ovl: index directories on copy up for NFS export

With the NFS export feature enabled, all dirs are indexed on copy up.
Non-dir files are copied up directly to indexdir and then hardlinked
to upper dir.

Directories are copied up to indexdir, then an index entry is created
in indexdir with 'upper' xattr pointing to the copied up dir and then
the copied up dir is moved to upper dir.

Directory index is also used for consistency verification, like
detecting multiple redirected dirs to the same lower dir on lookup.
Signed-off-by: Amir Goldstein <amir73il@gmail.com>
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>

fs/overlayfs/copy_up.c

@@ -315,6 +315,94 @@ int ovl_set_origin(struct dentry *dentry, struct dentry *lower,
 	return err;
 }
 
+/* Store file handle of @upper dir in @index dir entry */
+static int ovl_set_upper_fh(struct dentry *upper, struct dentry *index)
+{
+	const struct ovl_fh *fh;
+	int err;
+
+	fh = ovl_encode_fh(upper, true);
+	if (IS_ERR(fh))
+		return PTR_ERR(fh);
+
+	err = ovl_do_setxattr(index, OVL_XATTR_UPPER, fh, fh->len, 0);
+
+	kfree(fh);
+	return err;
+}
+
+/*
+ * Create and install index entry.
+ *
+ * Caller must hold i_mutex on indexdir.
+ */
+static int ovl_create_index(struct dentry *dentry, struct dentry *origin,
+			    struct dentry *upper)
+{
+	struct dentry *indexdir = ovl_indexdir(dentry->d_sb);
+	struct inode *dir = d_inode(indexdir);
+	struct dentry *index = NULL;
+	struct dentry *temp = NULL;
+	struct qstr name = { };
+	int err;
+
+	/*
+	 * For now this is only used for creating index entry for directories,
+	 * because non-dir are copied up directly to index and then hardlinked
+	 * to upper dir.
+	 *
+	 * TODO: implement create index for non-dir, so we can call it when
+	 * encoding file handle for non-dir in case index does not exist.
+	 */
+	if (WARN_ON(!d_is_dir(dentry)))
+		return -EIO;
+
+	/* Directory not expected to be indexed before copy up */
+	if (WARN_ON(ovl_test_flag(OVL_INDEX, d_inode(dentry))))
+		return -EIO;
+
+	err = ovl_get_index_name(origin, &name);
+	if (err)
+		return err;
+
+	temp = ovl_lookup_temp(indexdir);
+	if (IS_ERR(temp))
+		goto temp_err;
+
+	err = ovl_do_mkdir(dir, temp, S_IFDIR, true);
+	if (err)
+		goto out;
+
+	err = ovl_set_upper_fh(upper, temp);
+	if (err)
+		goto out_cleanup;
+
+	index = lookup_one_len(name.name, indexdir, name.len);
+	if (IS_ERR(index)) {
+		err = PTR_ERR(index);
+	} else {
+		err = ovl_do_rename(dir, temp, dir, index, 0);
+		dput(index);
+	}
+
+	if (err)
+		goto out_cleanup;
+
+out:
+	dput(temp);
+	kfree(name.name);
+	return err;
+
+temp_err:
+	err = PTR_ERR(temp);
+	temp = NULL;
+	goto out;
+
+out_cleanup:
+	ovl_cleanup(dir, temp);
+	goto out;
+}
+
 struct ovl_copy_up_ctx {
 	struct dentry *parent;
 	struct dentry *dentry;
@@ -327,6 +415,7 @@ struct ovl_copy_up_ctx {
 	struct dentry *workdir;
 	bool tmpfile;
 	bool origin;
+	bool indexed;
 };
 
 static int ovl_link_up(struct ovl_copy_up_ctx *c)
@@ -498,6 +587,12 @@ static int ovl_copy_up_locked(struct ovl_copy_up_ctx *c)
 	if (err)
 		goto out_cleanup;
 
+	if (S_ISDIR(c->stat.mode) && c->indexed) {
+		err = ovl_create_index(c->dentry, c->lowerpath.dentry, temp);
+		if (err)
+			goto out_cleanup;
+	}
+
 	if (c->tmpfile) {
 		inode_lock_nested(udir, I_MUTEX_PARENT);
 		err = ovl_install_temp(c, temp, &newdentry);
@@ -536,12 +631,26 @@ static int ovl_do_copy_up(struct ovl_copy_up_ctx *c)
 {
 	int err;
 	struct ovl_fs *ofs = c->dentry->d_sb->s_fs_info;
-	bool indexed = ovl_need_index(c->dentry);
+	bool to_index = false;
+
+	/*
+	 * Indexed non-dir is copied up directly to the index entry and then
+	 * hardlinked to upper dir. Indexed dir is copied up to indexdir,
+	 * then index entry is created and then copied up dir installed.
+	 * Copying dir up to indexdir instead of workdir simplifies locking.
+	 */
+	if (ovl_need_index(c->dentry)) {
+		c->indexed = true;
+		if (S_ISDIR(c->stat.mode))
+			c->workdir = ovl_indexdir(c->dentry->d_sb);
+		else
+			to_index = true;
+	}
 
-	if (S_ISDIR(c->stat.mode) || c->stat.nlink == 1 || indexed)
+	if (S_ISDIR(c->stat.mode) || c->stat.nlink == 1 || to_index)
 		c->origin = true;
 
-	if (indexed) {
+	if (to_index) {
 		c->destdir = ovl_indexdir(c->dentry->d_sb);
 		err = ovl_get_index_name(c->lowerpath.dentry, &c->destname);
 		if (err)
@@ -568,9 +677,10 @@ static int ovl_do_copy_up(struct ovl_copy_up_ctx *c)
 		}
 	}
 
-	if (indexed) {
-		if (!err)
+	if (!err && c->indexed)
 		ovl_set_flag(OVL_INDEX, d_inode(c->dentry));
+
+	if (to_index) {
 		kfree(c->destname.name);
 	} else if (!err) {
 		struct inode *udir = d_inode(c->destdir);

fs/overlayfs/util.c

@@ -474,7 +474,7 @@ bool ovl_need_index(struct dentry *dentry)
 		return false;
 
 	/* Index all files for NFS export and consistency verification */
-	if (!d_is_dir(lower) && ovl_index_all(dentry->d_sb))
+	if (ovl_index_all(dentry->d_sb))
 		return true;
 
 	/* Index only lower hardlinks on copy up */