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 static int do_make_slave(struct vfsmount *mnt)
  32 {
  33         struct vfsmount *peer_mnt = mnt, *master = mnt->mnt_master;
  34         struct vfsmount *slave_mnt;
  35
  36         /*
  37          * slave 'mnt' to a peer mount that has the
  38          * same root dentry. If none is available than
  39          * slave it to anything that is available.
  40          */
  41         while ((peer_mnt = next_peer(peer_mnt)) != mnt &&
  42                peer_mnt->mnt_root != mnt->mnt_root) ;
  43
  44         if (peer_mnt == mnt) {
  45                 peer_mnt = next_peer(mnt);
  46                 if (peer_mnt == mnt)
  47                         peer_mnt = NULL;
  48         }
  49         if (IS_MNT_SHARED(mnt) && list_empty(&mnt->mnt_share))
  50                 mnt_release_group_id(mnt);
  51
  52         list_del_init(&mnt->mnt_share);
  53         mnt->mnt_group_id = 0;
  54
  55         if (peer_mnt)
  56                 master = peer_mnt;
  57
  58         if (master) {
  59                 list_for_each_entry(slave_mnt, &mnt->mnt_slave_list, mnt_slave)
  60                         slave_mnt->mnt_master = master;
  61                 list_move(&mnt->mnt_slave, &master->mnt_slave_list);
  62                 list_splice(&mnt->mnt_slave_list, master->mnt_slave_list.prev);
  63                 INIT_LIST_HEAD(&mnt->mnt_slave_list);
  64         } else {
  65                 struct list_head *p = &mnt->mnt_slave_list;
  66                 while (!list_empty(p)) {
  67                         slave_mnt = list_first_entry(p,
  68                                         struct vfsmount, mnt_slave);
  69                         list_del_init(&slave_mnt->mnt_slave);
  70                         slave_mnt->mnt_master = NULL;
  71                 }
  72         }
  73         mnt->mnt_master = master;
  74         CLEAR_MNT_SHARED(mnt);
  75         return 0;
  76 }
  77
  78 void change_mnt_propagation(struct vfsmount *mnt, int type)
  79 {
  80         if (type == MS_SHARED) {
  81                 set_mnt_shared(mnt);
  82                 return;
  83         }
  84         do_make_slave(mnt);
  85         if (type != MS_SLAVE) {
  86                 list_del_init(&mnt->mnt_slave);
  87                 mnt->mnt_master = NULL;
  88                 if (type == MS_UNBINDABLE)
  89                         mnt->mnt_flags |= MNT_UNBINDABLE;
  90                 else
  91                         mnt->mnt_flags &= ~MNT_UNBINDABLE;
  92         }
  93 }
  94
  95 /*
  96  * get the next mount in the propagation tree.
  97  * @m: the mount seen last
  98  * @origin: the original mount from where the tree walk initiated
  99  */
 100 static struct vfsmount *propagation_next(struct vfsmount *m,
 101                                          struct vfsmount *origin)
 102 {
 103         /* are there any slaves of this mount? */
 104         if (!IS_MNT_NEW(m) && !list_empty(&m->mnt_slave_list))
 105                 return first_slave(m);
 106
 107         while (1) {
 108                 struct vfsmount *next;
 109                 struct vfsmount *master = m->mnt_master;
 110
 111                 if (master == origin->mnt_master) {
 112                         next = next_peer(m);
 113                         return ((next == origin) ? NULL : next);
 114                 } else if (m->mnt_slave.next != &master->mnt_slave_list)
 115                         return next_slave(m);
 116
 117                 /* back at master */
 118                 m = master;
 119         }
 120 }
 121
 122 /*
 123  * return the source mount to be used for cloning
 124  *
 125  * @dest        the current destination mount
 126  * @last_dest   the last seen destination mount
 127  * @last_src    the last seen source mount
 128  * @type        return CL_SLAVE if the new mount has to be
 129  *              cloned as a slave.
 130  */
 131 static struct vfsmount *get_source(struct vfsmount *dest,
 132                                         struct vfsmount *last_dest,
 133                                         struct vfsmount *last_src,
 134                                         int *type)
 135 {
 136         struct vfsmount *p_last_src = NULL;
 137         struct vfsmount *p_last_dest = NULL;
 138         *type = CL_PROPAGATION;
 139
 140         if (IS_MNT_SHARED(dest))
 141                 *type |= CL_MAKE_SHARED;
 142
 143         while (last_dest != dest->mnt_master) {
 144                 p_last_dest = last_dest;
 145                 p_last_src = last_src;
 146                 last_dest = last_dest->mnt_master;
 147                 last_src = last_src->mnt_master;
 148         }
 149
 150         if (p_last_dest) {
 151                 do {
 152                         p_last_dest = next_peer(p_last_dest);
 153                 } while (IS_MNT_NEW(p_last_dest));
 154         }
 155
 156         if (dest != p_last_dest) {
 157                 *type |= CL_SLAVE;
 158                 return last_src;
 159         } else
 160                 return p_last_src;
 161 }
 162
 163 /*
 164  * mount 'source_mnt' under the destination 'dest_mnt' at
 165  * dentry 'dest_dentry'. And propagate that mount to
 166  * all the peer and slave mounts of 'dest_mnt'.
