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 #define NFSDBG_FACILITY NFSDBG_CLIENT 36 37 /* 38 * Set the superblock root dentry. 39 * Note that this function frees the inode in case of error. 40 */ 41 static int nfs_superblock_set_dummy_root(struct super_block *sb, struct inode *inode) 42 { 43 /* The mntroot acts as the dummy root dentry for this superblock */ 44 if (sb->s_root == NULL) { 45 sb->s_root = d_make_root(inode); 46 if (sb->s_root == NULL) 47 return -ENOMEM; 48 ihold(inode); 49 /* 50 * Ensure that this dentry is invisible to d_find_alias(). 51 * Otherwise, it may be spliced into the tree by 52 * d_materialise_unique if a parent directory from the same 53 * filesystem gets mounted at a later time. 54 * This again causes shrink_dcache_for_umount_subtree() to 55 * Oops, since the test for IS_ROOT() will fail. 56 */ 57 spin_lock(&sb->s_root->d_inode->i_lock); 58 spin_lock(&sb->s_root->d_lock); 59 hlist_del_init(&sb->s_root->d_alias); 60 spin_unlock(&sb->s_root->d_lock); 61 spin_unlock(&sb->s_root->d_inode->i_lock); 62 } 63 return 0; 64 } 65 66 /* 67 * get an NFS2/NFS3 root dentry from the root filehandle 68 */ 69 struct dentry *nfs_get_root(struct super_block *sb, struct nfs_fh *mntfh, 70 const char *devname) 71 { 72 struct nfs_server *server = NFS_SB(sb); 73 struct nfs_fsinfo fsinfo; 74 struct dentry *ret; 75 struct inode *inode; 76 void *name = kstrdup(devname, GFP_KERNEL); 77 int error; 78 79 if (!name) 80 return ERR_PTR(-ENOMEM); 81 82 /* get the actual root for this mount */ 83 fsinfo.fattr = nfs_alloc_fattr(); 84 if (fsinfo.fattr == NULL) { 85 kfree(name); 86 return ERR_PTR(-ENOMEM); 87 } 88 89 error = server->nfs_client->rpc_ops->getroot(server, mntfh, &fsinfo); 90 if (error < 0) { 91 dprintk("nfs_get_root: getattr error = %d\n", -error); 92 ret = ERR_PTR(error); 93 goto out; 94 } 95 96 inode = nfs_fhget(sb, mntfh, fsinfo.fattr); 97 if (IS_ERR(inode)) { 98 dprintk("nfs_get_root: get root inode failed\n"); 99 ret = ERR_CAST(inode); 100 goto out; 101 } 102 103 error = nfs_superblock_set_dummy_root(sb, inode); 104 if (error != 0) { 105 ret = ERR_PTR(error); 106 goto out; 107 } 108 109 /* root dentries normally start off anonymous and get spliced in later 110 * if the dentry tree reaches them; however if the dentry already 111 * exists, we'll pick it up at this point and use it as the root 112 */ 113 ret = d_obtain_alias(inode); 114 if (IS_ERR(ret)) { 115 dprintk("nfs_get_root: get root dentry failed\n"); 116 goto out; 117 } 118 119 security_d_instantiate(ret, inode); 120 spin_lock(&ret->d_lock); 121 if (IS_ROOT(ret) && !(ret->d_flags & DCACHE_NFSFS_RENAMED)) { 122 ret->d_fsdata = name; 123 name = NULL; 124 } 125 spin_unlock(&ret->d_lock); 126 out: 127 if (name) 128 kfree(name); 129 nfs_free_fattr(fsinfo.fattr); 130 return ret; 131 } 132