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_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("{%x:%u,%u}",
  62                vnode->fid.vid, vnode->fid.vnode, vnode->fid.unique);
  63
  64         /* read the contents of the symlink into the pagecache */
  65         page = read_mapping_page(AFS_VNODE_TO_I(vnode)->i_mapping, 0, &file);
  66         if (IS_ERR(page)) {
  67                 ret = PTR_ERR(page);
  68                 goto out;
  69         }
  70
  71         ret = -EIO;
  72         if (PageError(page))
  73                 goto out_free;
  74
  75         buf = kmap(page);
  76
  77         /* examine the symlink's contents */
  78         size = vnode->status.size;
  79         _debug("symlink to %*.*s", (int) size, (int) size, buf);
  80
  81         if (size > 2 &&
  82             (buf[0] == '%' || buf[0] == '#') &&
  83             buf[size - 1] == '.'
  84             ) {
  85                 _debug("symlink is a mountpoint");
  86                 spin_lock(&vnode->lock);
  87                 set_bit(AFS_VNODE_MOUNTPOINT, &vnode->flags);
  88                 spin_unlock(&vnode->lock);
  89         }
  90
  91         ret = 0;
  92
  93         kunmap(page);
  94 out_free:
  95         page_cache_release(page);
  96 out:
  97         _leave(" = %d", ret);
  98         return ret;
  99 }
 100
 101 /*
 102  * no valid lookup procedure on this sort of dir
 103  */
 104 static struct dentry *afs_mntpt_lookup(struct inode *dir,
 105                                        struct dentry *dentry,
 106                                        struct nameidata *nd)
 107 {
 108         _enter("%p,%p{%p{%s},%s}",
 109                dir,
 110                dentry,
 111                dentry->d_parent,
 112                dentry->d_parent ?
 113                dentry->d_parent->d_name.name : (const unsigned char *) "",
 114                dentry->d_name.name);
 115
 116         return ERR_PTR(-EREMOTE);
 117 }
 118
 119 /*
 120  * no valid open procedure on this sort of dir
 121  */
 122 static int afs_mntpt_open(struct inode *inode, struct file *file)
 123 {
 124         _enter("%p,%p{%p{%s},%s}",
 125                inode, file,
 126                file->f_path.dentry->d_parent,
 127                file->f_path.dentry->d_parent ?
 128                file->f_path.dentry->d_parent->d_name.name :
 129                (const unsigned char *) "",
 130                file->f_path.dentry->d_name.name);
 131
 132         return -EREMOTE;
 133 }
 134
 135 /*
 136  * create a vfsmount to be automounted
 137  */
 138 static struct vfsmount *afs_mntpt_do_automount(struct dentry *mntpt)
 139 {
 140         struct afs_super_info *super;
 141         struct vfsmount *mnt;
 142         struct page *page = NULL;
 143         size_t size;
 144         char *buf, *devname = NULL, *options = NULL;
 145         int ret;
 146
 147         _enter("{%s}", mntpt->d_name.name);
 148
 149         BUG_ON(!mntpt->d_inode);
 150
 151         ret = -EINVAL;
 152         size = mntpt->d_inode->i_size;
 153         if (size > PAGE_SIZE - 1)
 154                 goto error;
 155
 156         ret = -ENOMEM;
 157         devname = (char *) get_zeroed_page(GFP_KERNEL);
 158         if (!devname)
 159                 goto error;
 160
 161         options = (char *) get_zeroed_page(GFP_KERNEL);
 162         if (!options)
 163                 goto error;
 164
 165         /* read the contents of the AFS special symlink */
 166         page = read_mapping_page(mntpt->d_inode->i_mapping, 0, NULL);
 167         if (IS_ERR(page)) {
 168                 ret = PTR_ERR(page);
 169                 goto error;
 170         }
 171
 172         ret = -EIO;
 173         if (PageError(page))
 174                 goto error;
 175
 176         buf = kmap(page);
 177         memcpy(devname, buf, size);
 178         kunmap(page);
