NFS: Fake up 'wcc' attributes to prevent cache invalidation after write

NFSv2 and v4 don't offer weak cache consistency attributes on WRITE calls.
In NFSv3, returning wcc data is optional. In all cases, we want to prevent
the client from invalidating our cached data whenever ->write_done()
attempts to update the inode attributes.
Signed-off-by: NTrond Myklebust <Trond.Myklebust@netapp.com>

fs/nfs/inode.c

@@ -793,6 +793,12 @@ static void nfs_wcc_update_inode(struct inode *inode, struct nfs_fattr *fattr)
 {
 	struct nfs_inode *nfsi = NFS_I(inode);
 
+	if ((fattr->valid & NFS_ATTR_WCC_V4) != 0 &&
+			nfsi->change_attr == fattr->pre_change_attr) {
+		nfsi->change_attr = fattr->change_attr;
+		if (S_ISDIR(inode->i_mode))
+			nfsi->cache_validity |= NFS_INO_INVALID_DATA;
+	}
 	/* If we have atomic WCC data, we may update some attributes */
 	if ((fattr->valid & NFS_ATTR_WCC) != 0) {
 		if (timespec_equal(&inode->i_ctime, &fattr->pre_ctime))
@@ -923,6 +929,34 @@ int nfs_post_op_update_inode(struct inode *inode, struct nfs_fattr *fattr)
 	return status;
 }
 
+/**
+ * nfs_post_op_update_inode_force_wcc - try to update the inode attribute cache
+ * @inode - pointer to inode
+ * @fattr - updated attributes
+ *
+ * After an operation that has changed the inode metadata, mark the
+ * attribute cache as being invalid, then try to update it. Fake up
+ * weak cache consistency data, if none exist.
+ *
+ * This function is mainly designed to be used by the ->write_done() functions.
+ */
+int nfs_post_op_update_inode_force_wcc(struct inode *inode, struct nfs_fattr *fattr)
+{
+	if ((fattr->valid & NFS_ATTR_FATTR_V4) != 0 &&
+			(fattr->valid & NFS_ATTR_WCC_V4) == 0) {
+		fattr->pre_change_attr = NFS_I(inode)->change_attr;
+		fattr->valid |= NFS_ATTR_WCC_V4;
+	}
+	if ((fattr->valid & NFS_ATTR_FATTR) != 0 &&
+			(fattr->valid & NFS_ATTR_WCC) == 0) {
+		memcpy(&fattr->pre_ctime, &inode->i_ctime, sizeof(fattr->pre_ctime));
+		memcpy(&fattr->pre_mtime, &inode->i_mtime, sizeof(fattr->pre_mtime));
+		fattr->pre_size = inode->i_size;
+		fattr->valid |= NFS_ATTR_WCC;
+	}
+	return nfs_post_op_update_inode(inode, fattr);
+}
+
 /*
  * Many nfs protocol calls return the new file attributes after
  * an operation.  Here we update the inode to reflect the state

fs/nfs/nfs3proc.c

@@ -750,7 +750,7 @@ static int nfs3_write_done(struct rpc_task *task, struct nfs_write_data *data)
 	if (nfs3_async_handle_jukebox(task, data->inode))
 		return -EAGAIN;
 	if (task->tk_status >= 0)
-		nfs_post_op_update_inode(data->inode, data->res.fattr);
+		nfs_post_op_update_inode_force_wcc(data->inode, data->res.fattr);
 	return 0;
 }
 

fs/nfs/nfs4proc.c

@@ -2427,7 +2427,7 @@ static int nfs4_write_done(struct rpc_task *task, struct nfs_write_data *data)
 	}
 	if (task->tk_status >= 0) {
 		renew_lease(NFS_SERVER(inode), data->timestamp);
-		nfs_post_op_update_inode(inode, data->res.fattr);
+		nfs_post_op_update_inode_force_wcc(inode, data->res.fattr);
 	}
 	return 0;
 }

fs/nfs/proc.c

@@ -579,7 +579,7 @@ static void nfs_proc_read_setup(struct nfs_read_data *data)
 static int nfs_write_done(struct rpc_task *task, struct nfs_write_data *data)
 {
 	if (task->tk_status >= 0)
-		nfs_post_op_update_inode(data->inode, data->res.fattr);
+		nfs_post_op_update_inode_force_wcc(data->inode, data->res.fattr);
 	return 0;
 }
 

include/linux/nfs_fs.h

@@ -293,6 +293,7 @@ extern struct inode *nfs_fhget(struct super_block *, struct nfs_fh *,
 				struct nfs_fattr *);
 extern int nfs_refresh_inode(struct inode *, struct nfs_fattr *);
 extern int nfs_post_op_update_inode(struct inode *inode, struct nfs_fattr *fattr);
+extern int nfs_post_op_update_inode_force_wcc(struct inode *inode, struct nfs_fattr *fattr);
 extern int nfs_getattr(struct vfsmount *, struct dentry *, struct kstat *);
 extern int nfs_permission(struct inode *, int, struct nameidata *);
 extern int nfs_open(struct inode *, struct file *);

include/linux/nfs_xdr.h

@@ -62,7 +62,8 @@ struct nfs_fattr {
 #define NFS_ATTR_FATTR		0x0002		/* post-op attributes */
 #define NFS_ATTR_FATTR_V3	0x0004		/* NFSv3 attributes */
 #define NFS_ATTR_FATTR_V4	0x0008		/* NFSv4 change attribute */
-#define NFS_ATTR_FATTR_V4_REFERRAL	0x0010		/* NFSv4 referral */
+#define NFS_ATTR_WCC_V4		0x0010		/* pre-op change attribute */
+#define NFS_ATTR_FATTR_V4_REFERRAL	0x0020		/* NFSv4 referral */
 
 /*
  * Info on the file system