block: introduce blk_rq_is_passthrough

This can be used to check for fs vs non-fs requests and basically
removes all knowledge of BLOCK_PC specific from the block layer,
as well as preparing for removing the cmd_type field in struct request.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jens Axboe <axboe@fb.com>

drivers/scsi/sun3_scsi.c

@@ -260,7 +260,7 @@ static int sun3scsi_dma_xfer_len(struct NCR5380_hostdata *hostdata,
 {
 	int wanted_len = cmd->SCp.this_residual;
 
-	if (wanted_len < DMA_MIN_SIZE || cmd->request->cmd_type != REQ_TYPE_FS)
+	if (wanted_len < DMA_MIN_SIZE || blk_rq_is_passthrough(cmd->request))
 		return 0;
 
 	return wanted_len;