[SCSI] fix write buffer length in scsi_req_map_sg()

sg's may have setup a the buffer with a different length than
the transfer length so we should be using the bufflen passed
in as the request's data len.
Signed-off-by: Mike Christie <michaelc@cs.wisc.edu>
Signed-off-by: James Bottomley <James.Bottomley@SteelEye.com>

drivers/scsi/scsi_lib.c

@@ -301,7 +301,7 @@ static int scsi_req_map_sg(struct request *rq, struct scatterlist *sgl,
 {
 	struct request_queue *q = rq->q;
 	int nr_pages = (bufflen + sgl[0].offset + PAGE_SIZE - 1) >> PAGE_SHIFT;
-	unsigned int data_len = 0, len, bytes, off;
+	unsigned int data_len = bufflen, len, bytes, off;
 	struct page *page;
 	struct bio *bio = NULL;
 	int i, err, nr_vecs = 0;
@@ -310,10 +310,15 @@ static int scsi_req_map_sg(struct request *rq, struct scatterlist *sgl,
 		page = sgl[i].page;
 		off = sgl[i].offset;
 		len = sgl[i].length;
-		data_len += len;
 
-		while (len > 0) {
+		while (len > 0 && data_len > 0) {
+			/*
+			 * sg sends a scatterlist that is larger than
+			 * the data_len it wants transferred for certain
+			 * IO sizes
+			 */
 			bytes = min_t(unsigned int, len, PAGE_SIZE - off);
+			bytes = min(bytes, data_len);
 
 			if (!bio) {
 				nr_vecs = min_t(int, BIO_MAX_PAGES, nr_pages);
@@ -345,12 +350,13 @@ static int scsi_req_map_sg(struct request *rq, struct scatterlist *sgl,
 
 			page++;
 			len -= bytes;
+			data_len -=bytes;
 			off = 0;
 		}
 	}
 
 	rq->buffer = rq->data = NULL;
-	rq->data_len = data_len;
+	rq->data_len = bufflen;
 	return 0;
 
 free_bios: