linux/fs/pnode.c
<<
>>
Prefs
   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 vfsmount *next_peer(struct vfsmount *p)
  17{
  18        return list_entry(p->mnt_share.next, struct vfsmount, mnt_share);
  19}
  20
  21static inline struct vfsmount *first_slave(struct vfsmount *p)
  22{
  23        return list_entry(p->mnt_slave_list.next, struct vfsmount, mnt_slave);
  24}
  25
  26static inline struct vfsmount *next_slave(struct vfsmount *p)
  27{
  28        return list_entry(p->mnt_slave.next, struct vfsmount, mnt_slave);
  29}
  30
  31/*
  32 * Return true if path is reachable from root
  33 *
  34 * namespace_sem is held, and mnt is attached
  35 */
  36static bool is_path_reachable(struct vfsmount *mnt, struct dentry *dentry,
  37                         const struct path *root)
  38{
  39        while (mnt != root->mnt && mnt->mnt_parent != mnt) {
  40                dentry = mnt->mnt_mountpoint;
  41                mnt = mnt->mnt_parent;
  42        }
  43        return mnt == root->mnt && is_subdir(dentry, root->dentry);
  44}
  45
  46static struct vfsmount *get_peer_under_root(struct vfsmount *mnt,
  47                                            struct mnt_namespace *ns,
  48                                            const struct path *root)
  49{
  50        struct vfsmount *m = mnt;
  51
  52        do {
  53                /* Check the namespace first for optimization */
  54                if (m->mnt_ns == ns && is_path_reachable(m, m->mnt_root, root))
  55                        return m;
  56
  57                m = next_peer(m);
  58        } while (m != mnt);
  59
  60        return NULL;
  61}
  62
  63/*
  64 * Get ID of closest dominating peer group having a representative
  65 * under the given root.
  66 *
  67 * Caller must hold namespace_sem
  68 */
  69int get_dominating_id(struct vfsmount *mnt, const struct path *root)
  70{
  71        struct vfsmount *m;
  72
  73        for (m = mnt->mnt_master; m != NULL; m = m->mnt_master) {
  74                struct vfsmount *d = get_peer_under_root(m, mnt->mnt_ns, root);
  75                if (d)
  76                        return d->mnt_group_id;
  77        }
  78
  79        return 0;
  80}
  81
  82static int do_make_slave(struct vfsmount *mnt)
  83{
  84        struct vfsmount *peer_mnt = mnt, *master = mnt->mnt_master;
  85        struct vfsmount *slave_mnt;
  86
  87        /*
  88         * slave 'mnt' to a peer mount that has the
  89         * same root dentry. If none is available then
  90         * slave it to anything that is available.
  91         */
  92        while ((peer_mnt = next_peer(peer_mnt)) != mnt &&
  93               peer_mnt->mnt_root != mnt->mnt_root) ;
  94
  95        if (peer_mnt == mnt) {
  96                peer_mnt = next_peer(mnt);
  97                if (peer_mnt == mnt)
  98                        peer_mnt = NULL;
  99        }
 100        if (IS_MNT_SHARED(mnt) && list_empty(&mnt->mnt_share))
 101                mnt_release_group_id(mnt);
 102
 103        list_del_init(&mnt->mnt_share);
 104        mnt->mnt_group_id = 0;
 105
 106        if (peer_mnt)
 107                master = peer_mnt;
 108
 109        if (master) {
 110                list_for_each_entry(slave_mnt, &mnt->mnt_slave_list, mnt_slave)
 111                        slave_mnt->mnt_master = master;
 112                list_move(&mnt->mnt_slave, &master->mnt_slave_list);
 113                list_splice(&mnt->mnt_slave_list, master->mnt_slave_list.prev);
 114                INIT_LIST_HEAD(&mnt->mnt_slave_list);
 115        } else {
 116                struct list_head *p = &mnt->mnt_slave_list;
 117                while (!list_empty(p)) {
 118                        slave_mnt = list_first_entry(p,
 119                                        struct vfsmount, mnt_slave);
 120                        list_del_init(&slave_mnt->mnt_slave);
 121                        slave_mnt->mnt_master = NULL;
 122                }
 123        }
 124        mnt->mnt_master = master;
 125        CLEAR_MNT_SHARED(mnt);
 126        return 0;
 127}
 128
 129/*
 130 * vfsmount lock must be held for write
 131 */
 132void change_mnt_propagation(struct vfsmount *mnt, int type)
 133{
 134        if (type == MS_SHARED) {
 135                set_mnt_shared(mnt);
 136                return;
 137        }
 138        do_make_slave(mnt);
 139        if (type != MS_SLAVE) {
 140                list_del_init(&mnt->mnt_slave);
 141                mnt->mnt_master = NULL;
 142                if (type == MS_UNBINDABLE)
 143                        mnt->mnt_flags |= MNT_UNBINDABLE;
 144                else
 145                        mnt->mnt_flags &= ~MNT_UNBINDABLE;
 146        }
 147}
 148
 149/*
 150 * get the next mount in the propagation tree.
