fs/pnode.c

   1 /*
   2  *  linux/fs/pnode.c
   3  *
   4  * (C) Copyright IBM Corporation 2005.
   5  *      Released under GPL v2.
   6  *      Author : Ram Pai (linuxram@us.ibm.com)
   7  *
   8  */
   9 #include <linux/mnt_namespace.h>
  10 #include <linux/mount.h>
  11 #include <linux/fs.h>
  12 #include "internal.h"
  13 #include "pnode.h"
  14
  15 /* return the next shared peer mount of @p */
  16 static inline struct vfsmount *next_peer(struct vfsmount *p)
  17 {
  18         return list_entry(p->mnt_share.next, struct vfsmount, mnt_share);
  19 }
  20
  21 static inline struct vfsmount *first_slave(struct vfsmount *p)
  22 {
  23         return list_entry(p->mnt_slave_list.next, struct vfsmount, mnt_slave);
  24 }
  25
  26 static inline struct vfsmount *next_slave(struct vfsmount *p)
  27 {
  28         return list_entry(p->mnt_slave.next, struct vfsmount, mnt_slave);
  29 }
  30
  31 /*
  32  * Return true if path is reachable from root
  33  *
  34  * namespace_sem is held, and mnt is attached
  35  */
  36 static bool is_path_reachable(struct vfsmount *mnt, struct dentry *dentry,
  37                          const struct path *root)
  38 {
  39         while (mnt != root->mnt && mnt->mnt_parent != mnt) {
  40                 dentry = mnt->mnt_mountpoint;
  41                 mnt = mnt->mnt_parent;
  42         }
  43         return mnt == root->mnt && is_subdir(dentry, root->dentry);
  44 }
  45
  46 static struct vfsmount *get_peer_under_root(struct vfsmount *mnt,
  47                                             struct mnt_namespace *ns,
  48                                             const struct path *root)
  49 {
  50         struct vfsmount *m = mnt;
  51
  52         do {
  53                 /* Check the namespace first for optimization */
  54                 if (m->mnt_ns == ns && is_path_reachable(m, m->mnt_root, root))
  55                         return m;
  56
  57                 m = next_peer(m);
  58         } while (m != mnt);
  59
  60         return NULL;
  61 }
  62
  63 /*
  64  * Get ID of closest dominating peer group having a representative
  65  * under the given root.
  66  *
  67  * Caller must hold namespace_sem
  68  */
  69 int get_dominating_id(struct vfsmount *mnt, const struct path *root)
  70 {
  71         struct vfsmount *m;
  72
  73         for (m = mnt->mnt_master; m != NULL; m = m->mnt_master) {
  74                 struct vfsmount *d = get_peer_under_root(m, mnt->mnt_ns, root);
  75                 if (d)
  76                         return d->mnt_group_id;
  77         }
  78
  79         return 0;
  80 }
  81
  82 static int do_make_slave(struct vfsmount *mnt)
  83 {
  84         struct vfsmount *peer_mnt = mnt, *master = mnt->mnt_master;
  85         struct vfsmount *slave_mnt;
  86
  87         /*
  88          * slave 'mnt' to a peer mount that has the
  89          * same root dentry. If none is available then
  90          * slave it to anything that is available.
  91          */
  92         while ((peer_mnt = next_peer(peer_mnt)) != mnt &&
  93                peer_mnt->mnt_root != mnt->mnt_root) ;
  94
  95         if (peer_mnt == mnt) {
  96                 peer_mnt = next_peer(mnt);
  97                 if (peer_mnt == mnt)
  98                         peer_mnt = NULL;
  99         }
 100         if (IS_MNT_SHARED(mnt) && list_empty(&mnt->mnt_share))
 101                 mnt_release_group_id(mnt);
 102
 103         list_del_init(&mnt->mnt_share);
 104         mnt->mnt_group_id = 0;
 105
 106         if (peer_mnt)
 107                 master = peer_mnt;
 108
 109         if (master) {
 110                 list_for_each_entry(slave_mnt, &mnt->mnt_slave_list, mnt_slave)
 111                         slave_mnt->mnt_master = master;
 112                 list_move(&mnt->mnt_slave, &master->mnt_slave_list);
 113                 list_splice(&mnt->mnt_slave_list, master->mnt_slave_list.prev);
 114                 INIT_LIST_HEAD(&mnt->mnt_slave_list);
 115         } else {
 116                 struct list_head *p = &mnt->mnt_slave_list;
 117                 while (!list_empty(p)) {
 118                         slave_mnt = list_first_entry(p,
 119                                         struct vfsmount, mnt_slave);
 120                         list_del_init(&slave_mnt->mnt_slave);
 121                         slave_mnt->mnt_master = NULL;
 122                 }
 123         }
 124         mnt->mnt_master = master;
 125         CLEAR_MNT_SHARED(mnt);
 126         return 0;
 127 }
 128
 129 /*
 130  * vfsmount lock must be held for write
 131  */
 132 void change_mnt_propagation(struct vfsmount *mnt, int type)
 133 {
 134         if (type == MS_SHARED) {
 135                 set_mnt_shared(mnt);
 136                 return;
 137         }
 138         do_make_slave(mnt);
 139         if (type != MS_SLAVE) {
 140                 list_del_init(&mnt->mnt_slave);
 141                 mnt->mnt_master = NULL;
 142                 if (type == MS_UNBINDABLE)
 143                         mnt->mnt_flags |= MNT_UNBINDABLE;
 144                 else
 145                         mnt->mnt_flags &= ~MNT_UNBINDABLE;
 146         }
 147 }
 148
 149 /*
 150  * get the next mount in the propagation tree.
