[SCSI] scsi_lib: add scatter/gather data buffer accessors

This adds a set of accessors for the scsi data buffer. This is in
preparation for chaining sg lists and bidirectional requests (and
possibly, the mid-layer dma mapping).

Signed-off-by: FUJITA Tomonori <[e-mail]>
Signed-off-by: James Bottomley <[e-mail]>

drivers/scsi/scsi_lib.c

···
 	kunmap_atomic(virt, KM_BIO_SRC_IRQ);
 }
 EXPORT_SYMBOL(scsi_kunmap_atomic_sg);
+
+/**
+ * scsi_dma_map - perform DMA mapping against command's sg lists
+ * @cmd:	scsi command
+ *
+ * Returns the number of sg lists actually used, zero if the sg lists
+ * is NULL, or -ENOMEM if the mapping failed.
+ */
+int scsi_dma_map(struct scsi_cmnd *cmd)
+{
+	int nseg = 0;
+
+	if (scsi_sg_count(cmd)) {
+		struct device *dev = cmd->device->host->shost_gendev.parent;
+
+		nseg = dma_map_sg(dev, scsi_sglist(cmd), scsi_sg_count(cmd),
+				  cmd->sc_data_direction);
+		if (unlikely(!nseg))
+			return -ENOMEM;
+	}
+	return nseg;
+}
+EXPORT_SYMBOL(scsi_dma_map);
+
+/**
+ * scsi_dma_unmap - unmap command's sg lists mapped by scsi_dma_map
+ * @cmd:	scsi command
+ */
+void scsi_dma_unmap(struct scsi_cmnd *cmd)
+{
+	if (scsi_sg_count(cmd)) {
+		struct device *dev = cmd->device->host->shost_gendev.parent;
+
+		dma_unmap_sg(dev, scsi_sglist(cmd), scsi_sg_count(cmd),
+			     cmd->sc_data_direction);
+	}
+}
+EXPORT_SYMBOL(scsi_dma_unmap);

include/scsi/scsi_cmnd.h

···
 extern struct scatterlist *scsi_alloc_sgtable(struct scsi_cmnd *, gfp_t);
 extern void scsi_free_sgtable(struct scatterlist *, int);
 
+extern int scsi_dma_map(struct scsi_cmnd *cmd);
+extern void scsi_dma_unmap(struct scsi_cmnd *cmd);
+
+#define scsi_sg_count(cmd) ((cmd)->use_sg)
+#define scsi_sglist(cmd) ((struct scatterlist *)(cmd)->request_buffer)
+#define scsi_bufflen(cmd) ((cmd)->request_bufflen)
+
+static inline void scsi_set_resid(struct scsi_cmnd *cmd, int resid)
+{
+	cmd->resid = resid;
+}
+
+static inline int scsi_get_resid(struct scsi_cmnd *cmd)
+{
+	return cmd->resid;
+}
+
+#define scsi_for_each_sg(cmd, sg, nseg, __i)			\
+	for (__i = 0, sg = scsi_sglist(cmd); __i < (nseg); __i++, (sg)++)
+
 #endif /* _SCSI_SCSI_CMND_H */