block: kill rq->data

Now that all block request data transfer is done via bio, rq->data
isn't used.  Kill it.

While at it, make the roles of rq->special and buffer clear.

[ Impact: drop now unncessary field from struct request ]
Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: Boaz Harrosh <bharrosh@panasas.com>

block/blk-core.c

@@ -189,10 +189,9 @@ void blk_dump_rq_flags(struct request *rq, char *msg)
 						(unsigned long long)rq->sector,
 						rq->nr_sectors,
 						rq->current_nr_sectors);
-	printk(KERN_INFO "  bio %p, biotail %p, buffer %p, data %p, len %u\n",
+	printk(KERN_INFO "  bio %p, biotail %p, buffer %p, len %u\n",
 						rq->bio, rq->biotail,
-						rq->buffer, rq->data,
-						rq->data_len);
+						rq->buffer, rq->data_len);
 
 	if (blk_pc_request(rq)) {
 		printk(KERN_INFO "  cdb: ");

block/blk-map.c

@@ -156,7 +156,7 @@ int blk_rq_map_user(struct request_queue *q, struct request *rq,
 	if (!bio_flagged(bio, BIO_USER_MAPPED))
 		rq->cmd_flags |= REQ_COPY_USER;
 
-	rq->buffer = rq->data = NULL;
+	rq->buffer = NULL;
 	return 0;
 unmap_rq:
 	blk_rq_unmap_user(bio);
@@ -235,7 +235,7 @@ int blk_rq_map_user_iov(struct request_queue *q, struct request *rq,
 	blk_queue_bounce(q, &bio);
 	bio_get(bio);
 	blk_rq_bio_prep(q, rq, bio);
-	rq->buffer = rq->data = NULL;
+	rq->buffer = NULL;
 	return 0;
 }
 EXPORT_SYMBOL(blk_rq_map_user_iov);
@@ -313,7 +313,7 @@ int blk_rq_map_kern(struct request_queue *q, struct request *rq, void *kbuf,
 
 	blk_rq_bio_prep(q, rq, bio);
 	blk_queue_bounce(q, &rq->bio);
-	rq->buffer = rq->data = NULL;
+	rq->buffer = NULL;
 	return 0;
 }
 EXPORT_SYMBOL(blk_rq_map_kern);

block/scsi_ioctl.c

@@ -500,7 +500,6 @@ static int __blk_send_generic(struct request_queue *q, struct gendisk *bd_disk,
 
 	rq = blk_get_request(q, WRITE, __GFP_WAIT);
 	rq->cmd_type = REQ_TYPE_BLOCK_PC;
-	rq->data = NULL;
 	rq->data_len = 0;
 	rq->extra_len = 0;
 	rq->timeout = BLK_DEFAULT_SG_TIMEOUT;

drivers/scsi/scsi_lib.c

@@ -1088,7 +1088,6 @@ int scsi_setup_blk_pc_cmnd(struct scsi_device *sdev, struct request *req)
 			return ret;
 	} else {
 		BUG_ON(req->data_len);
-		BUG_ON(req->data);
 
 		memset(&cmd->sdb, 0, sizeof(cmd->sdb));
 		req->buffer = NULL;

include/linux/blkdev.h

@@ -211,8 +211,8 @@ struct request {
 
 	unsigned short ioprio;
 
-	void *special;
-	char *buffer;
+	void *special;		/* opaque pointer available for LLD use */
+	char *buffer;		/* kaddr of the current segment if available */
 
 	int tag;
 	int errors;
@@ -229,7 +229,6 @@ struct request {
 	unsigned int data_len;
 	unsigned int extra_len;	/* length of alignment and padding */
 	unsigned int sense_len;
-	void *data;
 	void *sense;
 
 	unsigned long deadline;