PERFORCE change 133646 for review

[Scott Long]

http://perforce.freebsd.org/chv.cgi?CH=133646

Change 133646 by scottl at scottl-ix on 2008/01/19 09:12:20

	Don't spam bp->bio_data while doing a re-aligned I/O operation.
	For reasons I don't understand, it causes problems during writes,
	but not during reads.

Affected files ...

.. //depot/projects/xen31-xenbus/sys/dev/xen/blkfront/blkfront.c#3 edit

Differences ...

==== //depot/projects/xen31-xenbus/sys/dev/xen/blkfront/blkfront.c#3 (text+ko) ====

@@ -656,6 +656,7 @@
  */
 static int blkif_queue_request(struct bio *bp)
 {
+	caddr_t alignbuf;
 	unsigned long  	buffer_ma;
 	blkif_request_t     *ring_req;
 	unsigned long id;
@@ -683,16 +684,18 @@
 			PAGE_SIZE;
 		caddr_t newbuf = malloc(bp->bio_bcount + align, M_DEVBUF, 
 					M_NOWAIT);
-		caddr_t alignbuf = (char *)roundup2((u_long)newbuf, align);
+
+		alignbuf = (char *)roundup2((u_long)newbuf, align);
 
 		/* save a copy of the current buffer */
-		bp->bio_driver1 = bp->bio_data;
+		bp->bio_driver1 = newbuf;
+		bp->bio_driver2 = alignbuf;
 
 		/* Copy the data for a write */
 		if (bp->bio_cmd == BIO_WRITE)
 			bcopy(bp->bio_data, alignbuf, bp->bio_bcount);
-		bp->bio_data = alignbuf;
-	}
+	} else
+		alignbuf = bp->bio_data;
 	
 	/* Fill out a communications ring structure. */
 	ring_req 	         = RING_GET_REQUEST(&info->ring, 
@@ -711,7 +714,7 @@
 					 * chaining is not supported.
 					 */
 
-	buffer_ma = vtomach(bp->bio_data);
+	buffer_ma = vtomach(alignbuf);
 	fsect = (buffer_ma & PAGE_MASK) >> XBD_SECTOR_SHFT;
 	lsect = fsect + (bp->bio_bcount >> XBD_SECTOR_SHFT) - 1;
 	/* install a grant reference. */
@@ -823,14 +826,15 @@
 		switch (bret->operation) {
 		case BLKIF_OP_READ:
 			/* had an unaligned buffer that needs to be copied */
-			if (bp->bio_driver1)
-				bcopy(bp->bio_data, bp->bio_driver1, bp->bio_bcount);
+			if (bp->bio_driver1) {
+				bcopy(bp->bio_driver2, bp->bio_data, bp->bio_bcount);
+				bp->bio_driver1 = NULL;
+			}
 		case BLKIF_OP_WRITE:
 
 			/* free the copy buffer */
 			if (bp->bio_driver1) {
-				free(bp->bio_data, M_DEVBUF);
-				bp->bio_data = bp->bio_driver1;
+				free(bp->bio_driver1, M_DEVBUF);
 				bp->bio_driver1 = NULL;
 			}