svn commit: r233465 - head/sys/dev/xen/blkfront

[Justin T. Gibbs]

Author: gibbs
Date: Sun Mar 25 14:20:43 2012
New Revision: 233465
URL: http://svn.freebsd.org/changeset/base/233465

Log:
  Correct failure to attach the PV block front device on Citrix
  XenServer configurations that advertise the multi-page ring extension,
  but only allow a single page of ring space.
  
  sys/dev/xen/blkfront/blkfront.c:
  	If only one page of ring space is being used, do not publish
  	in the XenStore the number of pages in use (1), via either
  	of the supported multi-page ring extension schemes.
  
  	Single page operation is the same with or without the
  	ring-page extension being negotiated.   Relying on the
  	legacy behavior avoids an incompatible difference in how
  	the two ring-page extension schemes that are out in the
  	wild, deal with the base case of a single page.  The
  	Amazon/Red Hat drivers use the same XenStore variable as
  	if the extension was not negotiated.  The Citrix drivers
  	assume the new ring reference XenStore variables will be
  	available
  
  Reported by:	Oliver Schonefeld <schonefeld at ids-mannheim.de>
  MFC after:	3 days

Modified:
  head/sys/dev/xen/blkfront/blkfront.c

Modified: head/sys/dev/xen/blkfront/blkfront.c
==============================================================================
--- head/sys/dev/xen/blkfront/blkfront.c	Sun Mar 25 13:20:38 2012	(r233464)
+++ head/sys/dev/xen/blkfront/blkfront.c	Sun Mar 25 14:20:43 2012	(r233465)
@@ -698,21 +698,25 @@ blkfront_initialize(struct xb_softc *sc)
 		return;
 
 	/* Support both backend schemes for relaying ring page limits. */
-	error = xs_printf(XST_NIL, node_path,
-			 "num-ring-pages","%u", sc->ring_pages);
-	if (error) {
-		xenbus_dev_fatal(sc->xb_dev, error,
-				 "writing %s/num-ring-pages",
-				 node_path);
-		return;
-	}
-	error = xs_printf(XST_NIL, node_path,
-			 "ring-page-order","%u", fls(sc->ring_pages) - 1);
-	if (error) {
-		xenbus_dev_fatal(sc->xb_dev, error,
-				 "writing %s/ring-page-order",
-				 node_path);
-		return;
+	if (sc->ring_pages > 1) {
+		error = xs_printf(XST_NIL, node_path,
+				 "num-ring-pages","%u", sc->ring_pages);
+		if (error) {
+			xenbus_dev_fatal(sc->xb_dev, error,
+					 "writing %s/num-ring-pages",
+					 node_path);
+			return;
+		}
+
+		error = xs_printf(XST_NIL, node_path,
+				 "ring-page-order", "%u",
+				 fls(sc->ring_pages) - 1);
+		if (error) {
+			xenbus_dev_fatal(sc->xb_dev, error,
+					 "writing %s/ring-page-order",
+					 node_path);
+			return;
+		}
 	}
 
 	error = xs_printf(XST_NIL, node_path,