[SCSI] libfc: Add routine to copy data from a buffer to a SG list

When handling the multi-frame responses of fc pass-thru requests,
a code segment similar to fc_fcp_recv_data (routine to receive
inbound SCSI data) is used in the response handler. This patch
is to add a routine, called fc_copy_buffer_to_sglist(), to handle
the common function of copying data from a buffer to a scatter-
gather list in order to avoid code duplication.

Signed-off-by: Robert Love <robert.w.love@intel.com>
Signed-off-by: James Bottomley <James.Bottomley@suse.de>

1 files changed, 60 insertions, 0 deletions

diff --git a/drivers/scsi/libfc/fc_libfc.c b/drivers/scsi/libfc/fc_libfc.c
index 01418ae8cb84..295eafb0316f 100644
--- a/drivers/scsi/libfc/fc_libfc.c
+++ b/drivers/scsi/libfc/fc_libfc.c
@@ -72,3 +72,63 @@ static void __exit libfc_exit(void)
         fc_destroy_rport();
 }
 module_exit(libfc_exit);
+
+/**
+ * fc_copy_buffer_to_sglist() - This routine copies the data of a buffer
+ *                              into a scatter-gather list (SG list).
+ *
+ * @buf: pointer to the data buffer.
+ * @len: the byte-length of the data buffer.
+ * @sg: pointer to the pointer of the SG list.
+ * @nents: pointer to the remaining number of entries in the SG list.
+ * @offset: pointer to the current offset in the SG list.
+ * @km_type: dedicated page table slot type for kmap_atomic.
+ * @crc: pointer to the 32-bit crc value.
+ *       If crc is NULL, CRC is not calculated.
+ */
+u32 fc_copy_buffer_to_sglist(void *buf, size_t len,
+                             struct scatterlist *sg,
+                             u32 *nents, size_t *offset,
+                             enum km_type km_type, u32 *crc)
+{
+        size_t remaining = len;
+        u32 copy_len = 0;
+
+        while (remaining > 0 && sg) {
+                size_t off, sg_bytes;
+                void *page_addr;
+
+                if (*offset >= sg->length) {
+                        /*
+                         * Check for end and drop resources
+                         * from the last iteration.
+                         */
+                        if (!(*nents))
+                                break;
+                        --(*nents);
+                        *offset -= sg->length;
+                        sg = sg_next(sg);
+                        continue;
+                }
+                sg_bytes = min(remaining, sg->length - *offset);
+
+                /*
+                 * The scatterlist item may be bigger than PAGE_SIZE,
+                 * but we are limited to mapping PAGE_SIZE at a time.
+                 */
+                off = *offset + sg->offset;
+                sg_bytes = min(sg_bytes,
+                               (size_t)(PAGE_SIZE - (off & ~PAGE_MASK)));
+                page_addr = kmap_atomic(sg_page(sg) + (off >> PAGE_SHIFT),
+                                        km_type);
+                if (crc)
+                        *crc = crc32(*crc, buf, sg_bytes);
+                memcpy((char *)page_addr + (off & ~PAGE_MASK), buf, sg_bytes);
+                kunmap_atomic(page_addr, km_type);
+                buf += sg_bytes;
+                *offset += sg_bytes;
+                remaining -= sg_bytes;
+                copy_len += sg_bytes;
+        }
+        return copy_len;
+}