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 */ 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