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_first_entry(p,
  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                 else
  87                         mnt->mnt_flags &= ~MNT_UNBINDABLE;
  88         }
  89 }
  90
  91 /*
  92  * get the next mount in the propagation tree.
  93  * @m: the mount seen last
  94  * @origin: the original mount from where the tree walk initiated
  95  */
  96 static struct vfsmount *propagation_next(struct vfsmount *m,
  97                                          struct vfsmount *origin)
  98 {
  99         /* are there any slaves of this mount? */
 100         if (!IS_MNT_NEW(m) && !list_empty(&m->mnt_slave_list))
 101                 return first_slave(m);
 102
 103         while (1) {
 104                 struct vfsmount *next;
 105                 struct vfsmount *master = m->mnt_master;
 106
 107                 if (master == origin->mnt_master) {
 108                         next = next_peer(m);
 109                         return ((next == origin) ? NULL : next);
 110                 } else if (m->mnt_slave.next != &master->mnt_slave_list)
 111                         return next_slave(m);
 112
 113                 /* back at master */
 114                 m = master;
 115         }
 116 }
 117
 118 /*
 119  * return the source mount to be used for cloning
 120  *
 121  * @dest        the current destination mount
 122  * @last_dest   the last seen destination mount
 123  * @last_src    the last seen source mount
 124  * @type        return CL_SLAVE if the new mount has to be
 125  *              cloned as a slave.
 126  */
 127 static struct vfsmount *get_source(struct vfsmount *dest,
 128                                         struct vfsmount *last_dest,
 129                                         struct vfsmount *last_src,
 130                                         int *type)
 131 {
 132         struct vfsmount *p_last_src = NULL;
 133         struct vfsmount *p_last_dest = NULL;
 134         *type = CL_PROPAGATION;
 135
 136         if (IS_MNT_SHARED(dest))
 137                 *type |= CL_MAKE_SHARED;
 138
 139         while (last_dest != dest->mnt_master) {
 140                 p_last_dest = last_dest;
 141                 p_last_src = last_src;
 142                 last_dest = last_dest->mnt_master;
 143                 last_src = last_src->mnt_master;
 144         }
 145
 146         if (p_last_dest) {
 147                 do {
 148                         p_last_dest = next_peer(p_last_dest);
 149                 } while (IS_MNT_NEW(p_last_dest));
 150         }
 151
 152         if (dest != p_last_dest) {
 153                 *type |= CL_SLAVE;
 154                 return last_src;
 155         } else
 156                 return p_last_src;
 157 }
 158
 159 /*
 160  * mount 'source_mnt' under the destination 'dest_mnt' at
 161  * dentry 'dest_dentry'. And propagate that mount to
 162  * all the peer and slave mounts of 'dest_mnt'.
 163  * Link all the new mounts into a propagation tree headed at
 164  * source_mnt. Also link all the new mounts using ->mnt_list
 165  * headed at source_mnt's ->mnt_list
 166  *
 167  * @dest_mnt: destination mount.
 168  * @dest_dentry: destination dentry.
 169  * @source_mnt: source mount.
 170  * @tree_list : list of heads of trees to be attached.
 171  */
 172 int propagate_mnt(struct vfsmount *dest_mnt, struct dentry *dest_dentry,
 173                     struct vfsmount *source_mnt, struct list_head *tree_list)
 174 {
 175         struct vfsmount *m, *child;
 176         int ret = 0;
 177         struct vfsmount *prev_dest_mnt = dest_mnt;
 178         struct vfsmount *prev_src_mnt  = source_mnt;
 179         LIST_HEAD(tmp_list);
 180         LIST_HEAD(umount_list);
 181
 182         for (m = propagation_next(dest_mnt, dest_mnt); m;
 183                         m = propagation_next(m, dest_mnt)) {
 184                 int type;
 185                 struct vfsmount *source;
 186
 187                 if (IS_MNT_NEW(m))
 188                         continue;
 189
 190                 source =  get_source(m, prev_dest_mnt, prev_src_mnt, &type);
 191
 192                 if (!(child = copy_tree(source, source->mnt_root, type))) {
 193                         ret = -ENOMEM;
 194                         list_splice(tree_list, tmp_list.prev);
 195                         goto out;
 196                 }
 197
 198                 if (is_subdir(dest_dentry, m->mnt_root)) {
 199                         mnt_set_mountpoint(m, dest_dentry, child);
 200                         list_add_tail(&child->mnt_hash, tree_list);
 201                 } else {
 202                         /*
 203                          * This can happen if the parent mount was bind mounted
 204                          * on some subdirectory of a shared/slave mount.