 151 * @m: the mount seen last
 152 * @origin: the original mount from where the tree walk initiated
 153 *
 154 * Note that peer groups form contiguous segments of slave lists.
 155 * We rely on that in get_source() to be able to find out if
 156 * vfsmount found while iterating with propagation_next() is
 157 * a peer of one we'd found earlier.
 158 */
 159static struct vfsmount *propagation_next(struct vfsmount *m,
 160                                         struct vfsmount *origin)
 161{
 162        /* are there any slaves of this mount? */
 163        if (!IS_MNT_NEW(m) && !list_empty(&m->mnt_slave_list))
 164                return first_slave(m);
 165
 166        while (1) {
 167                struct vfsmount *next;
 168                struct vfsmount *master = m->mnt_master;
 169
 170                if (master == origin->mnt_master) {
 171                        next = next_peer(m);
 172                        return ((next == origin) ? NULL : next);
 173                } else if (m->mnt_slave.next != &master->mnt_slave_list)
 174                        return next_slave(m);
 175
 176                /* back at master */
 177                m = master;
 178        }
 179}
 180
 181/*
 182 * return the source mount to be used for cloning
 183 *
 184 * @dest        the current destination mount
 185 * @last_dest   the last seen destination mount
 186 * @last_src    the last seen source mount
 187 * @type        return CL_SLAVE if the new mount has to be
 188 *              cloned as a slave.
 189 */
 190static struct vfsmount *get_source(struct vfsmount *dest,
 191                                        struct vfsmount *last_dest,
 192                                        struct vfsmount *last_src,
 193                                        int *type)
 194{
 195        struct vfsmount *p_last_src = NULL;
 196        struct vfsmount *p_last_dest = NULL;
 197
 198        while (last_dest != dest->mnt_master) {
 199                p_last_dest = last_dest;
 200                p_last_src = last_src;
 201                last_dest = last_dest->mnt_master;
 202                last_src = last_src->mnt_master;
 203        }
 204
 205        if (p_last_dest) {
 206                do {
 207                        p_last_dest = next_peer(p_last_dest);
 208                } while (IS_MNT_NEW(p_last_dest));
 209                /* is that a peer of the earlier? */
 210                if (dest == p_last_dest) {
 211                        *type = CL_MAKE_SHARED;
 212                        return p_last_src;
 213                }
 214        }
 215        /* slave of the earlier, then */
 216        *type = CL_SLAVE;
 217        /* beginning of peer group among the slaves? */
 218        if (IS_MNT_SHARED(dest))
 219                *type |= CL_MAKE_SHARED;
 220        return last_src;
 221}
 222
 223/*
 224 * mount 'source_mnt' under the destination 'dest_mnt' at
 225 * dentry 'dest_dentry'. And propagate that mount to
 226 * all the peer and slave mounts of 'dest_mnt'.
 227 * Link all the new mounts into a propagation tree headed at
 228 * source_mnt. Also link all the new mounts using ->mnt_list
 229 * headed at source_mnt's ->mnt_list
 230 *
 231 * @dest_mnt: destination mount.
 232 * @dest_dentry: destination dentry.
 233 * @source_mnt: source mount.
 234 * @tree_list : list of heads of trees to be attached.
 235 */
 236int propagate_mnt(struct vfsmount *dest_mnt, struct dentry *dest_dentry,
 237                    struct vfsmount *source_mnt, struct list_head *tree_list)
 238{
 239        struct vfsmount *m, *child;
 240        int ret = 0;
 241        struct vfsmount *prev_dest_mnt = dest_mnt;
 242        struct vfsmount *prev_src_mnt  = source_mnt;
 243        LIST_HEAD(tmp_list);
 244        LIST_HEAD(umount_list);
 245
 246        for (m = propagation_next(dest_mnt, dest_mnt); m;
 247                        m = propagation_next(m, dest_mnt)) {
 248                int type;
 249                struct vfsmount *source;
 250
 251                if (IS_MNT_NEW(m))
 252                        continue;
 253
 254                source =  get_source(m, prev_dest_mnt, prev_src_mnt, &type);
 255
 256                if (!(child = copy_tree(source, source->mnt_root, type))) {
 257                        ret = -ENOMEM;
 258                        list_splice(tree_list, tmp_list.prev);
 259                        goto out;
 260                }
 261
 262                if (is_subdir(dest_dentry, m->mnt_root)) {
 263                        mnt_set_mountpoint(m, dest_dentry, child);
 264                        list_add_tail(&child->mnt_hash, tree_list);
 265                } else {
 266                        /*
 267                         * This can happen if the parent mount was bind mounted
 268                         * on some subdirectory of a shared/slave mount.
