fs/afs/mntpt.c

   1 /* mountpoint management
   2  *
   3  * Copyright (C) 2002 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/kernel.h>
  13 #include <linux/module.h>
  14 #include <linux/init.h>
  15 #include <linux/fs.h>
  16 #include <linux/pagemap.h>
  17 #include <linux/mount.h>
  18 #include <linux/namei.h>
  19 #include <linux/gfp.h>
  20 #include "internal.h"
  21
  22
  23 static struct dentry *afs_mntpt_lookup(struct inode *dir,
  24                                        struct dentry *dentry,
  25                                        struct nameidata *nd);
  26 static int afs_mntpt_open(struct inode *inode, struct file *file);
  27 static void *afs_mntpt_follow_link(struct dentry *dentry, struct nameidata *nd);
  28 static void afs_mntpt_expiry_timed_out(struct work_struct *work);
  29
  30 const struct file_operations afs_mntpt_file_operations = {
  31         .open           = afs_mntpt_open,
  32 };
  33
  34 const struct inode_operations afs_mntpt_inode_operations = {
  35         .lookup         = afs_mntpt_lookup,
  36         .follow_link    = afs_mntpt_follow_link,
  37         .readlink       = page_readlink,
  38         .getattr        = afs_getattr,
  39 };
  40
  41 static LIST_HEAD(afs_vfsmounts);
  42 static DECLARE_DELAYED_WORK(afs_mntpt_expiry_timer, afs_mntpt_expiry_timed_out);
  43
  44 static unsigned long afs_mntpt_expiry_timeout = 10 * 60;
  45
  46 /*
  47  * check a symbolic link to see whether it actually encodes a mountpoint
  48  * - sets the AFS_VNODE_MOUNTPOINT flag on the vnode appropriately
  49  */
  50 int afs_mntpt_check_symlink(struct afs_vnode *vnode, struct key *key)
  51 {
  52         struct file file = {
  53                 .private_data = key,
  54         };
  55         struct page *page;
  56         size_t size;
  57         char *buf;
  58         int ret;
  59
  60         _enter("{%x:%u,%u}",
  61                vnode->fid.vid, vnode->fid.vnode, vnode->fid.unique);
  62
  63         /* read the contents of the symlink into the pagecache */
  64         page = read_mapping_page(AFS_VNODE_TO_I(vnode)->i_mapping, 0, &file);
  65         if (IS_ERR(page)) {
  66                 ret = PTR_ERR(page);
  67                 goto out;
  68         }
  69
  70         ret = -EIO;
  71         if (PageError(page))
  72                 goto out_free;
  73
  74         buf = kmap(page);
  75
  76         /* examine the symlink's contents */
  77         size = vnode->status.size;
  78         _debug("symlink to %*.*s", (int) size, (int) size, buf);
  79
  80         if (size > 2 &&
  81             (buf[0] == '%' || buf[0] == '#') &&
  82             buf[size - 1] == '.'
  83             ) {
  84                 _debug("symlink is a mountpoint");
  85                 spin_lock(&vnode->lock);
  86                 set_bit(AFS_VNODE_MOUNTPOINT, &vnode->flags);
  87                 spin_unlock(&vnode->lock);
  88         }
  89
  90         ret = 0;
  91
  92         kunmap(page);
  93 out_free:
  94         page_cache_release(page);
  95 out:
  96         _leave(" = %d", ret);
  97         return ret;
  98 }
  99
 100 /*
 101  * no valid lookup procedure on this sort of dir
 102  */
 103 static struct dentry *afs_mntpt_lookup(struct inode *dir,
 104                                        struct dentry *dentry,
 105                                        struct nameidata *nd)
 106 {
 107         _enter("%p,%p{%p{%s},%s}",
 108                dir,
 109                dentry,
 110                dentry->d_parent,
 111                dentry->d_parent ?
 112                dentry->d_parent->d_name.name : (const unsigned char *) "",
 113                dentry->d_name.name);
 114
 115         return ERR_PTR(-EREMOTE);
 116 }
 117
 118 /*
 119  * no valid open procedure on this sort of dir
 120  */
 121 static int afs_mntpt_open(struct inode *inode, struct file *file)
 122 {
 123         _enter("%p,%p{%p{%s},%s}",
 124                inode, file,
 125                file->f_path.dentry->d_parent,
 126                file->f_path.dentry->d_parent ?
