libata: implement ata_qc_raw_nbytes()

Implement ata_qc_raw_nbytes() which determines the raw user-requested
size of a PC command.

Signed-off-by: Tejun Heo <[e-mail]>
Signed-off-by: Jeff Garzik <[e-mail]>

drivers/ata/libata-scsi.c

···
 	return qc;
 }
 
+static void ata_qc_set_pc_nbytes(struct ata_queued_cmd *qc)
+{
+	struct scsi_cmnd *scmd = qc->scsicmd;
+
+	qc->extrabytes = scmd->request->extra_len;
+	qc->nbytes = scsi_bufflen(scmd) + qc->extrabytes;
+}
+
 /**
  *	ata_dump_status - user friendly display of error info
  *	@id: id of the port in question
···
 	}
 
 	qc->tf.command = ATA_CMD_PACKET;
-	qc->nbytes = scsi_bufflen(scmd) + scmd->request->extra_len;
+	ata_qc_set_pc_nbytes(qc);
 
 	/* check whether ATAPI DMA is safe */
 	if (!using_pio && ata_check_atapi_dma(qc))
···
 	 * want to set it properly, and for DMA where it is
 	 * effectively meaningless.
 	 */
-	nbytes = min(scmd->request->data_len, (unsigned int)63 * 1024);
+	nbytes = min(ata_qc_raw_nbytes(qc), (unsigned int)63 * 1024);
 
 	/* Most ATAPI devices which honor transfer chunk size don't
 	 * behave according to the spec when odd chunk size which
···
 	 * TODO: find out if we need to do more here to
 	 *       cover scatter/gather case.
 	 */
-	qc->nbytes = scsi_bufflen(scmd) + scmd->request->extra_len;
+	ata_qc_set_pc_nbytes(qc);
 
 	/* request result TF and be quiet about device error */
 	qc->flags |= ATA_QCFLAG_RESULT_TF | ATA_QCFLAG_QUIET;

include/linux/libata.h

···
 	unsigned int		sect_size;
 
 	unsigned int		nbytes;
+	unsigned int		extrabytes;
 	unsigned int		curbytes;
 
 	struct scatterlist	*cursg;
···
 	return NULL;
 }
 
+static inline unsigned int ata_qc_raw_nbytes(struct ata_queued_cmd *qc)
+{
+	return qc->nbytes - min(qc->extrabytes, qc->nbytes);
+}
+
 static inline void ata_tf_init(struct ata_device *dev, struct ata_taskfile *tf)
 {
 	memset(tf, 0, sizeof(*tf));
···
 	qc->flags = 0;
 	qc->cursg = NULL;
 	qc->cursg_ofs = 0;
-	qc->nbytes = qc->curbytes = 0;
+	qc->nbytes = qc->extrabytes = qc->curbytes = 0;
 	qc->n_elem = 0;
 	qc->err_mask = 0;
 	qc->sect_size = ATA_SECT_SIZE;