/* * linux/fs/pnode.c * * (C) Copyright IBM Corporation 2005. * Released under GPL v2. * Author : Ram Pai (linuxram@us.ibm.com) * */ #include <linux/mnt_namespace.h> #include <linux/mount.h> #include <linux/fs.h> #include "internal.h" #include "pnode.h" /* return the next shared peer mount of @p */ static inline struct vfsmount *next_peer(struct vfsmount *p) { return list_entry(p->mnt_share.next, struct vfsmount, mnt_share); } static inline struct vfsmount *first_slave(struct vfsmount *p) { return list_entry(p->mnt_slave_list.next, struct vfsmount, mnt_slave); } static inline struct vfsmount *next_slave(struct vfsmount *p) { return list_entry(p->mnt_slave.next, struct vfsmount, mnt_slave); } /* * Return true if path is reachable from root * * namespace_sem is held, and mnt is attached */ static bool is_path_reachable(struct vfsmount *mnt, struct dentry *dentry, const struct path *root) { while (mnt != root->mnt && mnt->mnt_parent != mnt) { dentry = mnt->mnt_mountpoint; mnt = mnt->mnt_parent; } return mnt == root->mnt && is_subdir(dentry, root->dentry); } static struct vfsmount *get_peer_under_root(struct vfsmount *mnt, struct mnt_namespace *ns, const struct path *root) { struct vfsmount *m = mnt; do { /* Check the namespace first for optimization */ if (m->mnt_ns == ns && is_path_reachable(m, m->mnt_root, root)) return m; m = next_peer(m); } while (m != mnt); return NULL; } /* * Get ID of closest dominating peer group having a representative * under the given root. * * Caller must hold namespace_sem */ int get_dominating_id(struct vfsmount *mnt, const struct path *root) { struct vfsmount *m; for (m = mnt->mnt_master; m != NULL; m = m->mnt_master) { struct vfsmount *d = get_peer_under_root(m, mnt->mnt_ns, root); if (d) return d->mnt_group_id; } return 0; } static int do_make_slave(struct vfsmount *mnt) { struct vfsmount *peer_mnt = mnt, *master = mnt->mnt_master; struct vfsmount *slave_mnt; /* * slave 'mnt' to a peer mount that has the * same root dentry. If none is available then * slave it to anything that is available. */ while ((peer_mnt = next_peer(peer_mnt)) != mnt && peer_mnt->mnt_root != mnt->mnt_root) ; if (peer_mnt == mnt) { peer_mnt = next_peer(mnt); if (peer_mnt == mnt) peer_mnt = NULL; } if (IS_MNT_SHARED(mnt) && list_empty(&mnt->mnt_share)) mnt_release_group_id(mnt); list_del_init(&mnt->mnt_share); mnt->mnt_group_id = 0; if (peer_mnt) master = peer_mnt; if (master) { list_for_each_entry(slave_mnt, &mnt->mnt_slave_list, mnt_slave) slave_mnt->mnt_master = master; list_move(&mnt->mnt_slave, &master->mnt_slave_list); list_splice(&mnt->mnt_slave_list, master->mnt_slave_list.prev); INIT_LIST_HEAD(&mnt->mnt_slave_list); } else { struct list_head *p = &mnt->mnt_slave_list; while (!list_empty(p)) { slave_mnt = list_first_entry(p, struct vfsmount, mnt_slave); list_del_init(&slave_mnt->mnt_slave); slave_mnt->mnt_master = NULL; } } mnt->mnt_master = master; CLEAR_MNT_SHARED(mnt); return 0; } /* * vfsmount lock must be held for write */ void change_mnt_propagation(struct vfsmount *mnt, int type) { if (type == MS_SHARED) { set_mnt_shared(mnt); return; } do_make_slave(mnt); if (type != MS_SLAVE) { list_del_init(&mnt->mnt_slave); mnt->mnt_master = NULL; if (type == MS_UNBINDABLE) mnt->mnt_flags |= MNT_UNBINDABLE; else mnt->mnt_flags &= ~MNT_UNBINDABLE; } } /* * get the next mount in the propagation tree. * @m: the mount seen last * @origin: the original mount from where the tree walk initiated * * Note that peer groups form contiguous segments of slave lists. * We rely on that in get_source() to be able to find out if * vfsmount found while iterating with propagation_next() is * a peer of one we'd found earlier. */ static struct vfsmount *propagation_next(struct vfsmount *m, struct vfsmount *origin) { /* are there any slaves of this mount? */ if (!IS_MNT_NEW(m) && !list_empty(&m->mnt_slave_list)) return first_slave(m); while (1) { struct vfsmount *next; struct vfsmount *master = m->mnt_master; if (master == origin->mnt_master) { next = next_peer(m); return ((next == origin) ? NULL : next); } else if (m->mnt_slave.next != &master->mnt_slave_list) return next_slave(m); /* back at master */ m = master; } } /* * return the source mount to be used for cloning * * @dest the current destination mount * @last_dest the last seen destination mount * @last_src the last seen source mount * @type return CL_SLAVE if the new mount has to be * cloned as a slave. */ static struct vfsmount *get_source(struct vfsmount *dest, struct