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 <linux/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 */
nfs_superblock_set_dummy_root(struct super_block * sb,struct inode * inode)43 static 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 */
nfs_get_root(struct super_block * sb,struct nfs_fh * mntfh,const char * devname)71 struct 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);
129 out:
130 kfree(name);
131 nfs_free_fattr(fsinfo.fattr);
132 return ret;
133 }
134
