LXR linux/fs/nfs/getroot.c

   1// SPDX-License-Identifier: GPL-2.0-or-later
   2/* getroot.c: get the root dentry for an NFS mount
   3 *
   4 * Copyright (C) 2006 Red Hat, Inc. All Rights Reserved.
   5 * Written by David Howells (dhowells@redhat.com)
   6 */
   7
   8#include <linux/module.h>
   9#include <linux/init.h>
  10
  11#include <linux/time.h>
  12#include <linux/kernel.h>
  13#include <linux/mm.h>
  14#include <linux/string.h>
  15#include <linux/stat.h>
  16#include <linux/errno.h>
  17#include <linux/unistd.h>
  18#include <linux/sunrpc/clnt.h>
  19#include <linux/sunrpc/stats.h>
  20#include <linux/nfs_fs.h>
  21#include <linux/nfs_mount.h>
  22#include <linux/lockd/bind.h>
  23#include <linux/seq_file.h>
  24#include <linux/mount.h>
  25#include <linux/vfs.h>
  26#include <linux/namei.h>
  27#include <linux/security.h>
  28
  29#include <linux/uaccess.h>
  30
  31#include "internal.h"
  32
  33#define NFSDBG_FACILITY         NFSDBG_CLIENT
  34
  35/*
  36 * Set the superblock root dentry.
  37 * Note that this function frees the inode in case of error.
  38 */
  39static int nfs_superblock_set_dummy_root(struct super_block *sb, struct inode *inode)
  40{
  41        /* The mntroot acts as the dummy root dentry for this superblock */
  42        if (sb->s_root == NULL) {
  43                sb->s_root = d_make_root(inode);
  44                if (sb->s_root == NULL)
  45                        return -ENOMEM;
  46                ihold(inode);
  47                /*
  48                 * Ensure that this dentry is invisible to d_find_alias().
  49                 * Otherwise, it may be spliced into the tree by
  50                 * d_splice_alias if a parent directory from the same
  51                 * filesystem gets mounted at a later time.
  52                 * This again causes shrink_dcache_for_umount_subtree() to
  53                 * Oops, since the test for IS_ROOT() will fail.
  54                 */
  55                spin_lock(&d_inode(sb->s_root)->i_lock);
  56                spin_lock(&sb->s_root->d_lock);
  57                hlist_del_init(&sb->s_root->d_u.d_alias);
  58                spin_unlock(&sb->s_root->d_lock);
  59                spin_unlock(&d_inode(sb->s_root)->i_lock);
  60        }
  61        return 0;
  62}
  63
  64/*
  65 * get an NFS2/NFS3 root dentry from the root filehandle
  66 */
  67struct dentry *nfs_get_root(struct super_block *sb, struct nfs_fh *mntfh,
  68                            const char *devname)
  69{
  70        struct nfs_server *server = NFS_SB(sb);
  71        struct nfs_fsinfo fsinfo;
  72        struct dentry *ret;
  73        struct inode *inode;
  74        void *name = kstrdup(devname, GFP_KERNEL);
  75        int error;
  76
  77        if (!name)
  78                return ERR_PTR(-ENOMEM);
  79
  80        /* get the actual root for this mount */
  81        fsinfo.fattr = nfs_alloc_fattr();
  82        if (fsinfo.fattr == NULL) {
  83                kfree(name);
  84                return ERR_PTR(-ENOMEM);
  85        }
  86
  87        error = server->nfs_client->rpc_ops->getroot(server, mntfh, &fsinfo);
  88        if (error < 0) {
  89                dprintk("nfs_get_root: getattr error = %d\n", -error);
  90                ret = ERR_PTR(error);
  91                goto out;
  92        }
  93
  94        inode = nfs_fhget(sb, mntfh, fsinfo.fattr, NULL);
  95        if (IS_ERR(inode)) {
  96                dprintk("nfs_get_root: get root inode failed\n");
  97                ret = ERR_CAST(inode);
  98                goto out;
  99        }
 100
 101        error = nfs_superblock_set_dummy_root(sb, inode);
 102        if (error != 0) {
 103                ret = ERR_PTR(error);
 104                goto out;
 105        }
 106
 107        /* root dentries normally start off anonymous and get spliced in later
 108         * if the dentry tree reaches them; however if the dentry already
 109         * exists, we'll pick it up at this point and use it as the root
 110         */
 111        ret = d_obtain_root(inode);
 112        if (IS_ERR(ret)) {
 113                dprintk("nfs_get_root: get root dentry failed\n");
 114                goto out;
 115        }
 116
 117        security_d_instantiate(ret, inode);
 118        spin_lock(&ret->d_lock);
 119        if (IS_ROOT(ret) && !ret->d_fsdata &&
 120            !(ret->d_flags & DCACHE_NFSFS_RENAMED)) {
 121                ret->d_fsdata = name;
 122                name = NULL;
 123        }
 124        spin_unlock(&ret->d_lock);
 125out:
 126        kfree(name);
 127        nfs_free_fattr(fsinfo.fattr);
 128        return ret;
 129}
 130