new "mountpoint" export option.

2 files changed, 35 insertions, 1 deletions

diff --git a/support/misc/Makefile b/support/misc/Makefile
index b2f73f8..c738564 100644
--- a/support/misc/Makefile
+++ b/support/misc/Makefile
@@ -3,7 +3,7 @@
 #
 
 LIBNAME	= libmisc.a
-OBJS	= tcpwrapper.o from_local.o
+OBJS	= tcpwrapper.o from_local.o mountpoint.o
 
 include $(TOP)rules.mk
 
diff --git a/support/misc/mountpoint.c b/support/misc/mountpoint.c
new file mode 100644
index 0000000..6d0f34e
--- /dev/null
+++ b/support/misc/mountpoint.c
@@ -0,0 +1,34 @@
+
+/*
+ * check if a given path is a mountpoint 
+ */
+
+#include <string.h>
+#include <malloc.h>
+#include <sys/stat.h>
+
+int
+is_mountpoint(char *path)
+{
+	/* Check if 'path' is a current mountpoint.
+	 * Possibly we should also check it is the mountpoint of the 
+	 * filesystem holding the target directory, but there doesn't
+	 * seem a lot of point.
+	 *
+	 * We deem it to be a mountpoint if appending a ".." gives a different
+	 * device or the same inode number.
+	 */
+	char *dotdot;
+	struct stat stb, pstb;
+
+	dotdot = malloc(strlen(path)+4);
+	strcat(strcpy(dotdot, path), "/..");
+	if (lstat(path, &stb) != 0 ||
+	    lstat(dotdot, &pstb) != 0)
+		return 0;
+
+	if (stb.st_dev != pstb.st_dev
+	    || stb.st_ino == pstb.st_ino)
+		return 1;
+	return 0;
+}