/* 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 <asm/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_materialise_unique 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(&sb->s_root->d_inode->i_lock);
  		spin_lock(&sb->s_root->d_lock);
  		hlist_del_init(&sb->s_root->d_alias);
  		spin_unlock(&sb->s_root->d_lock);
  		spin_unlock(&sb->s_root->d_inode->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
  ", -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
  ");
  		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_alias(inode);
  	if (IS_ERR(ret)) {
  		dprintk("nfs_get_root: get root dentry failed
  ");
  		goto out;
  	}
  
  	security_d_instantiate(ret, inode);
  	spin_lock(&ret->d_lock);
  	if (IS_ROOT(ret) && !(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;
  }