 127                file->f_path.dentry->d_parent->d_name.name :
 128                (const unsigned char *) "",
 129                file->f_path.dentry->d_name.name);
 130
 131         return -EREMOTE;
 132 }
 133
 134 /*
 135  * create a vfsmount to be automounted
 136  */
 137 static struct vfsmount *afs_mntpt_do_automount(struct dentry *mntpt)
 138 {
 139         struct afs_super_info *super;
 140         struct vfsmount *mnt;
 141         struct page *page;
 142         size_t size;
 143         char *buf, *devname, *options;
 144         int ret;
 145
 146         _enter("{%s}", mntpt->d_name.name);
 147
 148         BUG_ON(!mntpt->d_inode);
 149
 150         ret = -EINVAL;
 151         size = mntpt->d_inode->i_size;
 152         if (size > PAGE_SIZE - 1)
 153                 goto error_no_devname;
 154
 155         ret = -ENOMEM;
 156         devname = (char *) get_zeroed_page(GFP_KERNEL);
 157         if (!devname)
 158                 goto error_no_devname;
 159
 160         options = (char *) get_zeroed_page(GFP_KERNEL);
 161         if (!options)
 162                 goto error_no_options;
 163
 164         /* read the contents of the AFS special symlink */
 165         page = read_mapping_page(mntpt->d_inode->i_mapping, 0, NULL);
 166         if (IS_ERR(page)) {
 167                 ret = PTR_ERR(page);
 168                 goto error_no_page;
 169         }
 170
 171         ret = -EIO;
 172         if (PageError(page))
 173                 goto error;
 174
 175         buf = kmap_atomic(page, KM_USER0);
 176         memcpy(devname, buf, size);
 177         kunmap_atomic(buf, KM_USER0);
 178         page_cache_release(page);
 179         page = NULL;
 180
 181         /* work out what options we want */
 182         super = AFS_FS_S(mntpt->d_sb);
 183         memcpy(options, "cell=", 5);
 184         strcpy(options + 5, super->volume->cell->name);
 185         if (super->volume->type == AFSVL_RWVOL)
 186                 strcat(options, ",rwpath");
 187
 188         /* try and do the mount */
 189         _debug("--- attempting mount %s -o %s ---", devname, options);
 190         mnt = vfs_kern_mount(&afs_fs_type, 0, devname, options);
 191         _debug("--- mount result %p ---", mnt);
 192
 193         free_page((unsigned long) devname);
 194         free_page((unsigned long) options);
 195         _leave(" = %p", mnt);
 196         return mnt;
 197
 198 error:
 199         page_cache_release(page);
 200 error_no_page:
 201         free_page((unsigned long) options);
 202 error_no_options:
 203         free_page((unsigned long) devname);
 204 error_no_devname:
 205         _leave(" = %d", ret);
 206         return ERR_PTR(ret);
 207 }
 208
 209 /*
 210  * follow a link from a mountpoint directory, thus causing it to be mounted
 211  */
 212 static void *afs_mntpt_follow_link(struct dentry *dentry, struct nameidata *nd)
 213 {
 214         struct vfsmount *newmnt;
 215         int err;
 216
 217         _enter("%p{%s},{%s:%p{%s},}",
 218                dentry,
 219                dentry->d_name.name,
 220                nd->path.mnt->mnt_devname,
 221                dentry,
 222                nd->path.dentry->d_name.name);
 223
 224         dput(nd->path.dentry);
 225         nd->path.dentry = dget(dentry);
 226
 227         newmnt = afs_mntpt_do_automount(nd->path.dentry);
 228         if (IS_ERR(newmnt)) {
 229                 path_put(&nd->path);
 230                 return (void *)newmnt;
 231         }
 232
 233         mntget(newmnt);
 234         err = do_add_mount(newmnt, &nd->path, MNT_SHRINKABLE, &afs_vfsmounts);
 235         switch (err) {
 236         case 0:
 237                 path_put(&nd->path);
 238                 nd->path.mnt = newmnt;
 239                 nd->path.dentry = dget(newmnt->mnt_root);
 240                 schedule_delayed_work(&afs_mntpt_expiry_timer,
 241                                       afs_mntpt_expiry_timeout * HZ);
 242                 break;
 243         case -EBUSY:
 244                 /* someone else made a mount here whilst we were busy */
 245                 while (d_mountpoint(nd->path.dentry) &&
 246                        follow_down(&nd->path))
 247                         ;
 248                 err = 0;
 249         default:
 250                 mntput(newmnt);
 251                 break;
 252         }
 253
 254         _leave(" = %d", err);
 255         return ERR_PTR(err);
 256 }
 257
 258 /*
 259  * handle mountpoint expiry timer going off
 260  */
 261 static void afs_mntpt_expiry_timed_out(struct work_struct *work)
 262 {
 263         _enter("");
 264
 265         if (!list_empty(&afs_vfsmounts)) {
 266                 mark_mounts_for_expiry(&afs_vfsmounts);
 267                 schedule_delayed_work(&afs_mntpt_expiry_timer,
 268                                       afs_mntpt_expiry_timeout * HZ);
 269         }
 270
 271         _leave("");
 272 }
 273
 274 /*
 275  * kill the AFS mountpoint timer if it's still running
 276  */
 277 void afs_mntpt_kill_timer(void)
 278 {
 279         _enter("");
 280
 281         ASSERT(list_empty(&afs_vfsmounts));
 282         cancel_delayed_work(&afs_mntpt_expiry_timer);
 283         flush_scheduled_work();
 284 }