1 files changed, 57 insertions, 0 deletions

diff --git a/drivers/scsi/scsi_lib.c b/drivers/scsi/scsi_lib.c
index 7b0f9a3810d2..57453ca09700 100644
--- a/drivers/scsi/scsi_lib.c
+++ b/drivers/scsi/scsi_lib.c
@@ -2350,3 +2350,60 @@ scsi_target_unblock(struct device *dev)
                 device_for_each_child(dev, NULL, target_unblock);
 }
 EXPORT_SYMBOL_GPL(scsi_target_unblock);
+
+/**
+ * scsi_kmap_atomic_sg - find and atomically map an sg-elemnt
+ * @sg:         scatter-gather list
+ * @sg_count:   number of segments in sg
+ * @offset:     offset in bytes into sg, on return offset into the mapped area
+ * @len:        bytes to map, on return number of bytes mapped
+ *
+ * Returns virtual address of the start of the mapped page
+ */
+void *scsi_kmap_atomic_sg(struct scatterlist *sg, int sg_count,
+                          size_t *offset, size_t *len)
+{
+        int i;
+        size_t sg_len = 0, len_complete = 0;
+        struct page *page;
+
+        for (i = 0; i < sg_count; i++) {
+                len_complete = sg_len; /* Complete sg-entries */
+                sg_len += sg[i].length;
+                if (sg_len > *offset)
+                        break;
+        }
+
+        if (unlikely(i == sg_count)) {
+                printk(KERN_ERR "%s: Bytes in sg: %u, requested offset %u, elements %d\n",
+                       __FUNCTION__, sg_len, *offset, sg_count);
+                WARN_ON(1);
+                return NULL;
+        }
+
+        /* Offset starting from the beginning of first page in this sg-entry */
+        *offset = *offset - len_complete + sg[i].offset;
+
+        /* Assumption: contiguous pages can be accessed as "page + i" */
+        page = nth_page(sg[i].page, (*offset >> PAGE_SHIFT));
+        *offset &= ~PAGE_MASK;
+
+        /* Bytes in this sg-entry from *offset to the end of the page */
+        sg_len = PAGE_SIZE - *offset;
+        if (*len > sg_len)
+                *len = sg_len;
+
+        return kmap_atomic(page, KM_BIO_SRC_IRQ);
+}
+EXPORT_SYMBOL(scsi_kmap_atomic_sg);
+
+/**
+ * scsi_kunmap_atomic_sg - atomically unmap a virtual address, previously
+ *                         mapped with scsi_kmap_atomic_sg
+ * @virt:       virtual address to be unmapped
+ */
+void scsi_kunmap_atomic_sg(void *virt)
+{
+        kunmap_atomic(virt, KM_BIO_SRC_IRQ);
+}
+EXPORT_SYMBOL(scsi_kunmap_atomic_sg);