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