 151  * @m: the mount seen last
 152  * @origin: the original mount from where the tree walk initiated
 153  *
 154  * Note that peer groups form contiguous segments of slave lists.
 155  * We rely on that in get_source() to be able to find out if
 156  * vfsmount found while iterating with propagation_next() is
 157  * a peer of one we'd found earlier.
 158  */
 159 static struct vfsmount *propagation_next(struct vfsmount *m,
 160                                          struct vfsmount *origin)
 161 {
 162         /* are there any slaves of this mount? */
 163         if (!IS_MNT_NEW(m) && !list_empty(&m->mnt_slave_list))
 164                 return first_slave(m);
 165
 166         while (1) {
 167                 struct vfsmount *next;
 168                 struct vfsmount *master = m->mnt_master;
 169
 170                 if (master == origin->mnt_master) {
 171                         next = next_peer(m);
 172                         return ((next == origin) ? NULL : next);
 173                 } else if (m->mnt_slave.next != &master->mnt_slave_list)
 174                         return next_slave(m);
 175
 176                 /* back at master */
 177                 m = master;
 178         }
 179 }
 180
 181 /*
 182  * return the source mount to be used for cloning
 183  *
 184  * @dest        the current destination mount
 185  * @last_dest   the last seen destination mount
 186  * @last_src    the last seen source mount
 187  * @type        return CL_SLAVE if the new mount has to be
 188  *              cloned as a slave.
 189  */
 190 static struct vfsmount *get_source(struct vfsmount *dest,
 191                                         struct vfsmount *last_dest,
 192                                         struct vfsmount *last_src,
 193                                         int *type)
 194 {
 195         struct vfsmount *p_last_src = NULL;
 196         struct vfsmount *p_last_dest = NULL;
 197
 198         while (last_dest != dest->mnt_master) {
 199                 p_last_dest = last_dest;
 200                 p_last_src = last_src;
 201                 last_dest = last_dest->mnt_master;
 202                 last_src = last_src->mnt_master;
 203         }
 204
 205         if (p_last_dest) {
 206                 do {
 207                         p_last_dest = next_peer(p_last_dest);
 208                 } while (IS_MNT_NEW(p_last_dest));
 209                 /* is that a peer of the earlier? */
 210                 if (dest == p_last_dest) {
 211                         *type = CL_MAKE_SHARED;
 212                         return p_last_src;
 213                 }
 214         }
 215         /* slave of the earlier, then */
 216         *type = CL_SLAVE;
 217         /* beginning of peer group among the slaves? */
 218         if (IS_MNT_SHARED(dest))
 219                 *type |= CL_MAKE_SHARED;
 220         return last_src;
 221 }
 222
 223 /*
 224  * mount 'source_mnt' under the destination 'dest_mnt' at
 225  * dentry 'dest_dentry'. And propagate that mount to
 226  * all the peer and slave mounts of 'dest_mnt'.
 227  * Link all the new mounts into a propagation tree headed at
 228  * source_mnt. Also link all the new mounts using ->mnt_list
 229  * headed at source_mnt's ->mnt_list
 230  *
 231  * @dest_mnt: destination mount.
 232  * @dest_dentry: destination dentry.
 233  * @source_mnt: source mount.
 234  * @tree_list : list of heads of trees to be attached.
