[SCSI] st: add st_scsi_execute helper function

st_scsi_execute is a helper function to perform SCSI commands
involving data transfer between user and kernel space (st_read and
st_write).

It's the future plan to combine this with st_scsi_kern_execute helper
function.
Signed-off-by: FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp>
Acked-by: Kai Makisara <Kai.Makisara@kolumbus.fi>
Signed-off-by: James Bottomley <James.Bottomley@HansenPartnership.com>

drivers/scsi/st.c

@@ -475,6 +475,60 @@ static void st_release_request(struct st_request *streq)
 	kfree(streq);
 }
 
+static void st_scsi_execute_end(struct request *req, int uptodate)
+{
+	struct st_request *SRpnt = req->end_io_data;
+	struct scsi_tape *STp = SRpnt->stp;
+
+	STp->buffer->cmdstat.midlevel_result = SRpnt->result = req->errors;
+	STp->buffer->cmdstat.residual = req->data_len;
+
+	if (SRpnt->waiting)
+		complete(SRpnt->waiting);
+
+	blk_rq_unmap_user(SRpnt->bio);
+	__blk_put_request(req->q, req);
+}
+
+static int st_scsi_execute(struct st_request *SRpnt, const unsigned char *cmd,
+			   int data_direction, void *buffer, unsigned bufflen,
+			   int timeout, int retries)
+{
+	struct request *req;
+	struct rq_map_data *mdata = &SRpnt->stp->buffer->map_data;
+	int err = 0;
+	int write = (data_direction == DMA_TO_DEVICE);
+
+	req = blk_get_request(SRpnt->stp->device->request_queue, write,
+			      GFP_KERNEL);
+	if (!req)
+		return DRIVER_ERROR << 24;
+
+	req->cmd_type = REQ_TYPE_BLOCK_PC;
+	req->cmd_flags |= REQ_QUIET;
+
+	mdata->null_mapped = 1;
+
+	err = blk_rq_map_user(req->q, req, mdata, NULL, bufflen, GFP_KERNEL);
+	if (err) {
+		blk_put_request(req);
+		return DRIVER_ERROR << 24;
+	}
+
+	SRpnt->bio = req->bio;
+	req->cmd_len = COMMAND_SIZE(cmd[0]);
+	memset(req->cmd, 0, BLK_MAX_CDB);
+	memcpy(req->cmd, cmd, req->cmd_len);
+	req->sense = SRpnt->sense;
+	req->sense_len = 0;
+	req->timeout = timeout;
+	req->retries = retries;
+	req->end_io_data = SRpnt;
+
+	blk_execute_rq_nowait(req->q, NULL, req, 1, st_scsi_execute_end);
+	return 0;
+}
+
 /* Do the scsi command. Waits until command performed if do_wait is true.
    Otherwise write_behind_check() is used to check that the command
    has finished. */

drivers/scsi/st.h

@@ -29,6 +29,7 @@ struct st_request {
 	int result;
 	struct scsi_tape *stp;
 	struct completion *waiting;
+	struct bio *bio;
 };
 
 /* The tape buffer descriptor. */