linux/fs/nfs/getroot.c
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   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 */
  41static 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 */
  69struct 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);
 126out:
 127        if (name)
 128                kfree(name);
 129        nfs_free_fattr(fsinfo.fattr);
 130        return ret;
 131}
 132
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