xenbus: Add support for xenbus backend in stub domain
Add an ioctl to the /dev/xen/xenbus_backend device allowing the xenbus
backend to be started after the kernel has booted. This allows xenstore
to run in a different domain from the dom0.
Signed-off-by: Daniel De Graaf <dgdegra@tycho.nsa.gov>
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
diff --git a/drivers/xen/xenbus/xenbus_dev_backend.c b/drivers/xen/xenbus/xenbus_dev_backend.c
index 3d3be78..be738c4 100644
--- a/drivers/xen/xenbus/xenbus_dev_backend.c
+++ b/drivers/xen/xenbus/xenbus_dev_backend.c
@@ -8,7 +8,11 @@
#include <xen/xen.h>
#include <xen/page.h>
+#include <xen/xenbus.h>
#include <xen/xenbus_dev.h>
+#include <xen/grant_table.h>
+#include <xen/events.h>
+#include <asm/xen/hypervisor.h>
#include "xenbus_comms.h"
@@ -22,6 +26,50 @@
return nonseekable_open(inode, filp);
}
+static long xenbus_alloc(domid_t domid)
+{
+ struct evtchn_alloc_unbound arg;
+ int err = -EEXIST;
+
+ xs_suspend();
+
+ /* If xenstored_ready is nonzero, that means we have already talked to
+ * xenstore and set up watches. These watches will be restored by
+ * xs_resume, but that requires communication over the port established
+ * below that is not visible to anyone until the ioctl returns.
+ *
+ * This can be resolved by splitting the ioctl into two parts
+ * (postponing the resume until xenstored is active) but this is
+ * unnecessarily complex for the intended use where xenstored is only
+ * started once - so return -EEXIST if it's already running.
+ */
+ if (xenstored_ready)
+ goto out_err;
+
+ gnttab_grant_foreign_access_ref(GNTTAB_RESERVED_XENSTORE, domid,
+ virt_to_mfn(xen_store_interface), 0 /* writable */);
+
+ arg.dom = DOMID_SELF;
+ arg.remote_dom = domid;
+
+ err = HYPERVISOR_event_channel_op(EVTCHNOP_alloc_unbound, &arg);
+ if (err)
+ goto out_err;
+
+ if (xen_store_evtchn > 0)
+ xb_deinit_comms();
+
+ xen_store_evtchn = arg.port;
+
+ xs_resume();
+
+ return arg.port;
+
+ out_err:
+ xs_suspend_cancel();
+ return err;
+}
+
static long xenbus_backend_ioctl(struct file *file, unsigned int cmd, unsigned long data)
{
if (!capable(CAP_SYS_ADMIN))
@@ -33,6 +81,9 @@
return xen_store_evtchn;
return -ENODEV;
+ case IOCTL_XENBUS_BACKEND_SETUP:
+ return xenbus_alloc(data);
+
default:
return -ENOTTY;
}