libutil: determine base device address in case of given partition

util_sys_get_dev_addr() returns the device address for a given blockdevice.
This does not work for partitions but some tools rely on the ability to get
the device address for partitions.

Add code that first determines the base device for a partition.

Fixes: 6014d07 ("dasdview/libdasd/zipl: Use util_sys_get_dev_addr() instead of u2s_getbusid()")
Signed-off-by: Stefan Haberland <sth@linux.ibm.com>
Reviewed-by: Jan Hoeppner <hoeppner@linux.ibm.com>
Reviewed-by: Philipp Rudo <prudo@linux.ibm.com>
Signed-off-by: Jan Höppner <hoeppner@linux.ibm.com>

libutil/util_sys.c

@@ -141,13 +141,17 @@ int util_sys_get_dev_addr(const char *dev, char *addr)
 	unsigned int maj, min;
 	struct stat s;
 	ssize_t len;
+	dev_t base;
 	char *path;
 
 	if (stat(dev, &s) != 0)
 		return -1;
 
-	maj = major(s.st_rdev);
-	min = minor(s.st_rdev);
+	if (util_sys_get_base_dev(s.st_rdev, &base))
+		return -1;
+
+	maj = major(base);
+	min = minor(base);
 
 	if (S_ISBLK(s.st_mode))
 		path = util_path_sysfs("dev/block/%u:%u/device", maj, min);