blktrace: avoid device duplication

Fixup for bz 501457.

Problem:
If the device list file contains the same device as supplied on the command line, blktrace stops immediately and further I/O tracing is impossible.

Bug: device duplication in the devpaths ends with programm termination (BLKTRACESETUP ioctl returns error) while resources (open files in debugfs) are not released.

Solution:
Make sure devices are not duplicated in devpaths pool.

Signed-off-by Edward Shishkin <[email protected]>

---
 blktrace.c |    9 +++++++++
 1 file changed, 9 insertions(+)

blktrace.c +9 -0

@@ -1200,8 +1200,17 @@ static int add_devpath(char *path)
 {
 	int fd;
 	struct devpath *dpp;
+	struct list_head *p;
 
 	/*
+	 * Verify device is not duplicated
+	 */
+	__list_for_each(p, &devpaths) {
+	       struct devpath *tmp = list_entry(p, struct devpath, head);
+	       if (!strcmp(tmp->path, path))
+		        return 0;
+	}
+	/*
 	 * Verify device is valid before going too far
 	 */
 	fd = my_open(path, O_RDONLY | O_NONBLOCK);