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/slab.h>
  16 #include <linux/fs.h>
  17 #include <linux/pagemap.h>
  18 #include <linux/mount.h>
  19 #include <linux/namei.h>
  20 #include <linux/mnt_namespace.h>
  21 #include "internal.h"
  22
  23
  24 static struct dentry *afs_mntpt_lookup(struct inode *dir,
  25                                        struct dentry *dentry,
  26                                        struct nameidata *nd);
  27 static int afs_mntpt_open(struct inode *inode, struct file *file);
  28 static void *afs_mntpt_follow_link(struct dentry *dentry, struct nameidata *nd);
  29 static void afs_mntpt_expiry_timed_out(struct work_struct *work);
  30
  31 const struct file_operations afs_mntpt_file_operations = {
  32         .open           = afs_mntpt_open,
  33 };
  34
  35 const struct inode_operations afs_mntpt_inode_operations = {
  36         .lookup         = afs_mntpt_lookup,
  37         .follow_link    = afs_mntpt_follow_link,
  38         .readlink       = page_readlink,
  39         .getattr        = afs_inode_getattr,
  40 };
  41
  42 static LIST_HEAD(afs_vfsmounts);
  43 static DECLARE_DELAYED_WORK(afs_mntpt_expiry_timer, afs_mntpt_expiry_timed_out);
  44
  45 unsigned long afs_mntpt_expiry_timeout = 10 * 60;
  46
  47 /*
  48  * check a symbolic link to see whether it actually encodes a mountpoint
  49  * - sets the AFS_VNODE_MOUNTPOINT flag on the vnode appropriately
  50  */
  51 int afs_mntpt_check_symlink(struct afs_vnode *vnode, struct key *key)
  52 {
  53         struct file file = {
  54                 .private_data = key,
  55         };
  56         struct page *page;
  57         size_t size;
  58         char *buf;
  59         int ret;
  60
  61         _enter("{%u,%u}", 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         wait_on_page_locked(page);
  72         buf = kmap(page);
  73         if (!PageUptodate(page))
  74                 goto out_free;
  75         if (PageError(page))
  76                 goto out_free;
  77
  78         /* examine the symlink's contents */
  79         size = vnode->status.size;
  80         _debug("symlink to %*.*s", (int) size, (int) size, buf);
  81
  82         if (size > 2 &&
  83             (buf[0] == '%' || buf[0] == '#') &&
  84             buf[size - 1] == '.'
  85             ) {
  86                 _debug("symlink is a mountpoint");
  87                 spin_lock(&vnode->lock);
  88                 set_bit(AFS_VNODE_MOUNTPOINT, &vnode->flags);
  89                 spin_unlock(&vnode->lock);
  90         }
  91
  92         ret = 0;
  93
  94 out_free:
  95         kunmap(page);
  96         page_cache_release(page);
  97 out:
  98         _leave(" = %d", ret);
  99         return ret;
 100 }
 101
 102 /*
 103  * no valid lookup procedure on this sort of dir
 104  */
 105 static struct dentry *afs_mntpt_lookup(struct inode *dir,
 106                                        struct dentry *dentry,
 107                                        struct nameidata *nd)
 108 {
 109         _enter("%p,%p{%p{%s},%s}",
 110                dir,
 111                dentry,
 112                dentry->d_parent,
 113                dentry->d_parent ?
 114                dentry->d_parent->d_name.name : (const unsigned char *) "",
 115                dentry->d_name.name);
 116
 117         return ERR_PTR(-EREMOTE);
 118 }
 119
 120 /*
 121  * no valid open procedure on this sort of dir
 122  */
 123 static int afs_mntpt_open(struct inode *inode, struct file *file)
 124 {
 125         _enter("%p,%p{%p{%s},%s}",
 126                inode, file,
 127                file->f_path.dentry->d_parent,
 128                file->f_path.dentry->d_parent ?
