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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 <linux/nsproxy.h>
13#include "internal.h"
14#include "pnode.h"
15
16/* return the next shared peer mount of @p */
17static inline struct mount *next_peer(struct mount *p)
18{
19 return list_entry(p->mnt_share.next, struct mount, mnt_share);
20}
21
22static inline struct mount *first_slave(struct mount *p)
23{
24 return list_entry(p->mnt_slave_list.next, struct mount, mnt_slave);
25}
26
27static inline struct mount *next_slave(struct mount *p)
28{
29 return list_entry(p->mnt_slave.next, struct mount, mnt_slave);
30}
31
32static struct mount *get_peer_under_root(struct mount *mnt,
33 struct mnt_namespace *ns,
34 const struct path *root)
35{
36 struct mount *m = mnt;
37
38 do {
39 /* Check the namespace first for optimization */
40 if (m->mnt_ns == ns && is_path_reachable(m, m->mnt.mnt_root, root))
41 return m;
42
43 m = next_peer(m);
44 } while (m != mnt);
45
46 return NULL;
47}
48
49/*
50 * Get ID of closest dominating peer group having a representative
51 * under the given root.
52 *
53 * Caller must hold namespace_sem
54 */
55int get_dominating_id(struct mount *mnt, const struct path *root)
56{
57 struct mount *m;
58
59 for (m = mnt->mnt_master; m != NULL; m = m->mnt_master) {
60 struct mount *d = get_peer_under_root(m, mnt->mnt_ns, root);
61 if (d)
62 return d->mnt_group_id;
63 }
64
65 return 0;
66}
67
68static int do_make_slave(struct mount *mnt)
69{
70 struct mount *peer_mnt = mnt, *master = mnt->mnt_master;
71 struct mount *slave_mnt;
72
73 /*
74 * slave 'mnt' to a peer mount that has the
75 * same root dentry. If none is available then
76 * slave it to anything that is available.
77 */
78 while ((peer_mnt = next_peer(peer_mnt)) != mnt &&
79 peer_mnt->mnt.mnt_root != mnt->mnt.mnt_root) ;
80
81 if (peer_mnt == mnt) {
82 peer_mnt = next_peer(mnt);
83 if (peer_mnt == mnt)
84 peer_mnt = NULL;
85 }
86 if (mnt->mnt_group_id && IS_MNT_SHARED(mnt) &&
87 list_empty(&mnt->mnt_share))
88 mnt_release_group_id(mnt);
89
90 list_del_init(&mnt->mnt_share);
91 mnt->mnt_group_id = 0;
92
93 if (peer_mnt)
94 master = peer_mnt;
95
96 if (master) {
97 list_for_each_entry(slave_mnt, &mnt->mnt_slave_list, mnt_slave)
98 slave_mnt->mnt_master = master;
99 list_move(&mnt->mnt_slave, &master->mnt_slave_list);
100 list_splice(&mnt->mnt_slave_list, master->mnt_slave_list.prev);
101 INIT_LIST_HEAD(&mnt->mnt_slave_list);
102 } else {
103 struct list_head *p = &mnt->mnt_slave_list;
104 while (!list_empty(p)) {
105 slave_mnt = list_first_entry(p,
106 struct mount, mnt_slave);
107 list_del_init(&slave_mnt->mnt_slave);
108 slave_mnt->mnt_master = NULL;
109 }
110 }
111 mnt->mnt_master = master;
112 CLEAR_MNT_SHARED(mnt);
113 return 0;
114}
115
116/*
117 * vfsmount lock must be held for write
118 */
119void change_mnt_propagation(struct mount *mnt, int type)
120{
121 if (type == MS_SHARED) {
122 set_mnt_shared(mnt);
123 return;
124 }
125 do_make_slave(mnt);
126 if (type != MS_SLAVE) {
127 list_del_init(&mnt->mnt_slave);
128 mnt->mnt_master = NULL;
129 if (type == MS_UNBINDABLE)
130 mnt->mnt.mnt_flags |= MNT_UNBINDABLE;
131 else
132 mnt->mnt.mnt_flags &= ~MNT_UNBINDABLE;
133 }
134}
135
136/*
137 * get the next mount in the propagation tree.
138 * @m: the mount seen last
139 * @origin: the original mount from where the tree walk initiated
140 *
141 * Note that peer groups form contiguous segments of slave lists.
142 * We rely on that in get_source() to be able to find out if
143 * vfsmount found while iterating with propagation_next() is
144 * a peer of one we'd found earlier.
