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 <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 }