 235  */
 236 int propagate_mnt(struct vfsmount *dest_mnt, struct dentry *dest_dentry,
 237                     struct vfsmount *source_mnt, struct list_head *tree_list)
 238 {
 239         struct vfsmount *m, *child;
 240         int ret = 0;
 241         struct vfsmount *prev_dest_mnt = dest_mnt;
 242         struct vfsmount *prev_src_mnt  = source_mnt;
 243         LIST_HEAD(tmp_list);
 244         LIST_HEAD(umount_list);
 245
 246         for (m = propagation_next(dest_mnt, dest_mnt); m;
 247                         m = propagation_next(m, dest_mnt)) {
 248                 int type;
 249                 struct vfsmount *source;
 250
 251                 if (IS_MNT_NEW(m))
 252                         continue;
 253
 254                 source =  get_source(m, prev_dest_mnt, prev_src_mnt, &type);
 255
 256                 if (!(child = copy_tree(source, source->mnt_root, type))) {
 257                         ret = -ENOMEM;
 258                         list_splice(tree_list, tmp_list.prev);
 259                         goto out;
 260                 }
 261
 262                 if (is_subdir(dest_dentry, m->mnt_root)) {
 263                         mnt_set_mountpoint(m, dest_dentry, child);
 264                         list_add_tail(&child->mnt_hash, tree_list);
 265                 } else {
 266                         /*
 267                          * This can happen if the parent mount was bind mounted
 268                          * on some subdirectory of a shared/slave mount.
 269                          */
 270                         list_add_tail(&child->mnt_hash, &tmp_list);
 271                 }
 272                 prev_dest_mnt = m;
 273                 prev_src_mnt  = child;
 274         }
 275 out:
 276         br_write_lock(vfsmount_lock);
 277         while (!list_empty(&tmp_list)) {
 278                 child = list_first_entry(&tmp_list, struct vfsmount, mnt_hash);
 279                 umount_tree(child, 0, &umount_list);
 280         }
 281         br_write_unlock(vfsmount_lock);
 282         release_mounts(&umount_list);
 283         return ret;
 284 }
 285
 286 /*
 287  * return true if the refcount is greater than count
 288  */
 289 static inline int do_refcount_check(struct vfsmount *mnt, int count)
 290 {
 291         int mycount = atomic_read(&mnt->mnt_count) - mnt->mnt_ghosts;
 292         return (mycount > count);
 293 }
 294
 295 /*
 296  * check if the mount 'mnt' can be unmounted successfully.
 297  * @mnt: the mount to be checked for unmount
 298  * NOTE: unmounting 'mnt' would naturally propagate to all
 299  * other mounts its parent propagates to.
 300  * Check if any of these mounts that **do not have submounts**
 301  * have more references than 'refcnt'. If so return busy.
 302  *
 303  * vfsmount lock must be held for read or write
 304  */
 305 int propagate_mount_busy(struct vfsmount *mnt, int refcnt)
 306 {
 307         struct vfsmount *m, *child;
 308         struct vfsmount *parent = mnt->mnt_parent;
 309         int ret = 0;
 310
 311         if (mnt == parent)
 312                 return do_refcount_check(mnt, refcnt);
 313
 314         /*
 315          * quickly check if the current mount can be unmounted.
 316          * If not, we don't have to go checking for all other
 317          * mounts
 318          */
 319         if (!list_empty(&mnt->mnt_mounts) || do_refcount_check(mnt, refcnt))
 320                 return 1;
 321
 322         for (m = propagation_next(parent, parent); m;
 323                         m = propagation_next(m, parent)) {
 324                 child = __lookup_mnt(m, mnt->mnt_mountpoint, 0);
 325                 if (child && list_empty(&child->mnt_mounts) &&
 326                     (ret = do_refcount_check(child, 1)))
 327                         break;
 328         }
 329         return ret;
 330 }
 331
 332 /*
 333  * NOTE: unmounting 'mnt' naturally propagates to all other mounts its
 334  * parent propagates to.
 335  */
 336 static void __propagate_umount(struct vfsmount *mnt)
 337 {
 338         struct vfsmount *parent = mnt->mnt_parent;
 339         struct vfsmount *m;
 340
 341         BUG_ON(parent == mnt);
 342
 343         for (m = propagation_next(parent, parent); m;
 344                         m = propagation_next(m, parent)) {
 345
 346                 struct vfsmount *child = __lookup_mnt(m,
 347                                         mnt->mnt_mountpoint, 0);
 348                 /*
 349                  * umount the child only if the child has no
 350                  * other children
 351                  */
 352                 if (child && list_empty(&child->mnt_mounts))
 353                         list_move_tail(&child->mnt_hash, &mnt->mnt_hash);
 354         }
 355 }
 356
 357 /*
 358  * collect all mounts that receive propagation from the mount in @list,
 359  * and return these additional mounts in the same list.
 360  * @list: the list of mounts to be unmounted.
 361  *
 362  * vfsmount lock must be held for write
 363  */
 364 int propagate_umount(struct list_head *list)
 365 {
 366         struct vfsmount *mnt;
 367
 368         list_for_each_entry(mnt, list, mnt_hash)
 369                 __propagate_umount(mnt);
 370         return 0;
 371 }