svn commit: r256423 - head/sys/dev/xen/blkfront

[Justin T. Gibbs]

Author: gibbs
Date: Sun Oct 13 02:34:20 2013
New Revision: 256423
URL: http://svnweb.freebsd.org/changeset/base/256423

Log:
  Allow FreeBSD to be booted from CDROM media on XenServer 6.2 and
  prior releases.
  
  Submitted by:	Roger Pau Monné
  Sponsored by:	Citrix Systems R&D
  Reviewed by:	gibbs
  Approved by:	re (gjb)
  
  sys/dev/xen/blkfront/blkfront.c:
  	On XenServer versions up to an including 6.2, paravirtualized
  	CDROM support is broken.  When running in an HVM domain,
  	ignore paravirtualized instances of CDROM media, and instead
  	rely on native drivers attaching to emulated hardware.  This
  	functions correctly on all currently known Xen based
  	platforms.

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

Modified: head/sys/dev/xen/blkfront/blkfront.c
==============================================================================
--- head/sys/dev/xen/blkfront/blkfront.c	Sun Oct 13 00:29:14 2013	(r256422)
+++ head/sys/dev/xen/blkfront/blkfront.c	Sun Oct 13 02:34:20 2013	(r256423)
@@ -1381,14 +1381,42 @@ xbd_closing(device_t dev)
 static int
 xbd_probe(device_t dev)
 {
+	if (strcmp(xenbus_get_type(dev), "vbd") != 0)
+		return (ENXIO);
 
-	if (!strcmp(xenbus_get_type(dev), "vbd")) {
-		device_set_desc(dev, "Virtual Block Device");
-		device_quiet(dev);
-		return (0);
+	if (xen_hvm_domain()) {
+		int error;
+		char *type;
+
+		/*
+		 * When running in an HVM domain, IDE disk emulation is
+		 * disabled early in boot so that native drivers will
+		 * not see emulated hardware.  However, CDROM device
+		 * emulation cannot be disabled.
+		 *
+		 * Through use of FreeBSD's vm_guest and xen_hvm_domain()
+		 * APIs, we could modify the native CDROM driver to fail its
+		 * probe when running under Xen.  Unfortunatlely, the PV
+		 * CDROM support in XenServer (up through at least version
+		 * 6.2) isn't functional, so we instead rely on the emulated
+		 * CDROM instance, and fail to attach the PV one here in
+		 * the blkfront driver.
+		 */
+		error = xs_read(XST_NIL, xenbus_get_node(dev),
+		    "device-type", NULL, (void **) &type);
+		if (error)
+			return (ENXIO);
+
+		if (strncmp(type, "cdrom", 5) == 0) {
+			free(type, M_XENSTORE);
+			return (ENXIO);
+		}
+		free(type, M_XENSTORE);
 	}
 
-	return (ENXIO);
+	device_set_desc(dev, "Virtual Block Device");
+	device_quiet(dev);
+	return (0);
 }
 
 /*