv2 and GPLv3; see COPYING.TPAX. */
+/******************************************************/
+
+#define _GNU_SOURCE
+#include <fcntl.h>
+#include <stdlib.h>
+#include <unistd.h>
+#include <string.h>
+#include <stdio.h>
+
+/* mkostemp might be guarded by non-standard macros */
+/* unless HAVE_NO_MKOSTEMP, assume it is available */
+extern int mkstemp(char *);
+extern int mkostemp(char *, int);
+
+/* __fs_tmpfile() atomically provides a private tmpfile */
+static int tpax_tmpfile_by_framework(void)
+{
+#ifdef _MIDIPIX_ABI
+	extern int __fs_tmpfile(int);
+	return __fs_tmpfile(O_CLOEXEC);
+#else
+	return (-1);
+#endif
+}
+
+/* O_TMPFILE atomically provides a private tmpfile */
+static int tpax_tmpfile_by_kernel(void)
+{
+#ifdef O_TMPFILE
+	return open("/tmp",O_RDWR|O_TMPFILE|O_CLOEXEC,0);
+#else
+	return (-1);
+#endif
+}
+
+/* mk{o}stemp() provides a non-private tmpfile */
+static int tpax_mkostemp(char * tmplate)
+{
+	int fd;
+#ifdef HAVE_NO_MKOSTEMP
+	if ((fd = mkstemp(tmplate)) >= 0)
+		fcntl(fd,F_SETFD,FD_CLOEXEC);
+#else
+	fd = mkostemp(tmplate,O_CLOEXEC);
+#endif
+	return fd;
+}
+
+int tpax_tmpfile(void)
+{
+	int             fd;
+	unsigned        seed;
+	char            tmplate[64];
+
+	/* try with __fs_tmpfile() */
+	if ((fd = tpax_tmpfile_by_framework()) >= 0)
+		return fd;
+
+	/* try with O_TMPFILE */
+	if ((fd = tpax_tmpfile_by_kernel()) >= 0)
+		return fd;
+
+	/* fallback to mk{o}stemp */
+	seed = getpid();
+	memset(tmplate,0,sizeof(tmplate));
+	snprintf(tmplate,sizeof(tmplate),"/tmp/tpax_%d_%d_%d_XXXXXXXXXXXX",
+		getppid(),getpid(),rand_r(&seed));
+
+	return tpax_mkostemp(tmplate);
+}
diff --git a/src/internal/tpax_tmpfile_impl.h b/src/internal/tpax_tmpfile_impl.h
new file mode 100644
index 0000000..f146326
--- /dev/null
+++ b/src/internal/tpax_tmpfile_impl.h
@@ -0,0 +1,6 @@
+#ifndef TPAX_TMPFILE_IMPL_H
+#define TPAX_TMPFILE_IMPL_H
+
+int tpax_tmpfile(void);
+
+#endif