ext4: Support setting FMODE_CAN_ATOMIC_WRITE

FS needs to add the fmode capability in order to support atomic writes
during file open (refer kiocb_set_rw_flags()). Set this capability on
a regular file if ext4 can do atomic write.

Reviewed-by: John Garry <john.g.garry@oracle.com>
Reviewed-by: Darrick J. Wong <djwong@kernel.org>
Signed-off-by: Ritesh Harjani (IBM) <ritesh.list@gmail.com>
Signed-off-by: Darrick J. Wong <djwong@kernel.org>
Reviewed-by: Jan Kara <jack@suse.cz>

Author: riteshharjani

fs/ext4/file.c

@@ -898,6 +898,9 @@ static int ext4_file_open(struct inode *inode, struct file *filp)
 			return ret;
 	}
 
+	if (ext4_inode_can_atomic_write(inode))
+		filp->f_mode |= FMODE_CAN_ATOMIC_WRITE;
+
 	filp->f_mode |= FMODE_NOWAIT | FMODE_CAN_ODIRECT;
 	return dquot_file_open(inode, filp);
 }