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/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_del(&mnt->mnt_slave);
  57                 list_add(&mnt->mnt_slave, &master->mnt_slave_list);
  58                 list_splice(&mnt->mnt_slave_list, master->mnt_slave_list.prev);
  59                 INIT_LIST_HEAD(&mnt->mnt_slave_list);
  60         } else {
  61                 struct list_head *p = &mnt->mnt_slave_list;
  62                 while (!list_empty(p)) {
  63                         slave_mnt = list_entry(p->next,
  64                                         struct vfsmount, mnt_slave);
  65                         list_del_init(&slave_mnt->mnt_slave);
  66                         slave_mnt->mnt_master = NULL;
  67                 }
  68         }
  69         mnt->mnt_master = master;
  70         CLEAR_MNT_SHARED(mnt);
  71         INIT_LIST_HEAD(&mnt->mnt_slave_list);
  72         return 0;
  73 }
  74
  75 void change_mnt_propagation(struct vfsmount *mnt, int type)
  76 {
  77         if (type == MS_SHARED) {
  78                 set_mnt_shared(mnt);
  79                 return;
  80         }
  81         do_make_slave(mnt);
  82         if (type != MS_SLAVE) {
  83                 list_del_init(&mnt->mnt_slave);
  84                 mnt->mnt_master = NULL;
  85                 if (type == MS_UNBINDABLE)
  86                         mnt->mnt_flags |= MNT_UNBINDABLE;
  87         }
  88 }
  89
  90 /*
  91  * get the next mount in the propagation tree.
  92  * @m: the mount seen last
  93  * @origin: the original mount from where the tree walk initiated
  94  */
  95 static struct vfsmount *propagation_next(struct vfsmount *m,
  96                                          struct vfsmount *origin)
  97 {
  98         /* are there any slaves of this mount? */
  99         if (!IS_MNT_NEW(m) && !list_empty(&m->mnt_slave_list))
 100                 return first_slave(m);
 101
 102         while (1) {
 103                 struct vfsmount *next;
 104                 struct vfsmount *master = m->mnt_master;
 105
 106                 if ( master == origin->mnt_master ) {
 107                         next = next_peer(m);
 108                         return ((next == origin) ? NULL : next);
 109                 } else if (m->mnt_slave.next != &master->mnt_slave_list)
 110                         return next_slave(m);
 111
 112                 /* back at master */
 113                 m = master;
 114         }
 115 }
 116
 117 /*
 118  * return the source mount to be used for cloning
 119  *
 120  * @dest        the current destination mount
 121  * @last_dest   the last seen destination mount
 122  * @last_src    the last seen source mount
 123  * @type        return CL_SLAVE if the new mount has to be
 124  *              cloned as a slave.
 125  */
 126 static struct vfsmount *get_source(struct vfsmount *dest,
 127                                         struct vfsmount *last_dest,
 128                                         struct vfsmount *last_src,
 129                                         int *type)
 130 {
 131         struct vfsmount *p_last_src = NULL;
 132         struct vfsmount *p_last_dest = NULL;
 133         *type = CL_PROPAGATION;;
 134
 135         if (IS_MNT_SHARED(dest))
 136                 *type |= CL_MAKE_SHARED;
 137
 138         while (last_dest != dest->mnt_master) {
 139                 p_last_dest = last_dest;
 140                 p_last_src = last_src;
 141                 last_dest = last_dest->mnt_master;
 142                 last_src = last_src->mnt_master;
 143         }
 144
 145         if (p_last_dest) {
 146                 do {
 147                         p_last_dest = next_peer(p_last_dest);
 148                 } while (IS_MNT_NEW(p_last_dest));
 149         }
 150
 151         if (dest != p_last_dest) {
 152                 *type |= CL_SLAVE;
 153                 return last_src;
 154         } else
 155                 return p_last_src;
 156 }
 157
 158 /*
 159  * mount 'source_mnt' under the destination 'dest_mnt' at
 160  * dentry 'dest_dentry'. And propagate that mount to
 161  * all the peer and slave mounts of 'dest_mnt'.
 162  * Link all the new mounts into a propagation tree headed at
 163  * source_mnt. Also link all the new mounts using ->mnt_list
 164  * headed at source_mnt's ->mnt_list
 165  *
 166  * @dest_mnt: destination mount.
 167  * @dest_dentry: destination dentry.
 168  * @source_mnt: source mount.
 169  * @tree_list : list of heads of trees to be attached.
