NFS: Shortcut lookup revalidations if we have a directory delegation

Holding a directory delegation means we know that nobody else has
modified the directory on the server, so we can take a few revalidation
shortcuts.

Signed-off-by: Anna Schumaker <anna.schumaker@oracle.com>
Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>

Author: Anna Schumaker

fs/nfs/delegation.h

@@ -130,6 +130,11 @@ static inline void nfs_request_directory_delegation(struct inode *inode)
 		set_bit(NFS_INO_REQ_DIR_DELEG, &NFS_I(inode)->flags);
 }
 
+static inline bool nfs_have_directory_delegation(struct inode *inode)
+{
+	return S_ISDIR(inode->i_mode) && nfs_have_delegated_attributes(inode);
+}
+
 int nfs4_delegation_hash_alloc(struct nfs_server *server);
 
 #endif

fs/nfs/dir.c

@@ -1515,6 +1515,15 @@ static int nfs_check_verifier(struct inode *dir, struct dentry *dentry,
 		return 0;
 	if (!nfs_dentry_verify_change(dir, dentry))
 		return 0;
+
+	/*
+	 * If we have a directory delegation then we don't need to revalidate
+	 * the directory. The delegation will either get recalled or we will
+	 * receive a notification when it changes.
+	 */
+	if (nfs_have_directory_delegation(dir))
+		return 0;
+
 	/* Revalidate nfsi->cache_change_attribute before we declare a match */
 	if (nfs_mapping_need_revalidate_inode(dir)) {
 		if (rcu_walk)
@@ -2207,6 +2216,13 @@ int nfs_atomic_open(struct inode *dir, struct dentry *dentry,
 }
 EXPORT_SYMBOL_GPL(nfs_atomic_open);
 
+static int
+nfs_lookup_revalidate_delegated_parent(struct inode *dir, struct dentry *dentry,
+				       struct inode *inode)
+{
+	return nfs_lookup_revalidate_done(dir, dentry, inode, 1);
+}
+
 static int
 nfs4_lookup_revalidate(struct inode *dir, const struct qstr *name,
 		       struct dentry *dentry, unsigned int flags)
@@ -2234,6 +2250,9 @@ nfs4_lookup_revalidate(struct inode *dir, const struct qstr *name,
 	if (nfs_verifier_is_delegated(dentry))
 		return nfs_lookup_revalidate_delegated(dir, dentry, inode);
 
+	if (nfs_have_directory_delegation(dir))
+		return nfs_lookup_revalidate_delegated_parent(dir, dentry, inode);
+
 	/* NFS only supports OPEN on regular files */
 	if (!S_ISREG(inode->i_mode))
 		goto full_reval;

fs/nfs/inode.c

@@ -1389,6 +1389,9 @@ __nfs_revalidate_inode(struct nfs_server *server, struct inode *inode)
 		status = pnfs_sync_inode(inode, false);
 		if (status)
 			goto out;
+	} else if (nfs_have_directory_delegation(inode)) {
+		status = 0;
+		goto out;
 	}
 
 	status = -ENOMEM;