x86: Unplug emulated disks and nics.

Add a xen_emul_unplug command line option to the kernel to unplug
xen emulated disks and nics.

Set the default value of xen_emul_unplug depending on whether or
not the Xen PV frontends and the Xen platform PCI driver have
been compiled for this kernel (modules or built-in are both OK).

The user can specify xen_emul_unplug=ignore to enable PV drivers on HVM
even if the host platform doesn't support unplug.

Signed-off-by: Stefano Stabellini <stefano.stabellini@eu.citrix.com>
Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>
diff --git a/drivers/block/xen-blkfront.c b/drivers/block/xen-blkfront.c
index 82ed403..6eb2989 100644
--- a/drivers/block/xen-blkfront.c
+++ b/drivers/block/xen-blkfront.c
@@ -48,6 +48,7 @@
 #include <xen/grant_table.h>
 #include <xen/events.h>
 #include <xen/page.h>
+#include <xen/platform_pci.h>
 
 #include <xen/interface/grant_table.h>
 #include <xen/interface/io/blkif.h>
@@ -737,6 +738,22 @@
 		}
 	}
 
+	/* no unplug has been done: do not hook devices != xen vbds */
+	if (xen_hvm_domain() && (xen_platform_pci_unplug & XEN_UNPLUG_IGNORE)) {
+		int major;
+
+		if (!VDEV_IS_EXTENDED(vdevice))
+			major = BLKIF_MAJOR(vdevice);
+		else
+			major = XENVBD_MAJOR;
+
+		if (major != XENVBD_MAJOR) {
+			printk(KERN_INFO
+					"%s: HVM does not support vbd %d as xen block device\n",
+					__FUNCTION__, vdevice);
+			return -ENODEV;
+		}
+	}
 	info = kzalloc(sizeof(*info), GFP_KERNEL);
 	if (!info) {
 		xenbus_dev_fatal(dev, -ENOMEM, "allocating info structure");