sfdisk: don't use BLKRRPART to check loopdev usage

It seesm that kernel always returns EINVAL for BLKRRPART on loop
devices, we call the ioctl to check if nobody else uses the device.

Signed-off-by: Karel Zak <kzak@redhat.com>

disk-utils/sfdisk.c

@@ -44,6 +44,7 @@
 #include "blkdev.h"
 #include "all-io.h"
 #include "rpmatch.h"
+#include "loopdev.h"
 
 #include "libfdisk.h"
 #include "fdisk-list.h"
@@ -1083,7 +1084,8 @@ static int is_device_used(struct sfdisk *sf)
 	if (fd < 0)
 		return 0;
 
-	if (fstat(fd, &st) == 0 && S_ISBLK(st.st_mode))
+	if (fstat(fd, &st) == 0 && S_ISBLK(st.st_mode)
+	    && major(st.st_rdev) != LOOPDEV_MAJOR)
 		return ioctl(fd, BLKRRPART) != 0;
 #endif
 	return 0;