fs/nfs/getroot.c

   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 }