 129                file->f_path.dentry->d_parent->d_name.name :
 130                (const unsigned char *) "",
 131                file->f_path.dentry->d_name.name);
 132
 133         return -EREMOTE;
 134 }
 135
 136 /*
 137  * create a vfsmount to be automounted
 138  */
 139 static struct vfsmount *afs_mntpt_do_automount(struct dentry *mntpt)
 140 {
 141         struct afs_super_info *super;
 142         struct vfsmount *mnt;
 143         struct page *page = NULL;
 144         size_t size;
 145         char *buf, *devname = NULL, *options = NULL;
 146         int ret;
 147
 148         _enter("{%s}", mntpt->d_name.name);
 149
 150         BUG_ON(!mntpt->d_inode);
 151
 152         ret = -EINVAL;
 153         size = mntpt->d_inode->i_size;
 154         if (size > PAGE_SIZE - 1)
 155                 goto error;
 156
 157         ret = -ENOMEM;
 158         devname = (char *) get_zeroed_page(GFP_KERNEL);
 159         if (!devname)
 160                 goto error;
 161
 162         options = (char *) get_zeroed_page(GFP_KERNEL);
 163         if (!options)
 164                 goto error;
 165
 166         /* read the contents of the AFS special symlink */
 167         page = read_mapping_page(mntpt->d_inode->i_mapping, 0, NULL);
 168         if (IS_ERR(page)) {
 169                 ret = PTR_ERR(page);
 170                 goto error;
 171         }
 172
 173         ret = -EIO;
 174         wait_on_page_locked(page);
 175         if (!PageUptodate(page) || PageError(page))
 176                 goto error;
 177
 178         buf = kmap(page);
 179         memcpy(devname, buf, size);
 180         kunmap(page);
 181         page_cache_release(page);
 182         page = NULL;
 183
 184         /* work out what options we want */
 185         super = AFS_FS_S(mntpt->d_sb);
 186         memcpy(options, "cell=", 5);
 187         strcpy(options + 5, super->volume->cell->name);
 188         if (super->volume->type == AFSVL_RWVOL)
 189                 strcat(options, ",rwpath");
 190
 191         /* try and do the mount */
 192         _debug("--- attempting mount %s -o %s ---", devname, options);
 193         mnt = vfs_kern_mount(&afs_fs_type, 0, devname, options);
 194         _debug("--- mount result %p ---", mnt);
 195
 196         free_page((unsigned long) devname);
 197         free_page((unsigned long) options);
 198         _leave(" = %p", mnt);
 199         return mnt;
 200
 201 error:
 202         if (page)
 203                 page_cache_release(page);
 204         if (devname)
 205                 free_page((unsigned long) devname);
 206         if (options)
 207                 free_page((unsigned long) options);
 208         _leave(" = %d", ret);
 209         return ERR_PTR(ret);
 210 }
 211
 212 /*
 213  * follow a link from a mountpoint directory, thus causing it to be mounted
 214  */
 215 static void *afs_mntpt_follow_link(struct dentry *dentry, struct nameidata *nd)
 216 {
 217         struct vfsmount *newmnt;
 218         int err;
 219
 220         _enter("%p{%s},{%s:%p{%s},}",
 221                dentry,
 222                dentry->d_name.name,
 223                nd->mnt->mnt_devname,
 224                dentry,
 225                nd->dentry->d_name.name);
 226
 227         dput(nd->dentry);
 228         nd->dentry = dget(dentry);
 229
 230         newmnt = afs_mntpt_do_automount(nd->dentry);
 231         if (IS_ERR(newmnt)) {
 232                 path_release(nd);
 233                 return (void *)newmnt;
 234         }
 235
 236         mntget(newmnt);
 237         err = do_add_mount(newmnt, nd, MNT_SHRINKABLE, &afs_vfsmounts);
 238         switch (err) {
 239         case 0:
 240                 mntput(nd->mnt);
 241                 dput(nd->dentry);
 242                 nd->mnt = newmnt;
 243                 nd->dentry = dget(newmnt->mnt_root);
 244                 schedule_delayed_work(&afs_mntpt_expiry_timer,
 245                                       afs_mntpt_expiry_timeout * HZ);
 246                 break;
 247         case -EBUSY:
 248                 /* someone else made a mount here whilst we were busy */
 249                 while (d_mountpoint(nd->dentry) &&
 250                        follow_down(&nd->mnt, &nd->dentry))
 251                         ;
 252                 err = 0;
 253         default:
 254                 mntput(newmnt);
 255                 break;
 256         }
 257
 258         _leave(" = %d", err);
 259         return ERR_PTR(err);
 260 }
 261
 262 /*
 263  * handle mountpoint expiry timer going off
 264  */
 265 static void afs_mntpt_expiry_timed_out(struct work_struct *work)
 266 {
 267         _enter("");
 268
 269         if (!list_empty(&afs_vfsmounts)) {
 270                 mark_mounts_for_expiry(&afs_vfsmounts);
 271                 schedule_delayed_work(&afs_mntpt_expiry_timer,
 272                                       afs_mntpt_expiry_timeout * HZ);
 273         }
 274
 275         _leave("");
 276 }
 277
 278 /*
 279  * kill the AFS mountpoint timer if it's still running
 280  */
 281 void afs_mntpt_kill_timer(void)
 282 {
 283         _enter("");
 284
 285         ASSERT(list_empty(&afs_vfsmounts));
 286         cancel_delayed_work(&afs_mntpt_expiry_timer);
 287         flush_scheduled_work();
 288 }
 289
 290 /*
 291  * begin unmount by attempting to remove all automounted mountpoints we added
 292  */
 293 void afs_umount_begin(struct vfsmount *vfsmnt, int flags)
 294 {
 295         shrink_submounts(vfsmnt, &afs_vfsmounts);
 296 }