I'm tired of seeing this done incorrectly and non-portably, so add a

flopen(3) function which reliably opens and locks a file.

MFC after:	3 weeks

1 files changed, 91 insertions, 0 deletions

diff --git a/lib/libutil/flopen.c b/lib/libutil/flopen.c
new file mode 100644
index 0000000..66d4e47
--- /dev/null
+++ b/lib/libutil/flopen.c
@@ -0,0 +1,91 @@
+/*-
+ * Copyright (c) 2007 Dag-Erling Coïdan Smørgrav
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer
+ *    in this position and unchanged.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
+ * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
+ * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+ * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+ * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
+ * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+ * SUCH DAMAGE.
+ *
+ * $Id$
+ */
+
+#include <sys/cdefs.h>
+__FBSDID("$FreeBSD$");
+
+#include <sys/stat.h>
+
+#include <errno.h>
+#include <fcntl.h>
+#include <stdarg.h>
+
+int
+flopen(const char *path, int flags, ...)
+{
+	struct stat sb, fsb;
+	mode_t mode;
+	int fd, serrno;
+
+#ifdef O_EXLOCK
+	flags &= ~O_EXLOCK;
+#endif
+
+	if (flags & O_CREAT) {
+		va_list ap;
+
+		va_start(ap, flags);
+		mode = va_arg(ap, int); /* mode_t promoted to int */
+		va_end(ap);
+	} else {
+		mode = 0;
+	}
+
+	for (;;) {
+		if ((fd = open(path, flags, mode)) == -1)
+			/* non-existent or no access */
+			return (-1);
+		if (flock(fd, LOCK_EX) == -1) {
+			/* unsupported or interrupted */
+			serrno = errno;
+			close(fd);
+			errno = serrno;
+			return (-1);
+		}
+		if (stat(path, &sb) == -1) {
+			/* disappeared from under our feet */
+			close(fd);
+			continue;
+		}
+		if (fstat(fd, &fsb) == -1) {
+			/* can't happen [tm] */
+			serrno = errno;
+			close(fd);
+			errno = serrno;
+			return (-1);
+		}
+		if (sb.st_dev != fsb.st_dev ||
+		    sb.st_ino != fsb.st_ino) {
+			/* changed under our feet */
+			close(fd);
+			continue;
+		}
+		return (fd);
+	}
+}