fiemap: Add new extent flag FIEMAP_EXTENT_SHARED

Some filesystems may allow multiple files to point to a particular
extent.  This patch adds flag FIEMAP_EXTENT_SHARED to denote extents
that are shared with other inodes.
Signed-off-by: Sunil Mushran <sunil.mushran@oracle.com>
Acked-by: Mark Fasheh <mfasheh@suse.com>
Signed-off-by: Joel Becker <joel.becker@oracle.com>

include/linux/fiemap.h

@@ -62,5 +62,7 @@ struct fiemap {
 #define FIEMAP_EXTENT_MERGED		0x00001000 /* File does not natively
 						    * support extents. Result
 						    * merged for efficiency. */
+#define FIEMAP_EXTENT_SHARED		0x00002000 /* Space shared with other
+						    * files. */
 
 #endif /* _LINUX_FIEMAP_H */