NFS: Don't fail an O_DIRECT read/write if get_user_pages() returns pages

There is no need to fail the entire O_DIRECT read/write just because
get_user_pages() returned fewer pages than we requested.
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>

fs/nfs/direct.c

@@ -295,10 +295,15 @@ static ssize_t nfs_direct_read_schedule(struct nfs_direct_req *dreq, unsigned lo
 			break;
 		}
 		if ((unsigned)result < data->npages) {
+			bytes = result * PAGE_SIZE;
+			if (bytes <= pgbase) {
 				nfs_direct_release_pages(data->pagevec, result);
 				nfs_readdata_release(data);
 				break;
 			}
+			bytes -= pgbase;
+			data->npages = result;
+		}
 
 		get_dreq(dreq);
 
@@ -630,10 +635,15 @@ static ssize_t nfs_direct_write_schedule(struct nfs_direct_req *dreq, unsigned l
 			break;
 		}
 		if ((unsigned)result < data->npages) {
+			bytes = result * PAGE_SIZE;
+			if (bytes <= pgbase) {
 				nfs_direct_release_pages(data->pagevec, result);
 				nfs_writedata_release(data);
 				break;
 			}
+			bytes -= pgbase;
+			data->npages = result;
+		}
 
 		get_dreq(dreq);