 167  * Link all the new mounts into a propagation tree headed at
 168  * source_mnt. Also link all the new mounts using ->mnt_list
 169  * headed at source_mnt's ->mnt_list
 170  *
 171  * @dest_mnt: destination mount.
 172  * @dest_dentry: destination dentry.
 173  * @source_mnt: source mount.
 174  * @tree_list : list of heads of trees to be attached.
 175  */
 176 int propagate_mnt(struct vfsmount *dest_mnt, struct dentry *dest_dentry,
 177                     struct vfsmount *source_mnt, struct list_head *tree_list)
 178 {
 179         struct vfsmount *m, *child;
 180         int ret = 0;
 181         struct vfsmount *prev_dest_mnt = dest_mnt;
 182         struct vfsmount *prev_src_mnt  = source_mnt;
 183         LIST_HEAD(tmp_list);
 184         LIST_HEAD(umount_list);
 185
 186         for (m = propagation_next(dest_mnt, dest_mnt); m;
 187                         m = propagation_next(m, dest_mnt)) {
 188                 int type;
 189                 struct vfsmount *source;
 190
 191                 if (IS_MNT_NEW(m))
 192                         continue;
 193
 194                 source =  get_source(m, prev_dest_mnt, prev_src_mnt, &type);
 195
 196                 if (!(child = copy_tree(source, source->mnt_root, type))) {
 197                         ret = -ENOMEM;
 198                         list_splice(tree_list, tmp_list.prev);
 199                         goto out;
 200                 }
 201
 202                 if (is_subdir(dest_dentry, m->mnt_root)) {
 203                         mnt_set_mountpoint(m, dest_dentry, child);
 204                         list_add_tail(&child->mnt_hash, tree_list);
 205                 } else {
 206                         /*
 207                          * This can happen if the parent mount was bind mounted
 208                          * on some subdirectory of a shared/slave mount.
 209                          */
 210                         list_add_tail(&child->mnt_hash, &tmp_list);
 211                 }
 212                 prev_dest_mnt = m;
 213                 prev_src_mnt  = child;
 214         }
 215 out:
 216         spin_lock(&vfsmount_lock);
 217         while (!list_empty(&tmp_list)) {
 218                 child = list_first_entry(&tmp_list, struct vfsmount, mnt_hash);
 219                 umount_tree(child, 0, &umount_list);
 220         }
 221         spin_unlock(&vfsmount_lock);
 222         release_mounts(&umount_list);
 223         return ret;
 224 }
 225
 226 /*
 227  * return true if the refcount is greater than count
 228  */
 229 static inline int do_refcount_check(struct vfsmount *mnt, int count)
 230 {
 231         int mycount = atomic_read(&mnt->mnt_count) - mnt->mnt_ghosts;
 232         return (mycount > count);
 233 }
 234
 235 /*
 236  * check if the mount 'mnt' can be unmounted successfully.
 237  * @mnt: the mount to be checked for unmount
 238  * NOTE: unmounting 'mnt' would naturally propagate to all
 239  * other mounts its parent propagates to.
 240  * Check if any of these mounts that **do not have submounts**
 241  * have more references than 'refcnt'. If so return busy.
 242  */
 243 int propagate_mount_busy(struct vfsmount *mnt, int refcnt)
 244 {
 245         struct vfsmount *m, *child;
 246         struct vfsmount *parent = mnt->mnt_parent;
 247         int ret = 0;
 248
 249         if (mnt == parent)
 250                 return do_refcount_check(mnt, refcnt);
 251
 252         /*
 253          * quickly check if the current mount can be unmounted.
 254          * If not, we don't have to go checking for all other
 255          * mounts
 256          */
 257         if (!list_empty(&mnt->mnt_mounts) || do_refcount_check(mnt, refcnt))
 258                 return 1;
 259
 260         for (m = propagation_next(parent, parent); m;
 261                         m = propagation_next(m, parent)) {
 262                 child = __lookup_mnt(m, mnt->mnt_mountpoint, 0);
 263                 if (child && list_empty(&child->mnt_mounts) &&
 264                     (ret = do_refcount_check(child, 1)))
 265                         break;
 266         }
 267         return ret;
 268 }
 269
 270 /*
 271  * NOTE: unmounting 'mnt' naturally propagates to all other mounts its
 272  * parent propagates to.
 273  */
 274 static void __propagate_umount(struct vfsmount *mnt)
 275 {
 276         struct vfsmount *parent = mnt->mnt_parent;
 277         struct vfsmount *m;
 278
 279         BUG_ON(parent == mnt);
 280
 281         for (m = propagation_next(parent, parent); m;
 282                         m = propagation_next(m, parent)) {
 283
 284                 struct vfsmount *child = __lookup_mnt(m,
 285                                         mnt->mnt_mountpoint, 0);
 286                 /*
 287                  * umount the child only if the child has no
 288                  * other children
 289                  */
 290                 if (child && list_empty(&child->mnt_mounts))
 291                         list_move_tail(&child->mnt_hash, &mnt->mnt_hash);
 292         }
 293 }
 294
 295 /*
 296  * collect all mounts that receive propagation from the mount in @list,
 297  * and return these additional mounts in the same list.
 298  * @list: the list of mounts to be unmounted.
 299  */
 300 int propagate_umount(struct list_head *list)
 301 {
 302         struct vfsmount *mnt;
 303
 304         list_for_each_entry(mnt, list, mnt_hash)
 305                 __propagate_umount(mnt);
 306         return 0;
 307 }