udf: Fix free space reporting for metadata and virtual partitions

Free space on filesystems with metadata or virtual partition maps
currently gets misreported. This is because these partitions are just
remapped onto underlying real partitions from which keep track of free
blocks. Take this remapping into account when counting free blocks as
well.
Reviewed-by: Pali Rohár <pali.rohar@gmail.com>
Reported-by: Pali Rohár <pali.rohar@gmail.com>
Signed-off-by: Jan Kara <jack@suse.cz>

fs/udf/super.c

@@ -2492,17 +2492,29 @@ static unsigned int udf_count_free_table(struct super_block *sb,
 static unsigned int udf_count_free(struct super_block *sb)
 {
 	unsigned int accum = 0;
-	struct udf_sb_info *sbi;
+	struct udf_sb_info *sbi = UDF_SB(sb);
 	struct udf_part_map *map;
+	unsigned int part = sbi->s_partition;
+	int ptype = sbi->s_partmaps[part].s_partition_type;
+
+	if (ptype == UDF_METADATA_MAP25) {
+		part = sbi->s_partmaps[part].s_type_specific.s_metadata.
+							s_phys_partition_ref;
+	} else if (ptype == UDF_VIRTUAL_MAP15 || ptype == UDF_VIRTUAL_MAP20) {
+		/*
+		 * Filesystems with VAT are append-only and we cannot write to
+ 		 * them. Let's just report 0 here.
+		 */
+		return 0;
+	}
 
-	sbi = UDF_SB(sb);
 	if (sbi->s_lvid_bh) {
 		struct logicalVolIntegrityDesc *lvid =
 			(struct logicalVolIntegrityDesc *)
 			sbi->s_lvid_bh->b_data;
-		if (le32_to_cpu(lvid->numOfPartitions) > sbi->s_partition) {
+		if (le32_to_cpu(lvid->numOfPartitions) > part) {
 			accum = le32_to_cpu(
-					lvid->freeSpaceTable[sbi->s_partition]);
+					lvid->freeSpaceTable[part]);
 			if (accum == 0xFFFFFFFF)
 				accum = 0;
 		}
@@ -2511,7 +2523,7 @@ static unsigned int udf_count_free(struct super_block *sb)
 	if (accum)
 		return accum;
 
-	map = &sbi->s_partmaps[sbi->s_partition];
+	map = &sbi->s_partmaps[part];
 	if (map->s_partition_flags & UDF_PART_FLAG_UNALLOC_BITMAP) {
 		accum += udf_count_free_bitmap(sb,
 					       map->s_uspace.s_bitmap);