4 * (C) Copyright IBM Corporation 2005.
5 * Released under GPL v2.
6 * Author : Ram Pai (linuxram@us.ibm.com)
9 #include <linux/mnt_namespace.h>
10 #include <linux/mount.h>
15 /* return the next shared peer mount of @p */
16 static inline struct vfsmount *next_peer(struct vfsmount *p)
18 return list_entry(p->mnt_share.next, struct vfsmount, mnt_share);
21 static inline struct vfsmount *first_slave(struct vfsmount *p)
23 return list_entry(p->mnt_slave_list.next, struct vfsmount, mnt_slave);
26 static inline struct vfsmount *next_slave(struct vfsmount *p)
28 return list_entry(p->mnt_slave.next, struct vfsmount, mnt_slave);
32 * Return true if path is reachable from root
34 * namespace_sem is held, and mnt is attached
36 static bool is_path_reachable(struct vfsmount *mnt, struct dentry *dentry,
37 const struct path *root)
39 while (mnt != root->mnt && mnt->mnt_parent != mnt) {
40 dentry = mnt->mnt_mountpoint;
41 mnt = mnt->mnt_parent;
43 return mnt == root->mnt && is_subdir(dentry, root->dentry);
46 static struct vfsmount *get_peer_under_root(struct vfsmount *mnt,
47 struct mnt_namespace *ns,
48 const struct path *root)
50 struct vfsmount *m = mnt;
53 /* Check the namespace first for optimization */
54 if (m->mnt_ns == ns && is_path_reachable(m, m->mnt_root, root))
64 * Get ID of closest dominating peer group having a representative
65 * under the given root.
67 * Caller must hold namespace_sem
69 int get_dominating_id(struct vfsmount *mnt, const struct path *root)
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);
76 return d->mnt_group_id;
82 static int do_make_slave(struct vfsmount *mnt)
84 struct vfsmount *peer_mnt = mnt, *master = mnt->mnt_master;
85 struct vfsmount *slave_mnt;
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.
92 while ((peer_mnt = next_peer(peer_mnt)) != mnt &&
93 peer_mnt->mnt_root != mnt->mnt_root) ;
95 if (peer_mnt == mnt) {
96 peer_mnt = next_peer(mnt);
100 if (IS_MNT_SHARED(mnt) && list_empty(&mnt->mnt_share))
101 mnt_release_group_id(mnt);
103 list_del_init(&mnt->mnt_share);
104 mnt->mnt_group_id = 0;
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);
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;
124 mnt->mnt_master = master;
125 CLEAR_MNT_SHARED(mnt);
130 * vfsmount lock must be held for write
132 void change_mnt_propagation(struct vfsmount *mnt, int type)
134 if (type == MS_SHARED) {
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;
145 mnt->mnt_flags &= ~MNT_UNBINDABLE;
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
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.
159 static struct vfsmount *propagation_next(struct vfsmount *m,
160 struct vfsmount *origin)
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);
167 struct vfsmount *next;
168 struct vfsmount *master = m->mnt_master;
170 if (master == origin->mnt_master) {
172 return ((next == origin) ? NULL : next);
173 } else if (m->mnt_slave.next != &master->mnt_slave_list)
174 return next_slave(m);
182 * return the source mount to be used for cloning
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
190 static struct vfsmount *get_source(struct vfsmount *dest,
191 struct vfsmount *last_dest,
192 struct vfsmount *last_src,
195 struct vfsmount *p_last_src = NULL;
196 struct vfsmount *p_last_dest = NULL;
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;
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;
215 /* slave of the earlier, then */
217 /* beginning of peer group among the slaves? */
218 if (IS_MNT_SHARED(dest))
219 *type |= CL_MAKE_SHARED;
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
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.
236 int propagate_mnt(struct vfsmount *dest_mnt, struct dentry *dest_dentry,
237 struct vfsmount *source_mnt, struct list_head *tree_list)
239 struct vfsmount *m, *child;
241 struct vfsmount *prev_dest_mnt = dest_mnt;
242 struct vfsmount *prev_src_mnt = source_mnt;
244 LIST_HEAD(umount_list);
246 for (m = propagation_next(dest_mnt, dest_mnt); m;
247 m = propagation_next(m, dest_mnt)) {
249 struct vfsmount *source;
254 source = get_source(m, prev_dest_mnt, prev_src_mnt, &type);
256 if (!(child = copy_tree(source, source->mnt_root, type))) {
258 list_splice(tree_list, tmp_list.prev);
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);
267 * This can happen if the parent mount was bind mounted
268 * on some subdirectory of a shared/slave mount.
270 list_add_tail(&child->mnt_hash, &tmp_list);
273 prev_src_mnt = child;
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);
281 br_write_unlock(vfsmount_lock);
282 release_mounts(&umount_list);
287 * return true if the refcount is greater than count
289 static inline int do_refcount_check(struct vfsmount *mnt, int count)
291 int mycount = mnt_get_count(mnt) - mnt->mnt_ghosts;
292 return (mycount > count);
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.
303 * vfsmount lock must be held for write
305 int propagate_mount_busy(struct vfsmount *mnt, int refcnt)
307 struct vfsmount *m, *child;
308 struct vfsmount *parent = mnt->mnt_parent;
312 return do_refcount_check(mnt, refcnt);
315 * quickly check if the current mount can be unmounted.
316 * If not, we don't have to go checking for all other
319 if (!list_empty(&mnt->mnt_mounts) || do_refcount_check(mnt, refcnt))
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)))
333 * NOTE: unmounting 'mnt' naturally propagates to all other mounts its
334 * parent propagates to.
336 static void __propagate_umount(struct vfsmount *mnt)
338 struct vfsmount *parent = mnt->mnt_parent;
341 BUG_ON(parent == mnt);
343 for (m = propagation_next(parent, parent); m;
344 m = propagation_next(m, parent)) {
346 struct vfsmount *child = __lookup_mnt(m,
347 mnt->mnt_mountpoint, 0);
349 * umount the child only if the child has no
352 if (child && list_empty(&child->mnt_mounts))
353 list_move_tail(&child->mnt_hash, &mnt->mnt_hash);
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.
362 * vfsmount lock must be held for write
364 int propagate_umount(struct list_head *list)
366 struct vfsmount *mnt;
368 list_for_each_entry(mnt, list, mnt_hash)
369 __propagate_umount(mnt);