vfsmount *last_dest, struct vfsmount *last_src, int *type) { struct vfsmount *p_last_src = NULL; struct vfsmount *p_last_dest = NULL; while (last_dest != dest->mnt_master) { p_last_dest = last_dest; p_last_src = last_src; last_dest = last_dest->mnt_master; last_src = last_src->mnt_master; } if (p_last_dest) { do { p_last_dest = next_peer(p_last_dest); } while (IS_MNT_NEW(p_last_dest)); /* is that a peer of the earlier? */ if (dest == p_last_dest) { *type = CL_MAKE_SHARED; return p_last_src; } } /* slave of the earlier, then */ *type = CL_SLAVE; /* beginning of peer group among the slaves? */ if (IS_MNT_SHARED(dest)) *type |= CL_MAKE_SHARED; return last_src; } /* * mount 'source_mnt' under the destination 'dest_mnt' at * dentry 'dest_dentry'. And propagate that mount to * all the peer and slave mounts of 'dest_mnt'. * Link all the new mounts into a propagation tree headed at * source_mnt. Also link all the new mounts using ->mnt_list * headed at source_mnt's ->mnt_list * * @dest_mnt: destination mount. * @dest_dentry: destination dentry. * @source_mnt: source mount. * @tree_list : list of heads of trees to be attached. */ int propagate_mnt(struct vfsmount *dest_mnt, struct dentry *dest_dentry, struct vfsmount *source_mnt, struct list_head *tree_list) { struct vfsmount *m, *child; int ret = 0; struct vfsmount *prev_dest_mnt = dest_mnt; struct vfsmount *prev_src_mnt = source_mnt; LIST_HEAD(tmp_list); LIST_HEAD(umount_list); for (m = propagation_next(dest_mnt, dest_mnt); m; m = propagation_next(m, dest_mnt)) { int type; struct vfsmount *source; if (IS_MNT_NEW(m)) continue; source = get_source(m, prev_dest_mnt, prev_src_mnt, &type); if (!(child = copy_tree(source, source->mnt_root, type))) { ret = -ENOMEM; list_splice(tree_list, tmp_list.prev); goto out; } if (is_subdir(dest_dentry, m->mnt_root)) { mnt_set_mountpoint(m, dest_dentry, child); list_add_tail(&child->mnt_hash, tree_list); } else { /* * This can happen if the parent mount was bind mounted * on some subdirectory of a shared/slave mount. */ list_add_tail(&child->mnt_hash, &tmp_list); } prev_dest_mnt = m; prev_src_mnt = child; } out: br_write_lock(vfsmount_lock); while (!list_empty(&tmp_list)) { child = list_first_entry(&tmp_list, struct vfsmount, mnt_hash); umount_tree(child, 0, &umount_list); } br_write_unlock(vfsmount_lock); release_mounts(&umount_list); return ret; } /* * return true if the refcount is greater than count */ static inline int do_refcount_check(struct vfsmount *mnt, int count) { int mycount = mnt_get_count(mnt) - mnt->mnt_ghosts; return (mycount > count); } /* * check if the mount 'mnt' can be unmounted successfully. * @mnt: the mount to be checked for unmount * NOTE: unmounting 'mnt' would naturally propagate to all * other mounts its parent propagates to. * Check if any of these mounts that **do not have submounts** * have more references than 'refcnt'. If so return busy. * * vfsmount lock must be held for write */ int propagate_mount_busy(struct vfsmount *mnt, int refcnt) { struct vfsmount *m, *child; struct vfsmount *parent = mnt->mnt_parent; int ret = 0; if (mnt == parent) return do_refcount_check(mnt, refcnt); /* * quickly check if the current mount can be unmounted. * If not, we don't have to go checking for all other * mounts */ if (!list_empty(&mnt->mnt_mounts) || do_refcount_check(mnt, refcnt)) return 1; for (m = propagation_next(parent, parent); m; m = propagation_next(m, parent)) { child = __lookup_mnt(m, mnt->mnt_mountpoint, 0); if (child && list_empty(&child->mnt_mounts) && (ret = do_refcount_check(child, 1))) break; } return ret; } /* * NOTE: unmounting 'mnt' naturally propagates to all other mounts its * parent propagates to. */ static void __propagate_umount(struct vfsmount *mnt) { struct vfsmount *parent = mnt->mnt_parent; struct vfsmount *m; BUG_ON(parent == mnt); for (m = propagation_next(parent, parent); m; m = propagation_next(m, parent)) { struct vfsmount *child = __lookup_mnt(m, mnt->mnt_mountpoint, 0); /* * umount the child only if the child has no * other children */ if (child && list_empty(&child->mnt_mounts)) list_move_tail(&child->mnt_hash, &mnt->mnt_hash); } } /* * collect all mounts that receive propagation from the mount in @list, * and return these additional mounts in the same list. * @list: the list of mounts to be unmounted. * * vfsmount lock must be held for write */ int propagate_umount(struct list_head *list) { struct vfsmount *mnt; list_for_each_entry(mnt, list, mnt_hash) __propagate_umount(mnt); return 0; }