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 "pnode.h"
  13
  14 /* return the next shared peer mount of @p */
  15 static inline struct vfsmount *next_peer(struct vfsmount *p)
  16 {
  17         return list_entry(p->mnt_share.next, struct vfsmount, mnt_share);
  18 }
  19
  20 static inline struct vfsmount *first_slave(struct vfsmount *p)
  21 {
  22         return list_entry(p->mnt_slave_list.next, struct vfsmount, mnt_slave);
  23 }
  24
  25 static inline struct vfsmount *next_slave(struct vfsmount *p)
  26 {
  27         return list_entry(p->mnt_slave.next, struct vfsmount, mnt_slave);
  28 }
  29
  30 static int do_make_slave(struct vfsmount *mnt)
  31 {
  32         struct vfsmount *peer_mnt = mnt, *master = mnt->mnt_master;
  33         struct vfsmount *slave_mnt;
  34
  35         /*
  36          * slave 'mnt' to a peer mount that has the
  37          * same root dentry. If none is available than
  38          * slave it to anything that is available.
  39          */
  40         while ((peer_mnt = next_peer(peer_mnt)) != mnt &&
  41                peer_mnt->mnt_root != mnt->mnt_root) ;
  42
  43         if (peer_mnt == mnt) {
  44                 peer_mnt = next_peer(mnt);
  45                 if (peer_mnt == mnt)
  46                         peer_mnt = NULL;
  47         }
  48         list_del_init(&mnt->mnt_share);
  49
  50         if (peer_mnt)
  51                 master = peer_mnt;
  52
  53         if (master) {
  54                 list_for_each_entry(slave_mnt, &mnt->mnt_slave_list, mnt_slave)
  55                         slave_mnt->mnt_master = master;
  56                 list_move(&mnt->mnt_slave, &master->mnt_slave_list);
  57                 list_splice(&mnt->mnt_slave_list, master->mnt_slave_list.prev);
  58                 INIT_LIST_HEAD(&mnt->mnt_slave_list);
  59         } else {
  60                 struct list_head *p = &mnt->mnt_slave_list;
  61                 while (!list_empty(p)) {
  62                         slave_mnt = list_entry(p->next,
  63                                         struct vfsmount, mnt_slave);
  64                         list_del_init(&slave_mnt->mnt_slave);
  65                         slave_mnt->mnt_master = NULL;
  66                 }
  67         }
  68         mnt->mnt_master = master;
  69         CLEAR_MNT_SHARED(mnt);
  70         INIT_LIST_HEAD(&mnt->mnt_slave_list);
  71         return 0;
  72 }
  73
  74 void change_mnt_propagation(struct vfsmount *mnt, int type)
  75 {
  76         if (type == MS_SHARED) {
  77                 set_mnt_shared(mnt);
  78                 return;
  79         }
  80         do_make_slave(mnt);
  81         if (type != MS_SLAVE) {
  82                 list_del_init(&mnt->mnt_slave);
  83                 mnt->mnt_master = NULL;
  84                 if (type == MS_UNBINDABLE)
  85                         mnt->mnt_flags |= MNT_UNBINDABLE;
  86         }
  87 }
  88
  89 /*
  90  * get the next mount in the propagation tree.
  91  * @m: the mount seen last
  92  * @origin: the original mount from where the tree walk initiated
  93  */
  94 static struct vfsmount *propagation_next(struct vfsmount *m,
  95                                          struct vfsmount *origin)
  96 {
  97         /* are there any slaves of this mount? */
  98         if (!IS_MNT_NEW(m) && !list_empty(&m->mnt_slave_list))
  99                 return first_slave(m);
 100
 101         while (1) {
 102                 struct vfsmount *next;
 103                 struct vfsmount *master = m->mnt_master;
 104
 105                 if (master == origin->mnt_master) {
 106                         next = next_peer(m);
 107                         return ((next == origin) ? NULL : next);
 108                 } else if (m->mnt_slave.next != &master->mnt_slave_list)
 109                         return next_slave(m);
 110
 111                 /* back at master */
 112                 m = master;
 113         }
 114 }
 115
 116 /*
 117  * return the source mount to be used for cloning
 118  *
 119  * @dest        the current destination mount
 120  * @last_dest   the last seen destination mount
 121  * @last_src    the last seen source mount
 122  * @type        return CL_SLAVE if the new mount has to be
 123  *              cloned as a slave.
 124  */
 125 static struct vfsmount *get_source(struct vfsmount *dest,
 126                                         struct vfsmount *last_dest,
 127                                         struct vfsmount *last_src,
 128                                         int *type)
 129 {
 130         struct vfsmount *p_last_src = NULL;
 131         struct vfsmount *p_last_dest = NULL;
 132         *type = CL_PROPAGATION;
 133
 134         if (IS_MNT_SHARED(dest))
 135                 *type |= CL_MAKE_SHARED;
 136
 137         while (last_dest != dest->mnt_master) {
 138                 p_last_dest = last_dest;
 139                 p_last_src = last_src;
 140                 last_dest = last_dest->mnt_master;
 141                 last_src = last_src->mnt_master;
 142         }
 143
 144         if (p_last_dest) {
 145                 do {
 146                         p_last_dest = next_peer(p_last_dest);
 147                 } while (IS_MNT_NEW(p_last_dest));
 148         }
 149
 150         if (dest != p_last_dest) {
 151                 *type |= CL_SLAVE;
 152                 return last_src;
 153         } else
 154                 return p_last_src;
 155 }
 156
 157 /*
 158  * mount 'source_mnt' under the destination 'dest_mnt' at
 159  * dentry 'dest_dentry'. And propagate that mount to
 160  * all the peer and slave mounts of 'dest_mnt'.