145 */
146static struct mount *propagation_next(struct mount *m,
147 struct mount *origin)
148{
149 /* are there any slaves of this mount? */
150 if (!IS_MNT_NEW(m) && !list_empty(&m->mnt_slave_list))
151 return first_slave(m);
152
153 while (1) {
154 struct mount *master = m->mnt_master;
155
156 if (master == origin->mnt_master) {
157 struct mount *next = next_peer(m);
158 return (next == origin) ? NULL : next;
159 } else if (m->mnt_slave.next != &master->mnt_slave_list)
160 return next_slave(m);
161
162 /* back at master */
163 m = master;
164 }
165}
166
167static struct mount *next_group(struct mount *m, struct mount *origin)
168{
169 while (1) {
170 while (1) {
171 struct mount *next;
172 if (!IS_MNT_NEW(m) && !list_empty(&m->mnt_slave_list))
173 return first_slave(m);
174 next = next_peer(m);
175 if (m->mnt_group_id == origin->mnt_group_id) {
176 if (next == origin)
177 return NULL;
178 } else if (m->mnt_slave.next != &next->mnt_slave)
179 break;
180 m = next;
181 }
182 /* m is the last peer */
183 while (1) {
184 struct mount *master = m->mnt_master;
185 if (m->mnt_slave.next != &master->mnt_slave_list)
186 return next_slave(m);
187 m = next_peer(master);
188 if (master->mnt_group_id == origin->mnt_group_id)
189 break;
190 if (master->mnt_slave.next == &m->mnt_slave)
191 break;
192 m = master;
193 }
194 if (m == origin)
195 return NULL;
196 }
197}
198
199/* all accesses are serialized by namespace_sem */
200static struct user_namespace *user_ns;
201static struct mount *last_dest, *first_source, *last_source, *dest_master;
202static struct mountpoint *mp;
203static struct hlist_head *list;
204
205static inline bool peers(struct mount *m1, struct mount *m2)
206{
207 return m1->mnt_group_id == m2->mnt_group_id && m1->mnt_group_id;
208}
209
210static int propagate_one(struct mount *m)
211{
212 struct mount *child;
213 int type;
214 /* skip ones added by this propagate_mnt() */
215 if (IS_MNT_NEW(m))
216 return 0;
217 /* skip if mountpoint isn't covered by it */
218 if (!is_subdir(mp->m_dentry, m->mnt.mnt_root))
219 return 0;
220 if (peers(m, last_dest)) {
221 type = CL_MAKE_SHARED;
222 } else {
223 struct mount *n, *p;
224 bool done;
225 for (n = m; ; n = p) {
226 p = n->mnt_master;
227 if (p == dest_master || IS_MNT_MARKED(p))
228 break;
229 }
230 do {
231 struct mount *parent = last_source->mnt_parent;
232 if (last_source == first_source)
233 break;
234 done = parent->mnt_master == p;
235 if (done && peers(n, parent))
236 break;
237 last_source = last_source->mnt_master;
238 } while (!done);
239
240 type = CL_SLAVE;
241 /* beginning of peer group among the slaves? */
242 if (IS_MNT_SHARED(m))
243 type |= CL_MAKE_SHARED;
244 }
245
246 /* Notice when we are propagating across user namespaces */
247 if (m->mnt_ns->user_ns != user_ns)
248 type |= CL_UNPRIVILEGED;
249 child = copy_tree(last_source, last_source->mnt.mnt_root, type);
250 if (IS_ERR(child))
251 return PTR_ERR(child);
252 child->mnt.mnt_flags &= ~MNT_LOCKED;
253 mnt_set_mountpoint(m, mp, child);
254 last_dest = m;
255 last_source = child;
256 if (m->mnt_master != dest_master) {
257 read_seqlock_excl(&mount_lock);
258 SET_MNT_MARK(m->mnt_master);
259 read_sequnlock_excl(&mount_lock);
260 }
261 hlist_add_head(&child->mnt_hash, list);
262 return 0;
263}
264
265/*
266 * mount 'source_mnt' under the destination 'dest_mnt' at
267 * dentry 'dest_dentry'. And propagate that mount to
268 * all the peer and slave mounts of 'dest_mnt'.
269 * Link all the new mounts into a propagation tree headed at
270 * source_mnt. Also link all the new mounts using ->mnt_list
271 * headed at source_mnt's ->mnt_list
272 *
273 * @dest_mnt: destination mount.
274 * @dest_dentry: destination dentry.
275 * @source_mnt: source mount.
276 * @tree_list : list of heads of trees to be attached.
277 */
278int propagate_mnt(struct mount *dest_mnt, struct mountpoint *dest_mp,
279 struct mount *source_mnt, struct hlist_head *tree_list)
280{
281 struct mount *m, *n;
282 int ret = 0;
283
284 /*
285 * we don't want to bother passing tons of arguments to
286 * propagate_one(); everything is serialized by namespace_sem,
287 * so globals will do just fine.
