1 files changed, 21 insertions, 2 deletions

diff --git a/drivers/block/xen-blkback/xenbus.c b/drivers/block/xen-blkback/xenbus.c
index 4f66171c6683..b2250265308a 100644
--- a/drivers/block/xen-blkback/xenbus.c
+++ b/drivers/block/xen-blkback/xenbus.c
@@ -118,6 +118,7 @@ static struct xen_blkif *xen_blkif_alloc(domid_t domid)
         atomic_set(&blkif->drain, 0);
         blkif->st_print = jiffies;
         init_waitqueue_head(&blkif->waiting_to_free);
+        blkif->persistent_gnts.rb_node = NULL;
 
         return blkif;
 }
@@ -673,6 +674,13 @@ again:
 
         xen_blkbk_barrier(xbt, be, be->blkif->vbd.flush_support);
 
+        err = xenbus_printf(xbt, dev->nodename, "feature-persistent", "%u", 1);
+        if (err) {
+                xenbus_dev_fatal(dev, err, "writing %s/feature-persistent",
+                                 dev->nodename);
+                goto abort;
+        }
+
         err = xenbus_printf(xbt, dev->nodename, "sectors", "%llu",
                             (unsigned long long)vbd_sz(&be->blkif->vbd));
         if (err) {
@@ -721,6 +729,7 @@ static int connect_ring(struct backend_info *be)
         struct xenbus_device *dev = be->dev;
         unsigned long ring_ref;
         unsigned int evtchn;
+        unsigned int pers_grants;
         char protocol[64] = "";
         int err;
 
@@ -750,8 +759,18 @@ static int connect_ring(struct backend_info *be)
                 xenbus_dev_fatal(dev, err, "unknown fe protocol %s", protocol);
                 return -1;
         }
-        pr_info(DRV_PFX "ring-ref %ld, event-channel %d, protocol %d (%s)\n",
-                ring_ref, evtchn, be->blkif->blk_protocol, protocol);
+        err = xenbus_gather(XBT_NIL, dev->otherend,
+                            "feature-persistent-grants", "%u",
+                            &pers_grants, NULL);
+        if (err)
+                pers_grants = 0;
+
+        be->blkif->vbd.feature_gnt_persistent = pers_grants;
+        be->blkif->vbd.overflow_max_grants = 0;
+
+        pr_info(DRV_PFX "ring-ref %ld, event-channel %d, protocol %d (%s) %s\n",
+                ring_ref, evtchn, be->blkif->blk_protocol, protocol,
+                pers_grants ? "persistent grants" : "");
 
         /* Map the shared frame, irq etc. */
         err = xen_blkif_map(be->blkif, ring_ref, evtchn);