ext4: add IOMAP_F_MERGED for non-extent based mapping

IOMAP_F_MERGED needs to be set in case of non-extent based mapping.
This is needed in later patches for conversion of ext4_fiemap to use iomap.
Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>
Reviewed-by: Jan Kara <jack@suse.cz>
Signed-off-by: Ritesh Harjani <riteshh@linux.ibm.com>
Link: https://lore.kernel.org/r/a4764c91c08c16d4d4a4b36defb2a08625b0e9b3.1582880246.git.riteshh@linux.ibm.comSigned-off-by: Theodore Ts'o <tytso@mit.edu>

fs/ext4/inode.c

@@ -3333,6 +3333,10 @@ static void ext4_set_iomap(struct inode *inode, struct iomap *iomap,
 	iomap->offset = (u64) map->m_lblk << blkbits;
 	iomap->length = (u64) map->m_len << blkbits;
 
+	if ((map->m_flags & EXT4_MAP_MAPPED) &&
+	    !ext4_test_inode_flag(inode, EXT4_INODE_EXTENTS))
+		iomap->flags |= IOMAP_F_MERGED;
+
 	/*
 	 * Flags passed to ext4_map_blocks() for direct I/O writes can result
 	 * in m_flags having both EXT4_MAP_MAPPED and EXT4_MAP_UNWRITTEN bits