udf: Add read-only support for 2.50 UDF media

This patch implements parsing of metadata partitions and reading of Metadata
File thus allowing to read UDF 2.50 media. Error resilience is implemented
through accessing the Metadata Mirror File in case the data the Metadata File
cannot be read. The patch is based on the original patch by Sebastian Manciulea
<manciuleas@yahoo.com> and Mircea Fedoreanu <mirceaf_spl@yahoo.com>.

Signed-off-by: Sebastian Manciulea <manciuleas@yahoo.com>
Signed-off-by: Mircea Fedoreanu <mirceaf_spl@yahoo.com>
Signed-off-by: Jan Kara <jack@suse.cz>
diff --git a/fs/udf/udfdecl.h b/fs/udf/udfdecl.h
index 2cb2f5d..30f664a 100644
--- a/fs/udf/udfdecl.h
+++ b/fs/udf/udfdecl.h
@@ -177,6 +177,8 @@
 				      uint32_t);
 extern uint32_t udf_get_pblock_spar15(struct super_block *, uint32_t, uint16_t,
 				      uint32_t);
+extern uint32_t udf_get_pblock_meta25(struct super_block *, uint32_t, uint16_t,
+					  uint32_t);
 extern int udf_relocate_blocks(struct super_block *, long, long *);
 
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