NFSv4: Ensure change attribute returned by GETATTR callback conforms to spec

 According to RFC3530 we're supposed to cache the change attribute
 at the time the client receives a write delegation.
 If the inode is clean, a CB_GETATTR callback by the server to the
 client is supposed to return the cached change attribute.
 If, OTOH, the inode is dirty, the client should bump the cached
 change attribute by 1.

 Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>

fs/nfs/callback_proc.c

@@ -35,7 +35,9 @@ unsigned nfs4_callback_getattr(struct cb_getattrargs *args, struct cb_getattrres
 	if (delegation == NULL || (delegation->type & FMODE_WRITE) == 0)
 		goto out_iput;
 	res->size = i_size_read(inode);
-	res->change_attr = NFS_CHANGE_ATTR(inode);
+	res->change_attr = delegation->change_attr;
+	if (nfsi->npages != 0)
+		res->change_attr++;
 	res->ctime = inode->i_ctime;
 	res->mtime = inode->i_mtime;
 	res->bitmap[0] = (FATTR4_WORD0_CHANGE|FATTR4_WORD0_SIZE) &

fs/nfs/delegation.c

@@ -131,6 +131,7 @@ int nfs_inode_set_delegation(struct inode *inode, struct rpc_cred *cred, struct
 			sizeof(delegation->stateid.data));
 	delegation->type = res->delegation_type;
 	delegation->maxsize = res->maxsize;
+	delegation->change_attr = nfsi->change_attr;
 	delegation->cred = get_rpccred(cred);
 	delegation->inode = inode;
 

fs/nfs/delegation.h

@@ -21,6 +21,7 @@ struct nfs_delegation {
 #define NFS_DELEGATION_NEED_RECLAIM 1
 	long flags;
 	loff_t maxsize;
+	__u64 change_attr;
 };
 
 int nfs_inode_set_delegation(struct inode *inode, struct rpc_cred *cred, struct nfs_openres *res);