iomap: don't set FIEMAP_EXTENT_MERGED for extent based filesystems

Filesystems like XFS that use extents should not set the
FIEMAP_EXTENT_MERGED flag in the fiemap extent structures.  To allow
for both behaviors for the upcoming gfs2 usage split the iomap
type field into type and flags, and only set FIEMAP_EXTENT_MERGED if
the IOMAP_F_MERGED flag is set.  The flags field will also come in
handy for future features such as shared extents on reflink-enabled
file systems.
Reported-by: Andreas Gruenbacher <agruenba@redhat.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>
Acked-by: Darrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: Dave Chinner <david@fromorbit.com>

fs/iomap.c

@@ -428,9 +428,12 @@ static int iomap_to_fiemap(struct fiemap_extent_info *fi,
 		break;
 	}
 
+	if (iomap->flags & IOMAP_F_MERGED)
+		flags |= FIEMAP_EXTENT_MERGED;
+
 	return fiemap_fill_next_extent(fi, iomap->offset,
 			iomap->blkno != IOMAP_NULL_BLOCK ? iomap->blkno << 9: 0,
-			iomap->length, flags | FIEMAP_EXTENT_MERGED);
+			iomap->length, flags);
 
 }
 

include/linux/iomap.h

@@ -18,6 +18,11 @@ struct vm_fault;
 #define IOMAP_MAPPED	0x03	/* blocks allocated @blkno */
 #define IOMAP_UNWRITTEN	0x04	/* blocks allocated @blkno in unwritten state */
 
+/*
+ * Flags for iomap mappings:
+ */
+#define IOMAP_F_MERGED	0x01	/* contains multiple blocks/extents */
+
 /*
  * Magic value for blkno:
  */
@@ -27,7 +32,8 @@ struct iomap {
 	sector_t		blkno;	/* 1st sector of mapping, 512b units */
 	loff_t			offset;	/* file offset of mapping, bytes */
 	u64			length;	/* length of mapping, bytes */
-	int			type;	/* type of mapping */
+	u16			type;	/* type of mapping */
+	u16			flags;	/* flags for mapping */
 	struct block_device	*bdev;	/* block device for I/O */
 };