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