 179         page_cache_release(page);
 180         page = NULL;
 181
 182         /* work out what options we want */
 183         super = AFS_FS_S(mntpt->d_sb);
 184         memcpy(options, "cell=", 5);
 185         strcpy(options + 5, super->volume->cell->name);
 186         if (super->volume->type == AFSVL_RWVOL)
 187                 strcat(options, ",rwpath");
 188
 189         /* try and do the mount */
 190         _debug("--- attempting mount %s -o %s ---", devname, options);
 191         mnt = vfs_kern_mount(&afs_fs_type, 0, devname, options);
 192         _debug("--- mount result %p ---", mnt);
 193
 194         free_page((unsigned long) devname);
 195         free_page((unsigned long) options);
 196         _leave(" = %p", mnt);
 197         return mnt;
 198
 199 error:
 200         if (page)
 201                 page_cache_release(page);
 202         if (devname)
 203                 free_page((unsigned long) devname);
 204         if (options)
 205                 free_page((unsigned long) options);
 206         _leave(" = %d", ret);
 207         return ERR_PTR(ret);
 208 }
 209
 210 /*
 211  * follow a link from a mountpoint directory, thus causing it to be mounted
 212  */
 213 static void *afs_mntpt_follow_link(struct dentry *dentry, struct nameidata *nd)
 214 {
 215         struct vfsmount *newmnt;
 216         int err;
 217
 218         _enter("%p{%s},{%s:%p{%s},}",
 219                dentry,
 220                dentry->d_name.name,
 221                nd->mnt->mnt_devname,
 222                dentry,
 223                nd->dentry->d_name.name);
 224
 225         dput(nd->dentry);
 226         nd->dentry = dget(dentry);
 227
 228         newmnt = afs_mntpt_do_automount(nd->dentry);
 229         if (IS_ERR(newmnt)) {
 230                 path_release(nd);
 231                 return (void *)newmnt;
 232         }
 233
 234         mntget(newmnt);
 235         err = do_add_mount(newmnt, nd, MNT_SHRINKABLE, &afs_vfsmounts);
 236         switch (err) {
 237         case 0:
 238                 mntput(nd->mnt);
 239                 dput(nd->dentry);
 240                 nd->mnt = newmnt;
 241                 nd->dentry = dget(newmnt->mnt_root);
 242                 schedule_delayed_work(&afs_mntpt_expiry_timer,
 243                                       afs_mntpt_expiry_timeout * HZ);
 244                 break;
 245         case -EBUSY:
 246                 /* someone else made a mount here whilst we were busy */
 247                 while (d_mountpoint(nd->dentry) &&
 248                        follow_down(&nd->mnt, &nd->dentry))
 249                         ;
 250                 err = 0;
 251         default:
 252                 mntput(newmnt);
 253                 break;
 254         }
 255
 256         _leave(" = %d", err);
 257         return ERR_PTR(err);
 258 }
 259
 260 /*
 261  * handle mountpoint expiry timer going off
 262  */
 263 static void afs_mntpt_expiry_timed_out(struct work_struct *work)
 264 {
 265         _enter("");
 266
 267         if (!list_empty(&afs_vfsmounts)) {
 268                 mark_mounts_for_expiry(&afs_vfsmounts);
 269                 schedule_delayed_work(&afs_mntpt_expiry_timer,
 270                                       afs_mntpt_expiry_timeout * HZ);
 271         }
 272
 273         _leave("");
 274 }
 275
 276 /*
 277  * kill the AFS mountpoint timer if it's still running
 278  */
 279 void afs_mntpt_kill_timer(void)
 280 {
 281         _enter("");
 282
 283         ASSERT(list_empty(&afs_vfsmounts));
 284         cancel_delayed_work(&afs_mntpt_expiry_timer);
 285         flush_scheduled_work();
 286 }
 287
 288 /*
 289  * begin unmount by attempting to remove all automounted mountpoints we added
 290  */
 291 void afs_umount_begin(struct vfsmount *vfsmnt, int flags)
 292 {
 293         shrink_submounts(vfsmnt, &afs_vfsmounts);
 294 }