 170  */
 171 int propagate_mnt(struct vfsmount *dest_mnt, struct dentry *dest_dentry,
 172                     struct vfsmount *source_mnt, struct list_head *tree_list)
 173 {
 174         struct vfsmount *m, *child;
 175         int ret = 0;
 176         struct vfsmount *prev_dest_mnt = dest_mnt;
 177         struct vfsmount *prev_src_mnt  = source_mnt;
 178         LIST_HEAD(tmp_list);
 179         LIST_HEAD(umount_list);
 180
 181         for (m = propagation_next(dest_mnt, dest_mnt); m;
 182                         m = propagation_next(m, dest_mnt)) {
 183                 int type;
 184                 struct vfsmount *source;
 185
 186                 if (IS_MNT_NEW(m))
 187                         continue;
 188
 189                 source =  get_source(m, prev_dest_mnt, prev_src_mnt, &type);
 190
 191                 if (!(child = copy_tree(source, source->mnt_root, type))) {
 192                         ret = -ENOMEM;
 193                         list_splice(tree_list, tmp_list.prev);
 194                         goto out;
 195                 }
 196
 197                 if (is_subdir(dest_dentry, m->mnt_root)) {
 198                         mnt_set_mountpoint(m, dest_dentry, child);
 199                         list_add_tail(&child->mnt_hash, tree_list);
 200                 } else {
 201                         /*
 202                          * This can happen if the parent mount was bind mounted
 203                          * on some subdirectory of a shared/slave mount.
 204                          */
 205                         list_add_tail(&child->mnt_hash, &tmp_list);
 206                 }
 207                 prev_dest_mnt = m;
 208                 prev_src_mnt  = child;
 209         }
 210 out:
 211         spin_lock(&vfsmount_lock);
 212         while (!list_empty(&tmp_list)) {
 213                 child = list_entry(tmp_list.next, struct vfsmount, mnt_hash);
 214                 list_del_init(&child->mnt_hash);
 215                 umount_tree(child, 0, &umount_list);
 216         }
 217         spin_unlock(&vfsmount_lock);
 218         release_mounts(&umount_list);
 219         return ret;
 220 }
 221
 222 /*
 223  * return true if the refcount is greater than count
 224  */
 225 static inline int do_refcount_check(struct vfsmount *mnt, int count)
 226 {
 227         int mycount = atomic_read(&mnt->mnt_count);
 228         return (mycount > count);
 229 }
 230
 231 /*
 232  * check if the mount 'mnt' can be unmounted successfully.
 233  * @mnt: the mount to be checked for unmount
 234  * NOTE: unmounting 'mnt' would naturally propagate to all
 235  * other mounts its parent propagates to.
 236  * Check if any of these mounts that **do not have submounts**
 237  * have more references than 'refcnt'. If so return busy.
 238  */
 239 int propagate_mount_busy(struct vfsmount *mnt, int refcnt)
 240 {
 241         struct vfsmount *m, *child;
 242         struct vfsmount *parent = mnt->mnt_parent;
 243         int ret = 0;
 244
 245         if (mnt == parent)
 246                 return do_refcount_check(mnt, refcnt);
 247
 248         /*
 249          * quickly check if the current mount can be unmounted.
 250          * If not, we don't have to go checking for all other
 251          * mounts
 252          */
 253         if (!list_empty(&mnt->mnt_mounts) || do_refcount_check(mnt, refcnt))
 254                 return 1;
 255
 256         for (m = propagation_next(parent, parent); m;
 257                         m = propagation_next(m, parent)) {
 258                 child = __lookup_mnt(m, mnt->mnt_mountpoint, 0);
 259                 if (child && list_empty(&child->mnt_mounts) &&
 260                     (ret = do_refcount_check(child, 1)))
 261                         break;
 262         }
 263         return ret;
 264 }
 265
 266 /*
 267  * NOTE: unmounting 'mnt' naturally propagates to all other mounts its
 268  * parent propagates to.
 269  */
 270 static void __propagate_umount(struct vfsmount *mnt)
 271 {
 272         struct vfsmount *parent = mnt->mnt_parent;
 273         struct vfsmount *m;
 274
 275         BUG_ON(parent == mnt);
 276
 277         for (m = propagation_next(parent, parent); m;
 278                         m = propagation_next(m, parent)) {
 279
 280                 struct vfsmount *child = __lookup_mnt(m,
 281                                         mnt->mnt_mountpoint, 0);
 282                 /*
 283                  * umount the child only if the child has no
 284                  * other children
 285                  */
 286                 if (child && list_empty(&child->mnt_mounts)) {
 287                         list_del(&child->mnt_hash);
 288                         list_add_tail(&child->mnt_hash, &mnt->mnt_hash);
 289                 }
 290         }
 291 }
 292
 293 /*
 294  * collect all mounts that receive propagation from the mount in @list,
 295  * and return these additional mounts in the same list.
 296  * @list: the list of mounts to be unmounted.
 297  */
 298 int propagate_umount(struct list_head *list)
 299 {
 300         struct vfsmount *mnt;
 301
 302         list_for_each_entry(mnt, list, mnt_hash)
 303                 __propagate_umount(mnt);
 304         return 0;
 305 }