[PATCH 25/35] libfc: Add routine to copy data from a buffer to a SG list

[Robert Love <robert.w.love@intel.com>]

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>
---

 drivers/scsi/libfc/fc_fcp.c   |   56 +++++++-------------------------------
 drivers/scsi/libfc/fc_libfc.c |   60 +++++++++++++++++++++++++++++++++++++++++
 drivers/scsi/libfc/fc_libfc.h |    8 +++++
 3 files changed, 78 insertions(+), 46 deletions(-)

diff --git a/drivers/scsi/libfc/fc_fcp.c b/drivers/scsi/libfc/fc_fcp.c
index e4ff27e..a474773 100644
--- a/drivers/scsi/libfc/fc_fcp.c
+++ b/drivers/scsi/libfc/fc_fcp.c
@@ -324,7 +324,7 @@ static void fc_fcp_recv_data(struct fc_fcp_pkt *fsp, struct fc_frame *fp)
 	size_t len;
 	void *buf;
 	struct scatterlist *sg;
-	size_t remaining;
+	u32 nents;
 
 	fh = fc_frame_header_get(fp);
 	offset = ntohl(fh->fh_parm_offset);
@@ -348,55 +348,19 @@ static void fc_fcp_recv_data(struct fc_fcp_pkt *fsp, struct fc_frame *fp)
 	if (offset != fsp->xfer_len)
 		fsp->state |= FC_SRB_DISCONTIG;
 
-	crc = 0;
-	if (fr_flags(fp) & FCPHF_CRC_UNCHECKED)
-		crc = crc32(~0, (u8 *) fh, sizeof(*fh));
-
 	sg = scsi_sglist(sc);
-	remaining = len;
-
-	while (remaining > 0 && sg) {
-		size_t off;
-		void *page_addr;
-		size_t sg_bytes;
-
-		if (offset >= sg->length) {
-			offset -= sg->length;
-			sg = sg_next(sg);
-			continue;
-		}
-		sg_bytes = min(remaining, sg->length - offset);
+	nents = scsi_sg_count(sc);
 
-		/*
-		 * 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_SOFTIRQ0);
-		if (!page_addr)
-			break;		/* XXX panic? */
-
-		if (fr_flags(fp) & FCPHF_CRC_UNCHECKED)
-			crc = crc32(crc, buf, sg_bytes);
-		memcpy((char *)page_addr + (off & ~PAGE_MASK), buf,
-		       sg_bytes);
-
-		kunmap_atomic(page_addr, KM_SOFTIRQ0);
-		buf += sg_bytes;
-		offset += sg_bytes;
-		remaining -= sg_bytes;
-		copy_len += sg_bytes;
-	}
-
-	if (fr_flags(fp) & FCPHF_CRC_UNCHECKED) {
+	if (!(fr_flags(fp) & FCPHF_CRC_UNCHECKED)) {
+		copy_len = fc_copy_buffer_to_sglist(buf, len, sg, &nents,
+						    &offset, KM_SOFTIRQ0, NULL);
+	} else {
+		crc = crc32(~0, (u8 *) fh, sizeof(*fh));
+		copy_len = fc_copy_buffer_to_sglist(buf, len, sg, &nents,
+						    &offset, KM_SOFTIRQ0, &crc);
 		buf = fc_frame_payload_get(fp, 0);
-		if (len % 4) {
+		if (len % 4)
 			crc = crc32(crc, buf + len, 4 - (len % 4));
-			len += 4 - (len % 4);
-		}
 
 		if (~crc != le32_to_cpu(fr_crc(fp))) {
 crc_err:
diff --git a/drivers/scsi/libfc/fc_libfc.c b/drivers/scsi/libfc/fc_libfc.c
index 01418ae..295eafb 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;
+}
diff --git a/drivers/scsi/libfc/fc_libfc.h b/drivers/scsi/libfc/fc_libfc.h
index 0530149..e4b5e92 100644
--- a/drivers/scsi/libfc/fc_libfc.h
+++ b/drivers/scsi/libfc/fc_libfc.h
@@ -101,4 +101,12 @@ void fc_destroy_fcp(void);
  */
 const char *fc_els_resp_type(struct fc_frame *);
 
+/*
+ * Copies a buffer into an sg list
+ */
+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);
+
 #endif /* _FC_LIBFC_H_ */