[PATCH] Support for cached lookups via readdirplus [4/6]

Add support for positive lookups using the READDIRPLUS cached
information. Both new lookups and lookup revalidation is supported.

Use READDIRPLUS instead of READDIR on NFSv3 directories with lengths
shorter than 8*PAGE_SIZE.

Note that inode attribute information is only updated if it is seen to
be more recent than any existing cached information.

fs/nfs/dir.c

@@ -37,6 +37,8 @@
 
 static int nfs_readdir(struct file *, void *, filldir_t);
 static struct dentry *nfs_lookup(struct inode *, struct dentry *);
+static int nfs_cached_lookup(struct inode *, struct dentry *,
+				struct nfs_fh *, struct nfs_fattr *);
 static int nfs_create(struct inode *, struct dentry *, int);
 static int nfs_mkdir(struct inode *, struct dentry *, int);
 static int nfs_rmdir(struct inode *, struct dentry *);
@@ -504,6 +506,15 @@ static int nfs_lookup_revalidate(struct dentry * dentry, int flags)
 		goto out_valid;
 	}
 
+	error = nfs_cached_lookup(dir, dentry, &fhandle, &fattr);
+	if (!error) {
+		if (memcmp(NFS_FH(inode), &fhandle, sizeof(struct nfs_fh))!= 0)
+			goto out_bad;
+		if (nfs_lookup_verify_inode(inode))
+			goto out_bad;
+		goto out_valid_renew;
+	}
+
 	if (NFS_STALE(inode))
 		goto out_bad;
 
@@ -515,6 +526,7 @@ static int nfs_lookup_revalidate(struct dentry * dentry, int flags)
 	if ((error = nfs_refresh_inode(inode, &fattr)) != 0)
 		goto out_bad;
 
+ out_valid_renew:
 	nfs_renew_times(dentry);
  out_valid:
 	unlock_kernel();
@@ -578,7 +590,7 @@ struct dentry_operations nfs_dentry_operations = {
 
 static struct dentry *nfs_lookup(struct inode *dir, struct dentry * dentry)
 {
-	struct inode *inode;
+	struct inode *inode = NULL;
 	int error;
 	struct nfs_fh fhandle;
 	struct nfs_fattr fattr;
@@ -594,8 +606,19 @@ static struct dentry *nfs_lookup(struct inode *dir, struct dentry * dentry)
 	dentry->d_op = &nfs_dentry_operations;
 
 	lock_kernel();
+	error = nfs_cached_lookup(dir, dentry, &fhandle, &fattr);
+	if (!error) {
+		error = -EACCES;
+		inode = nfs_fhget(dentry, &fhandle, &fattr);
+		if (inode) {
+			d_add(dentry, inode);
+			nfs_renew_times(dentry);
+			error = 0;
+		}
+		goto out;
+	}
+
 	error = NFS_PROTO(dir)->lookup(dir, &dentry->d_name, &fhandle, &fattr);
-	inode = NULL;
 	if (error == -ENOENT)
 		goto no_entry;
 	if (!error) {
@@ -613,6 +636,79 @@ static struct dentry *nfs_lookup(struct inode *dir, struct dentry * dentry)
 	return ERR_PTR(error);
 }
 
+static inline
+int find_dirent_name(nfs_readdir_descriptor_t *desc, struct page *page, struct dentry *dentry)
+{
+	struct nfs_entry *entry = desc->entry;
+	int		 status;
+
+	while((status = dir_decode(desc)) == 0) {
+		if (entry->len != dentry->d_name.len)
+			continue;
+		if (memcmp(entry->name, dentry->d_name.name, entry->len))
+			continue;
+		if (!(entry->fattr->valid & NFS_ATTR_FATTR))
+			continue;
+		break;
+	}
+	return status;
+}
+
+/*
+ * Use the cached Readdirplus results in order to avoid a LOOKUP call
+ * whenever we believe that the parent directory has not changed.
+ *
+ * We assume that any file creation/rename changes the directory mtime.
+ * As this results in a page cache invalidation whenever it occurs,
+ * we don't require any other tests for cache coherency.
+ */
+static
+int nfs_cached_lookup(struct inode *dir, struct dentry *dentry,
+			struct nfs_fh *fh, struct nfs_fattr *fattr)
+{
+	nfs_readdir_descriptor_t desc;
+	struct nfs_server *server;
+	struct nfs_entry entry;
+	struct page *page;
+	unsigned long timestamp = NFS_MTIME_UPDATE(dir);
+	int res;
+
+	if (!NFS_USE_READDIRPLUS(dir))
+		return -ENOENT;
+	server = NFS_SERVER(dir);
+	if (server->flags & NFS_MOUNT_NOAC)
+		return -ENOENT;
+	nfs_revalidate_inode(server, dir);
+
+	entry.fh = fh;
+	entry.fattr = fattr;
+
+	desc.decode = NFS_PROTO(dir)->decode_dirent;
+	desc.entry = &entry;
+	desc.page_index = 0;
+	desc.plus = 1;
+
+	for(;(page = find_get_page(&dir->i_data, desc.page_index)); desc.page_index++) {
+
+		res = -EIO;
+		if (PageUptodate(page)) {
+			desc.ptr = kmap(page);
+			res = find_dirent_name(&desc, page, dentry);
+			kunmap(page);
+		}
+		page_cache_release(page);
+
+		if (res == 0)
+			goto out_found;
+		if (res != -EAGAIN)
+			break;
+	}
+	return -ENOENT;
+ out_found:
+	fattr->timestamp = timestamp;
+	return 0;
+}
+
 /*
  * Code common to create, mkdir, and mknod.
  */

fs/nfs/inode.c

@@ -644,6 +644,9 @@ nfs_fhget(struct dentry *dentry, struct nfs_fh *fhandle,
 	return __nfs_fhget(sb, fhandle, fattr);
 }
 
+/* Don't use READDIRPLUS on directories that we believe are too large */
+#define NFS_LIMIT_READDIRPLUS (8*PAGE_SIZE)
+
 /*
  * Look up the inode by super block and fattr->fileid.
  */
@@ -692,6 +695,9 @@ __nfs_fhget(struct super_block *sb, struct nfs_fh *fh, struct nfs_fattr *fattr)
 		} else if (S_ISDIR(inode->i_mode)) {
 			inode->i_op = &nfs_dir_inode_operations;
 			inode->i_fop = &nfs_dir_operations;
+			if (nfs_server_capable(inode, NFS_CAP_READDIRPLUS)
+			    && fattr->size <= NFS_LIMIT_READDIRPLUS)
+				NFS_FLAGS(inode) |= NFS_INO_ADVISE_RDPLUS;
 		} else if (S_ISLNK(inode->i_mode))
 			inode->i_op = &nfs_symlink_inode_operations;
 		else