 205                          */
 206                         list_add_tail(&child->mnt_hash, &tmp_list);
 207                 }
 208                 prev_dest_mnt = m;
 209                 prev_src_mnt  = child;
 210         }
 211 out:
 212         spin_lock(&vfsmount_lock);
 213         while (!list_empty(&tmp_list)) {
 214                 child = list_entry(tmp_list.next, struct vfsmount, mnt_hash);
 215                 list_del_init(&child->mnt_hash);
 216                 umount_tree(child, 0, &umount_list);
 217         }
 218         spin_unlock(&vfsmount_lock);
 219         release_mounts(&umount_list);
 220         return ret;
 221 }
 222
 223 /*
 224  * return true if the refcount is greater than count
 225  */
 226 static inline int do_refcount_check(struct vfsmount *mnt, int count)
 227 {
 228         int mycount = atomic_read(&mnt->mnt_count) - mnt->mnt_ghosts;
 229         return (mycount > count);
 230 }
 231
 232 /*
 233  * check if the mount 'mnt' can be unmounted successfully.
 234  * @mnt: the mount to be checked for unmount
 235  * NOTE: unmounting 'mnt' would naturally propagate to all
 236  * other mounts its parent propagates to.
 237  * Check if any of these mounts that **do not have submounts**
 238  * have more references than 'refcnt'. If so return busy.
 239  */
 240 int propagate_mount_busy(struct vfsmount *mnt, int refcnt)
 241 {
 242         struct vfsmount *m, *child;
 243         struct vfsmount *parent = mnt->mnt_parent;
 244         int ret = 0;
 245
 246         if (mnt == parent)
 247                 return do_refcount_check(mnt, refcnt);
 248
 249         /*
 250          * quickly check if the current mount can be unmounted.
 251          * If not, we don't have to go checking for all other
 252          * mounts
 253          */
 254         if (!list_empty(&mnt->mnt_mounts) || do_refcount_check(mnt, refcnt))
 255                 return 1;
 256
 257         for (m = propagation_next(parent, parent); m;
 258                         m = propagation_next(m, parent)) {
 259                 child = __lookup_mnt(m, mnt->mnt_mountpoint, 0);
 260                 if (child && list_empty(&child->mnt_mounts) &&
 261                     (ret = do_refcount_check(child, 1)))
 262                         break;
 263         }
 264         return ret;
 265 }
 266
 267 /*
 268  * NOTE: unmounting 'mnt' naturally propagates to all other mounts its
 269  * parent propagates to.
 270  */
 271 static void __propagate_umount(struct vfsmount *mnt)
 272 {
 273         struct vfsmount *parent = mnt->mnt_parent;
 274         struct vfsmount *m;
 275
 276         BUG_ON(parent == mnt);
 277
 278         for (m = propagation_next(parent, parent); m;
 279                         m = propagation_next(m, parent)) {
 280
 281                 struct vfsmount *child = __lookup_mnt(m,
 282                                         mnt->mnt_mountpoint, 0);
 283                 /*
 284                  * umount the child only if the child has no
 285                  * other children
 286                  */
 287                 if (child && list_empty(&child->mnt_mounts))
 288                         list_move_tail(&child->mnt_hash, &mnt->mnt_hash);
 289         }
 290 }
 291
 292 /*
 293  * collect all mounts that receive propagation from the mount in @list,
 294  * and return these additional mounts in the same list.
 295  * @list: the list of mounts to be unmounted.
 296  */
 297 int propagate_umount(struct list_head *list)
 298 {
 299         struct vfsmount *mnt;
 300
 301         list_for_each_entry(mnt, list, mnt_hash)
 302                 __propagate_umount(mnt);
 303         return 0;
 304 }