v4.19.13 snapshot.
diff --git a/fs/nfs/getroot.c b/fs/nfs/getroot.c
new file mode 100644
index 0000000..391dafa
--- /dev/null
+++ b/fs/nfs/getroot.c
@@ -0,0 +1,133 @@
+/* getroot.c: get the root dentry for an NFS mount
+ *
+ * Copyright (C) 2006 Red Hat, Inc. All Rights Reserved.
+ * Written by David Howells (dhowells@redhat.com)
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License
+ * as published by the Free Software Foundation; either version
+ * 2 of the License, or (at your option) any later version.
+ */
+
+#include <linux/module.h>
+#include <linux/init.h>
+
+#include <linux/time.h>
+#include <linux/kernel.h>
+#include <linux/mm.h>
+#include <linux/string.h>
+#include <linux/stat.h>
+#include <linux/errno.h>
+#include <linux/unistd.h>
+#include <linux/sunrpc/clnt.h>
+#include <linux/sunrpc/stats.h>
+#include <linux/nfs_fs.h>
+#include <linux/nfs_mount.h>
+#include <linux/lockd/bind.h>
+#include <linux/seq_file.h>
+#include <linux/mount.h>
+#include <linux/vfs.h>
+#include <linux/namei.h>
+#include <linux/security.h>
+
+#include <linux/uaccess.h>
+
+#include "internal.h"
+
+#define NFSDBG_FACILITY NFSDBG_CLIENT
+
+/*
+ * Set the superblock root dentry.
+ * Note that this function frees the inode in case of error.
+ */
+static int nfs_superblock_set_dummy_root(struct super_block *sb, struct inode *inode)
+{
+ /* The mntroot acts as the dummy root dentry for this superblock */
+ if (sb->s_root == NULL) {
+ sb->s_root = d_make_root(inode);
+ if (sb->s_root == NULL)
+ return -ENOMEM;
+ ihold(inode);
+ /*
+ * Ensure that this dentry is invisible to d_find_alias().
+ * Otherwise, it may be spliced into the tree by
+ * d_splice_alias if a parent directory from the same
+ * filesystem gets mounted at a later time.
+ * This again causes shrink_dcache_for_umount_subtree() to
+ * Oops, since the test for IS_ROOT() will fail.
+ */
+ spin_lock(&d_inode(sb->s_root)->i_lock);
+ spin_lock(&sb->s_root->d_lock);
+ hlist_del_init(&sb->s_root->d_u.d_alias);
+ spin_unlock(&sb->s_root->d_lock);
+ spin_unlock(&d_inode(sb->s_root)->i_lock);
+ }
+ return 0;
+}
+
+/*
+ * get an NFS2/NFS3 root dentry from the root filehandle
+ */
+struct dentry *nfs_get_root(struct super_block *sb, struct nfs_fh *mntfh,
+ const char *devname)
+{
+ struct nfs_server *server = NFS_SB(sb);
+ struct nfs_fsinfo fsinfo;
+ struct dentry *ret;
+ struct inode *inode;
+ void *name = kstrdup(devname, GFP_KERNEL);
+ int error;
+
+ if (!name)
+ return ERR_PTR(-ENOMEM);
+
+ /* get the actual root for this mount */
+ fsinfo.fattr = nfs_alloc_fattr();
+ if (fsinfo.fattr == NULL) {
+ kfree(name);
+ return ERR_PTR(-ENOMEM);
+ }
+
+ error = server->nfs_client->rpc_ops->getroot(server, mntfh, &fsinfo);
+ if (error < 0) {
+ dprintk("nfs_get_root: getattr error = %d\n", -error);
+ ret = ERR_PTR(error);
+ goto out;
+ }
+
+ inode = nfs_fhget(sb, mntfh, fsinfo.fattr, NULL);
+ if (IS_ERR(inode)) {
+ dprintk("nfs_get_root: get root inode failed\n");
+ ret = ERR_CAST(inode);
+ goto out;
+ }
+
+ error = nfs_superblock_set_dummy_root(sb, inode);
+ if (error != 0) {
+ ret = ERR_PTR(error);
+ goto out;
+ }
+
+ /* root dentries normally start off anonymous and get spliced in later
+ * if the dentry tree reaches them; however if the dentry already
+ * exists, we'll pick it up at this point and use it as the root
+ */
+ ret = d_obtain_root(inode);
+ if (IS_ERR(ret)) {
+ dprintk("nfs_get_root: get root dentry failed\n");
+ goto out;
+ }
+
+ security_d_instantiate(ret, inode);
+ spin_lock(&ret->d_lock);
+ if (IS_ROOT(ret) && !ret->d_fsdata &&
+ !(ret->d_flags & DCACHE_NFSFS_RENAMED)) {
+ ret->d_fsdata = name;
+ name = NULL;
+ }
+ spin_unlock(&ret->d_lock);
+out:
+ kfree(name);
+ nfs_free_fattr(fsinfo.fattr);
+ return ret;
+}