block/xen-blkfront: Store a page rather a pfn in the grant structure

All the usage of the field pfn are done using the same idiom:

pfn_to_page(grant->pfn)

This will  return always the same page. Store directly the page in the
grant to clean up the code.
Signed-off-by: Julien Grall <julien.grall@citrix.com>
Acked-by: Roger Pau Monné <roger.pau@citrix.com>
Reviewed-by: Stefano Stabellini <stefano.stabellini@eu.citrix.com>
Signed-off-by: David Vrabel <david.vrabel@citrix.com>

drivers/block/xen-blkfront.c

@@ -68,7 +68,7 @@ enum blkif_state {
 
 struct grant {
 	grant_ref_t gref;
-	unsigned long pfn;
+	struct page *page;
 	struct list_head node;
 };
 
@@ -221,7 +221,7 @@ static int fill_grant_buffer(struct blkfront_info *info, int num)
 				kfree(gnt_list_entry);
 				goto out_of_memory;
 			}
-			gnt_list_entry->pfn = page_to_pfn(granted_page);
+			gnt_list_entry->page = granted_page;
 		}
 
 		gnt_list_entry->gref = GRANT_INVALID_REF;
@@ -236,7 +236,7 @@ static int fill_grant_buffer(struct blkfront_info *info, int num)
 	                         &info->grants, node) {
 		list_del(&gnt_list_entry->node);
 		if (info->feature_persistent)
-			__free_page(pfn_to_page(gnt_list_entry->pfn));
+			__free_page(gnt_list_entry->page);
 		kfree(gnt_list_entry);
 		i--;
 	}
@@ -245,8 +245,8 @@ static int fill_grant_buffer(struct blkfront_info *info, int num)
 }
 
 static struct grant *get_grant(grant_ref_t *gref_head,
-                               unsigned long pfn,
-                               struct blkfront_info *info)
+			       struct page *page,
+			       struct blkfront_info *info)
 {
 	struct grant *gnt_list_entry;
 	unsigned long buffer_gfn;
@@ -265,10 +265,10 @@ static struct grant *get_grant(grant_ref_t *gref_head,
 	gnt_list_entry->gref = gnttab_claim_grant_reference(gref_head);
 	BUG_ON(gnt_list_entry->gref == -ENOSPC);
 	if (!info->feature_persistent) {
-		BUG_ON(!pfn);
-		gnt_list_entry->pfn = pfn;
+		BUG_ON(!page);
+		gnt_list_entry->page = page;
 	}
-	buffer_gfn = pfn_to_gfn(gnt_list_entry->pfn);
+	buffer_gfn = xen_page_to_gfn(gnt_list_entry->page);
 	gnttab_grant_foreign_access_ref(gnt_list_entry->gref,
 	                                info->xbdev->otherend_id,
 	                                buffer_gfn, 0);
@@ -524,7 +524,7 @@ static int blkif_queue_rw_req(struct request *req)
 
 		if ((ring_req->operation == BLKIF_OP_INDIRECT) &&
 		    (i % SEGS_PER_INDIRECT_FRAME == 0)) {
-			unsigned long uninitialized_var(pfn);
+			struct page *uninitialized_var(page);
 
 			if (segments)
 				kunmap_atomic(segments);
@@ -541,15 +541,15 @@ static int blkif_queue_rw_req(struct request *req)
 				indirect_page = list_first_entry(&info->indirect_pages,
 								 struct page, lru);
 				list_del(&indirect_page->lru);
-				pfn = page_to_pfn(indirect_page);
+				page = indirect_page;
 			}
-			gnt_list_entry = get_grant(&gref_head, pfn, info);
+			gnt_list_entry = get_grant(&gref_head, page, info);
 			info->shadow[id].indirect_grants[n] = gnt_list_entry;
-			segments = kmap_atomic(pfn_to_page(gnt_list_entry->pfn));
+			segments = kmap_atomic(gnt_list_entry->page);
 			ring_req->u.indirect.indirect_grefs[n] = gnt_list_entry->gref;
 		}
 
-		gnt_list_entry = get_grant(&gref_head, page_to_pfn(sg_page(sg)), info);
+		gnt_list_entry = get_grant(&gref_head, sg_page(sg), info);
 		ref = gnt_list_entry->gref;
 
 		info->shadow[id].grants_used[i] = gnt_list_entry;
@@ -560,7 +560,7 @@ static int blkif_queue_rw_req(struct request *req)
 
 			BUG_ON(sg->offset + sg->length > PAGE_SIZE);
 
-			shared_data = kmap_atomic(pfn_to_page(gnt_list_entry->pfn));
+			shared_data = kmap_atomic(gnt_list_entry->page);
 			bvec_data = kmap_atomic(sg_page(sg));
 
 			/*
@@ -1001,7 +1001,7 @@ static void blkif_free(struct blkfront_info *info, int suspend)
 				info->persistent_gnts_c--;
 			}
 			if (info->feature_persistent)
-				__free_page(pfn_to_page(persistent_gnt->pfn));
+				__free_page(persistent_gnt->page);
 			kfree(persistent_gnt);
 		}
 	}
@@ -1036,7 +1036,7 @@ static void blkif_free(struct blkfront_info *info, int suspend)
 			persistent_gnt = info->shadow[i].grants_used[j];
 			gnttab_end_foreign_access(persistent_gnt->gref, 0, 0UL);
 			if (info->feature_persistent)
-				__free_page(pfn_to_page(persistent_gnt->pfn));
+				__free_page(persistent_gnt->page);
 			kfree(persistent_gnt);
 		}
 
@@ -1050,7 +1050,7 @@ static void blkif_free(struct blkfront_info *info, int suspend)
 		for (j = 0; j < INDIRECT_GREFS(segs); j++) {
 			persistent_gnt = info->shadow[i].indirect_grants[j];
 			gnttab_end_foreign_access(persistent_gnt->gref, 0, 0UL);
-			__free_page(pfn_to_page(persistent_gnt->pfn));
+			__free_page(persistent_gnt->page);
 			kfree(persistent_gnt);
 		}
 
@@ -1101,8 +1101,7 @@ static void blkif_completion(struct blk_shadow *s, struct blkfront_info *info,
 	if (bret->operation == BLKIF_OP_READ && info->feature_persistent) {
 		for_each_sg(s->sg, sg, nseg, i) {
 			BUG_ON(sg->offset + sg->length > PAGE_SIZE);
-			shared_data = kmap_atomic(
-				pfn_to_page(s->grants_used[i]->pfn));
+			shared_data = kmap_atomic(s->grants_used[i]->page);
 			bvec_data = kmap_atomic(sg_page(sg));
 			memcpy(bvec_data   + sg->offset,
 			       shared_data + sg->offset,
@@ -1154,7 +1153,7 @@ static void blkif_completion(struct blk_shadow *s, struct blkfront_info *info,
 				 * available pages for indirect grefs.
 				 */
 				if (!info->feature_persistent) {
-					indirect_page = pfn_to_page(s->indirect_grants[i]->pfn);
+					indirect_page = s->indirect_grants[i]->page;
 					list_add(&indirect_page->lru, &info->indirect_pages);
 				}
 				s->indirect_grants[i]->gref = GRANT_INVALID_REF;