1/* getroot.c: get the root dentry for an NFS mount
2 *
3 * Copyright (C) 2006 Red Hat, Inc. All Rights Reserved.
4 * Written by David Howells (dhowells@redhat.com)
5 *
6 * This program is free software; you can redistribute it and/or
7 * modify it under the terms of the GNU General Public License
8 * as published by the Free Software Foundation; either version
9 * 2 of the License, or (at your option) any later version.
10 */
11
12#include <linux/module.h>
13#include <linux/init.h>
14
15#include <linux/time.h>
16#include <linux/kernel.h>
17#include <linux/mm.h>
18#include <linux/string.h>
19#include <linux/stat.h>
20#include <linux/errno.h>
21#include <linux/unistd.h>
22#include <linux/sunrpc/clnt.h>
23#include <linux/sunrpc/stats.h>
24#include <linux/nfs_fs.h>
25#include <linux/nfs_mount.h>
26#include <linux/lockd/bind.h>
27#include <linux/seq_file.h>
28#include <linux/mount.h>
29#include <linux/vfs.h>
30#include <linux/namei.h>
31#include <linux/security.h>
32
33#include <asm/uaccess.h>
34
35#include "internal.h"
36
37#define NFSDBG_FACILITY		NFSDBG_CLIENT
38
39/*
40 * Set the superblock root dentry.
41 * Note that this function frees the inode in case of error.
42 */
43static int nfs_superblock_set_dummy_root(struct super_block *sb, struct inode *inode)
44{
45	/* The mntroot acts as the dummy root dentry for this superblock */
46	if (sb->s_root == NULL) {
47		sb->s_root = d_make_root(inode);
48		if (sb->s_root == NULL)
49			return -ENOMEM;
50		ihold(inode);
51		/*
52		 * Ensure that this dentry is invisible to d_find_alias().
53		 * Otherwise, it may be spliced into the tree by
54		 * d_splice_alias if a parent directory from the same
55		 * filesystem gets mounted at a later time.
56		 * This again causes shrink_dcache_for_umount_subtree() to
57		 * Oops, since the test for IS_ROOT() will fail.
58		 */
59		spin_lock(&d_inode(sb->s_root)->i_lock);
60		spin_lock(&sb->s_root->d_lock);
61		hlist_del_init(&sb->s_root->d_u.d_alias);
62		spin_unlock(&sb->s_root->d_lock);
63		spin_unlock(&d_inode(sb->s_root)->i_lock);
64	}
65	return 0;
66}
67
68/*
69 * get an NFS2/NFS3 root dentry from the root filehandle
70 */
71struct dentry *nfs_get_root(struct super_block *sb, struct nfs_fh *mntfh,
72			    const char *devname)
73{
74	struct nfs_server *server = NFS_SB(sb);
75	struct nfs_fsinfo fsinfo;
76	struct dentry *ret;
77	struct inode *inode;
78	void *name = kstrdup(devname, GFP_KERNEL);
79	int error;
80
81	if (!name)
82		return ERR_PTR(-ENOMEM);
83
84	/* get the actual root for this mount */
85	fsinfo.fattr = nfs_alloc_fattr();
86	if (fsinfo.fattr == NULL) {
87		kfree(name);
88		return ERR_PTR(-ENOMEM);
89	}
90
91	error = server->nfs_client->rpc_ops->getroot(server, mntfh, &fsinfo);
92	if (error < 0) {
93		dprintk("nfs_get_root: getattr error = %d\n", -error);
94		ret = ERR_PTR(error);
95		goto out;
96	}
97
98	inode = nfs_fhget(sb, mntfh, fsinfo.fattr, NULL);
99	if (IS_ERR(inode)) {
100		dprintk("nfs_get_root: get root inode failed\n");
101		ret = ERR_CAST(inode);
102		goto out;
103	}
104
105	error = nfs_superblock_set_dummy_root(sb, inode);
106	if (error != 0) {
107		ret = ERR_PTR(error);
108		goto out;
109	}
110
111	/* root dentries normally start off anonymous and get spliced in later
112	 * if the dentry tree reaches them; however if the dentry already
113	 * exists, we'll pick it up at this point and use it as the root
114	 */
115	ret = d_obtain_root(inode);
116	if (IS_ERR(ret)) {
117		dprintk("nfs_get_root: get root dentry failed\n");
118		goto out;
119	}
120
121	security_d_instantiate(ret, inode);
122	spin_lock(&ret->d_lock);
123	if (IS_ROOT(ret) && !ret->d_fsdata &&
124	    !(ret->d_flags & DCACHE_NFSFS_RENAMED)) {
125		ret->d_fsdata = name;
126		name = NULL;
127	}
128	spin_unlock(&ret->d_lock);
129out:
130	kfree(name);
131	nfs_free_fattr(fsinfo.fattr);
132	return ret;
133}
134