 269                         */
 270                        list_add_tail(&child->mnt_hash, &tmp_list);
 271                }
 272                prev_dest_mnt = m;
 273                prev_src_mnt  = child;
 274        }
 275out:
 276        br_write_lock(vfsmount_lock);
 277        while (!list_empty(&tmp_list)) {
 278                child = list_first_entry(&tmp_list, struct vfsmount, mnt_hash);
 279                umount_tree(child, 0, &umount_list);
 280        }
 281        br_write_unlock(vfsmount_lock);
 282        release_mounts(&umount_list);
 283        return ret;
 284}
 285
 286/*
 287 * return true if the refcount is greater than count
 288 */
 289static inline int do_refcount_check(struct vfsmount *mnt, int count)
 290{
 291        int mycount = mnt_get_count(mnt) - mnt->mnt_ghosts;
 292        return (mycount > count);
 293}
 294
 295/*
 296 * check if the mount 'mnt' can be unmounted successfully.
 297 * @mnt: the mount to be checked for unmount
 298 * NOTE: unmounting 'mnt' would naturally propagate to all
 299 * other mounts its parent propagates to.
 300 * Check if any of these mounts that **do not have submounts**
 301 * have more references than 'refcnt'. If so return busy.
 302 *
 303 * vfsmount lock must be held for write
 304 */
 305int propagate_mount_busy(struct vfsmount *mnt, int refcnt)
 306{
 307        struct vfsmount *m, *child;
 308        struct vfsmount *parent = mnt->mnt_parent;
 309        int ret = 0;
 310
 311        if (mnt == parent)
 312                return do_refcount_check(mnt, refcnt);
 313
 314        /*
 315         * quickly check if the current mount can be unmounted.
 316         * If not, we don't have to go checking for all other
 317         * mounts
 318         */
 319        if (!list_empty(&mnt->mnt_mounts) || do_refcount_check(mnt, refcnt))
 320                return 1;
 321
 322        for (m = propagation_next(parent, parent); m;
 323                        m = propagation_next(m, parent)) {
 324                child = __lookup_mnt(m, mnt->mnt_mountpoint, 0);
 325                if (child && list_empty(&child->mnt_mounts) &&
 326                    (ret = do_refcount_check(child, 1)))
 327                        break;
 328        }
 329        return ret;
 330}
 331
 332/*
 333 * NOTE: unmounting 'mnt' naturally propagates to all other mounts its
 334 * parent propagates to.
 335 */
 336static void __propagate_umount(struct vfsmount *mnt)
 337{
 338        struct vfsmount *parent = mnt->mnt_parent;
 339        struct vfsmount *m;
 340
 341        BUG_ON(parent == mnt);
 342
 343        for (m = propagation_next(parent, parent); m;
 344                        m = propagation_next(m, parent)) {
 345
 346                struct vfsmount *child = __lookup_mnt(m,
 347                                        mnt->mnt_mountpoint, 0);
 348                /*
 349                 * umount the child only if the child has no
 350                 * other children
 351                 */
 352                if (child && list_empty(&child->mnt_mounts))
 353                        list_move_tail(&child->mnt_hash, &mnt->mnt_hash);
 354        }
 355}
 356
 357/*
 358 * collect all mounts that receive propagation from the mount in @list,
 359 * and return these additional mounts in the same list.
 360 * @list: the list of mounts to be unmounted.
 361 *
 362 * vfsmount lock must be held for write
 363 */
 364int propagate_umount(struct list_head *list)
 365{
 366        struct vfsmount *mnt;
 367
 368        list_for_each_entry(mnt, list, mnt_hash)
 369                __propagate_umount(mnt);
 370        return 0;
 371}
 372
lxr.linux.no kindly hosted by Redpill Linpro AS, provider of Linux consulting and operations services since 1995.