xref: /linux/fs/nfs/getroot.c (revision 827634added7f38b7d724cab1dccdb2b004c13c3)
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  */
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  */
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