 161  * Link all the new mounts into a propagation tree headed at
 162  * source_mnt. Also link all the new mounts using ->mnt_list
 163  * headed at source_mnt's ->mnt_list
 164  *
 165  * @dest_mnt: destination mount.
 166  * @dest_dentry: destination dentry.
 167  * @source_mnt: source mount.
 168  * @tree_list : list of heads of trees to be attached.
 169  */
 170 int propagate_mnt(struct vfsmount *dest_mnt, struct dentry *dest_dentry,
 171                     struct vfsmount *source_mnt, struct list_head *tree_list)
 172 {
 173         struct vfsmount *m, *child;
 174         int ret = 0;
 175         struct vfsmount *prev_dest_mnt = dest_mnt;
 176         struct vfsmount *prev_src_mnt  = source_mnt;
 177         LIST_HEAD(tmp_list);
 178         LIST_HEAD(umount_list);
 179
 180         for (m = propagation_next(dest_mnt, dest_mnt); m;
 181                         m = propagation_next(m, dest_mnt)) {
 182                 int type;
 183                 struct vfsmount *source;
 184
 185                 if (IS_MNT_NEW(m))
 186                         continue;
 187
 188                 source =  get_source(m, prev_dest_mnt, prev_src_mnt, &type);
 189
 190                 if (!(child = copy_tree(source, source->mnt_root, type))) {
 191                         ret = -ENOMEM;
 192                         list_splice(tree_list, tmp_list.prev);
 193                         goto out;
 194                 }
 195
 196                 if (is_subdir(dest_dentry, m->mnt_root)) {
 197                         mnt_set_mountpoint(m, dest_dentry, child);
 198                         list_add_tail(&child->mnt_hash, tree_list);
 199                 } else {
 200                         /*
 201                          * This can happen if the parent mount was bind mounted
 202                          * on some subdirectory of a shared/slave mount.
 203                          */
 204                         list_add_tail(&child->mnt_hash, &tmp_list);
 205                 }
 206                 prev_dest_mnt = m;
 207                 prev_src_mnt  = child;
 208         }
 209 out:
 210         spin_lock(&vfsmount_lock);
 211         while (!list_empty(&tmp_list)) {
 212                 child = list_entry(tmp_list.next, struct vfsmount, mnt_hash);
 213                 list_del_init(&child->mnt_hash);
 214                 umount_tree(child, 0, &umount_list);
 215         }
 216         spin_unlock(&vfsmount_lock);
 217         release_mounts(&umount_list);
 218         return ret;
 219 }
 220
 221 /*
 222  * return true if the refcount is greater than count
 223  */
 224 static inline int do_refcount_check(struct vfsmount *mnt, int count)
 225 {
 226         int mycount = atomic_read(&mnt->mnt_count);
 227         return (mycount > count);
 228 }
 229
 230 /*
 231  * check if the mount 'mnt' can be unmounted successfully.
 232  * @mnt: the mount to be checked for unmount
 233  * NOTE: unmounting 'mnt' would naturally propagate to all
 234  * other mounts its parent propagates to.
 235  * Check if any of these mounts that **do not have submounts**
 236  * have more references than 'refcnt'. If so return busy.
 237  */
 238 int propagate_mount_busy(struct vfsmount *mnt, int refcnt)
 239 {
 240         struct vfsmount *m, *child;
 241         struct vfsmount *parent = mnt->mnt_parent;
 242         int ret = 0;
 243
 244         if (mnt == parent)
 245                 return do_refcount_check(mnt, refcnt);
 246
 247         /*
 248          * quickly check if the current mount can be unmounted.
 249          * If not, we don't have to go checking for all other
 250          * mounts
 251          */
 252         if (!list_empty(&mnt->mnt_mounts) || do_refcount_check(mnt, refcnt))
 253                 return 1;
 254
 255         for (m = propagation_next(parent, parent); m;
 256                         m = propagation_next(m, parent)) {
 257                 child = __lookup_mnt(m, mnt->mnt_mountpoint, 0);
 258                 if (child && list_empty(&child->mnt_mounts) &&
 259                     (ret = do_refcount_check(child, 1)))
 260                         break;
 261         }
 262         return ret;
 263 }
 264
 265 /*
 266  * NOTE: unmounting 'mnt' naturally propagates to all other mounts its
 267  * parent propagates to.
 268  */
 269 static void __propagate_umount(struct vfsmount *mnt)
 270 {
 271         struct vfsmount *parent = mnt->mnt_parent;
 272         struct vfsmount *m;
 273
 274         BUG_ON(parent == mnt);
 275
 276         for (m = propagation_next(parent, parent); m;
 277                         m = propagation_next(m, parent)) {
 278
 279                 struct vfsmount *child = __lookup_mnt(m,
 280                                         mnt->mnt_mountpoint, 0);
 281                 /*
 282                  * umount the child only if the child has no
 283                  * other children
 284                  */
 285                 if (child && list_empty(&child->mnt_mounts))
 286                         list_move_tail(&child->mnt_hash, &mnt->mnt_hash);
 287         }
 288 }
 289
 290 /*
 291  * collect all mounts that receive propagation from the mount in @list,
 292  * and return these additional mounts in the same list.
 293  * @list: the list of mounts to be unmounted.
 294  */
 295 int propagate_umount(struct list_head *list)
 296 {
 297         struct vfsmount *mnt;
 298
 299         list_for_each_entry(mnt, list, mnt_hash)
 300                 __propagate_umount(mnt);
 301         return 0;
 302 }