5 files changed, 63 insertions, 0 deletions

diff --git a/drivers/xen/xenbus/xenbus_comms.c b/drivers/xen/xenbus/xenbus_comms.c
index 2eff7a6aaa20..52fe7ad07666 100644
--- a/drivers/xen/xenbus/xenbus_comms.c
+++ b/drivers/xen/xenbus/xenbus_comms.c
@@ -234,3 +234,9 @@ int xb_init_comms(void)
 
         return 0;
 }
+
+void xb_deinit_comms(void)
+{
+        unbind_from_irqhandler(xenbus_irq, &xb_waitq);
+        xenbus_irq = 0;
+}
diff --git a/drivers/xen/xenbus/xenbus_comms.h b/drivers/xen/xenbus/xenbus_comms.h
index 6e42800fa499..c8abd3b8a6c4 100644
--- a/drivers/xen/xenbus/xenbus_comms.h
+++ b/drivers/xen/xenbus/xenbus_comms.h
@@ -35,6 +35,7 @@
 
 int xs_init(void);
 int xb_init_comms(void);
+void xb_deinit_comms(void);
 
 /* Low level routines. */
 int xb_write(const void *data, unsigned len);
diff --git a/drivers/xen/xenbus/xenbus_dev_backend.c b/drivers/xen/xenbus/xenbus_dev_backend.c
index 3d3be78c1093..be738c43104b 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 @@ static int xenbus_backend_open(struct inode *inode, struct file *filp)
         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 @@ static long xenbus_backend_ioctl(struct file *file, unsigned int cmd, unsigned l
                                 return xen_store_evtchn;
                         return -ENODEV;
 
+                case IOCTL_XENBUS_BACKEND_SETUP:
+                        return xenbus_alloc(data);
+
                 default:
                         return -ENOTTY;
         }
diff --git a/include/xen/grant_table.h b/include/xen/grant_table.h
index 15f8a00ff003..11e27c3af3cb 100644
--- a/include/xen/grant_table.h
+++ b/include/xen/grant_table.h
@@ -46,6 +46,8 @@
 
 #include <xen/features.h>
 
+#define GNTTAB_RESERVED_XENSTORE 1
+
 /* NR_GRANT_FRAMES must be less than or equal to that configured in Xen */
 #define NR_GRANT_FRAMES 4
 
diff --git a/include/xen/xenbus_dev.h b/include/xen/xenbus_dev.h
index ac5f0fe47ed9..bbee8c6a349d 100644
--- a/include/xen/xenbus_dev.h
+++ b/include/xen/xenbus_dev.h
@@ -38,4 +38,7 @@
 #define IOCTL_XENBUS_BACKEND_EVTCHN                     \
         _IOC(_IOC_NONE, 'B', 0, 0)
 
+#define IOCTL_XENBUS_BACKEND_SETUP                      \
+        _IOC(_IOC_NONE, 'B', 1, 0)
+
 #endif /* __LINUX_XEN_XENBUS_DEV_H__ */