btrfs-progs: mkfs: print label of existing filesystem

For better identification also print the label (if set) found on the
image when -f is not used:

  $ mkfs.btrfs --label=TEST img
  $ mkfs.btrfs img
  ERROR: img appears to contain an existing filesystem (type=btrfs, label=TEST)
  ERROR: use the -f option to force overwrite of img

Signed-off-by: David Sterba <dsterba@suse.com>

Author: kdave

mkfs/common.c

@@ -1049,7 +1049,12 @@ static int check_overwrite(const char *device)
 	}
 
 	if (!blkid_probe_lookup_value(pr, "TYPE", &type, NULL)) {
-		error("%s appears to contain an existing filesystem (%s)", device, type);
+		const char *label = NULL;
+
+		blkid_probe_lookup_value(pr, "LABEL", &label, NULL);
+
+		error("%s appears to contain an existing filesystem (type=%s%s%s)",
+		      device, type, (label ? ", label=" : ""), (label ? label : ""));
 	} else if (!blkid_probe_lookup_value(pr, "PTTYPE", &type, NULL)) {
 		error("%s appears to contain a partition table (%s)", device, type);
 	} else {