[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 <fujita.tomonori@lab.ntt.co.jp>
Signed-off-by: James Bottomley <James.Bottomley@SteelEye.com>

1 files changed, 38 insertions, 0 deletions

diff --git a/drivers/scsi/scsi_lib.c b/drivers/scsi/scsi_lib.c
index 1f5a07bf2a75..70454b4e8485 100644
--- a/drivers/scsi/scsi_lib.c
+++ b/drivers/scsi/scsi_lib.c
@@ -2290,3 +2290,41 @@ void scsi_kunmap_atomic_sg(void *virt)
         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);