xen/blkback: persistent-grants fixes

This patch contains fixes for persistent grants implementation v2:

 * handle == 0 is a valid handle, so initialize grants in blkback
   setting the handle to BLKBACK_INVALID_HANDLE instead of 0. Reported
   by Konrad Rzeszutek Wilk.

 * new_map is a boolean, use "true" or "false" instead of 1 and 0.
   Reported by Konrad Rzeszutek Wilk.

 * blkfront announces the persistent-grants feature as
   feature-persistent-grants, use feature-persistent instead which is
   consistent with blkback and the public Xen headers.

 * Add a consistency check in blkfront to make sure we don't try to
   access segments that have not been set.

Reported-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Signed-off-by: Roger Pau Monne <roger.pau@citrix.com>
[v1: The new_map int->bool had already been changed]
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>

drivers/block/xen-blkback/blkback.c

@@ -512,7 +512,7 @@ static int xen_blkbk_map(struct blkif_request *req,
 			 * not mapped but we have room for it
 			 */
 			new_map = true;
-			persistent_gnt = kzalloc(
+			persistent_gnt = kmalloc(
 				sizeof(struct persistent_gnt),
 				GFP_KERNEL);
 			if (!persistent_gnt)
@@ -523,6 +523,7 @@ static int xen_blkbk_map(struct blkif_request *req,
 				return -ENOMEM;
 			}
 			persistent_gnt->gnt = req->u.rw.seg[i].gref;
+			persistent_gnt->handle = BLKBACK_INVALID_HANDLE;
 
 			pages_to_gnt[segs_to_map] =
 				persistent_gnt->page;
@@ -584,7 +585,8 @@ static int xen_blkbk_map(struct blkif_request *req,
 	 */
 	bitmap_zero(pending_req->unmap_seg, BLKIF_MAX_SEGMENTS_PER_REQUEST);
 	for (i = 0, j = 0; i < nseg; i++) {
-		if (!persistent_gnts[i] || !persistent_gnts[i]->handle) {
+		if (!persistent_gnts[i] ||
+		    persistent_gnts[i]->handle == BLKBACK_INVALID_HANDLE) {
 			/* This is a newly mapped grant */
 			BUG_ON(j >= segs_to_map);
 			if (unlikely(map[j].status != 0)) {
@@ -601,7 +603,8 @@ static int xen_blkbk_map(struct blkif_request *req,
 			}
 		}
 		if (persistent_gnts[i]) {
-			if (!persistent_gnts[i]->handle) {
+			if (persistent_gnts[i]->handle ==
+			    BLKBACK_INVALID_HANDLE) {
 				/*
 				 * If this is a new persistent grant
 				 * save the handler

drivers/block/xen-blkback/xenbus.c

@@ -760,7 +760,7 @@ static int connect_ring(struct backend_info *be)
 		return -1;
 	}
 	err = xenbus_gather(XBT_NIL, dev->otherend,
-			    "feature-persistent-grants", "%u",
+			    "feature-persistent", "%u",
 			    &pers_grants, NULL);
 	if (err)
 		pers_grants = 0;

drivers/block/xen-blkfront.c

@@ -852,6 +852,7 @@ static void blkif_completion(struct blk_shadow *s, struct blkfront_info *info,
 		rq_for_each_segment(bvec, s->request, iter) {
 			BUG_ON((bvec->bv_offset + bvec->bv_len) > PAGE_SIZE);
 			i = offset >> PAGE_SHIFT;
+			BUG_ON(i >= s->req.u.rw.nr_segments);
 			shared_data = kmap_atomic(
 				pfn_to_page(s->grants_used[i]->pfn));
 			bvec_data = bvec_kmap_irq(bvec, &flags);
@@ -1069,7 +1070,7 @@ static int talk_to_blkback(struct xenbus_device *dev,
 		goto abort_transaction;
 	}
 	err = xenbus_printf(xbt, dev->nodename,
-			    "feature-persistent-grants", "%u", 1);
+			    "feature-persistent", "%u", 1);
 	if (err)
 		dev_warn(&dev->dev,
 			 "writing persistent grants feature to xenbus");