288 */
289 user_ns = current->nsproxy->mnt_ns->user_ns;
290 last_dest = dest_mnt;
291 first_source = source_mnt;
292 last_source = source_mnt;
293 mp = dest_mp;
294 list = tree_list;
295 dest_master = dest_mnt->mnt_master;
296
297 /* all peers of dest_mnt, except dest_mnt itself */
298 for (n = next_peer(dest_mnt); n != dest_mnt; n = next_peer(n)) {
299 ret = propagate_one(n);
300 if (ret)
301 goto out;
302 }
303
304 /* all slave groups */
305 for (m = next_group(dest_mnt, dest_mnt); m;
306 m = next_group(m, dest_mnt)) {
307 /* everything in that slave group */
308 n = m;
309 do {
310 ret = propagate_one(n);
311 if (ret)
312 goto out;
313 n = next_peer(n);
314 } while (n != m);
315 }
316out:
317 read_seqlock_excl(&mount_lock);
318 hlist_for_each_entry(n, tree_list, mnt_hash) {
319 m = n->mnt_parent;
320 if (m->mnt_master != dest_mnt->mnt_master)
321 CLEAR_MNT_MARK(m->mnt_master);
322 }
323 read_sequnlock_excl(&mount_lock);
324 return ret;
325}
326
327/*
328 * return true if the refcount is greater than count
329 */
330static inline int do_refcount_check(struct mount *mnt, int count)
331{
332 return mnt_get_count(mnt) > count;
333}
334
335/*
336 * check if the mount 'mnt' can be unmounted successfully.
337 * @mnt: the mount to be checked for unmount
338 * NOTE: unmounting 'mnt' would naturally propagate to all
339 * other mounts its parent propagates to.
340 * Check if any of these mounts that **do not have submounts**
341 * have more references than 'refcnt'. If so return busy.
342 *
343 * vfsmount lock must be held for write
344 */
345int propagate_mount_busy(struct mount *mnt, int refcnt)
346{
347 struct mount *m, *child;
348 struct mount *parent = mnt->mnt_parent;
349 int ret = 0;
350
351 if (mnt == parent)
352 return do_refcount_check(mnt, refcnt);
353
354 /*
355 * quickly check if the current mount can be unmounted.
356 * If not, we don't have to go checking for all other
357 * mounts
358 */
359 if (!list_empty(&mnt->mnt_mounts) || do_refcount_check(mnt, refcnt))
360 return 1;
361
362 for (m = propagation_next(parent, parent); m;
363 m = propagation_next(m, parent)) {
364 child = __lookup_mnt_last(&m->mnt, mnt->mnt_mountpoint);
365 if (child && list_empty(&child->mnt_mounts) &&
366 (ret = do_refcount_check(child, 1)))
367 break;
368 }
369 return ret;
370}
371
372/*
373 * Clear MNT_LOCKED when it can be shown to be safe.
374 *
375 * mount_lock lock must be held for write
376 */
377void propagate_mount_unlock(struct mount *mnt)
378{
379 struct mount *parent = mnt->mnt_parent;
380 struct mount *m, *child;
381
382 BUG_ON(parent == mnt);
383
384 for (m = propagation_next(parent, parent); m;
385 m = propagation_next(m, parent)) {
386 child = __lookup_mnt_last(&m->mnt, mnt->mnt_mountpoint);
387 if (child)
388 child->mnt.mnt_flags &= ~MNT_LOCKED;
389 }
390}
391
392/*
393 * Mark all mounts that the MNT_LOCKED logic will allow to be unmounted.
394 */
395static void mark_umount_candidates(struct mount *mnt)
396{
397 struct mount *parent = mnt->mnt_parent;
398 struct mount *m;
399
400 BUG_ON(parent == mnt);
401
402 for (m = propagation_next(parent, parent); m;
403 m = propagation_next(m, parent)) {
404 struct mount *child = __lookup_mnt_last(&m->mnt,
405 mnt->mnt_mountpoint);
406 if (child && (!IS_MNT_LOCKED(child) || IS_MNT_MARKED(m))) {
407 SET_MNT_MARK(child);
408 }
409 }
410}
411
412/*
413 * NOTE: unmounting 'mnt' naturally propagates to all other mounts its
414 * parent propagates to.
415 */
416static void __propagate_umount(struct mount *mnt)
417{
418 struct mount *parent = mnt->mnt_parent;
419 struct mount *m;
420
421 BUG_ON(parent == mnt);
422
423 for (m = propagation_next(parent, parent); m;
424 m = propagation_next(m, parent)) {
425
426 struct mount *child = __lookup_mnt_last(&m->mnt,
427 mnt->mnt_mountpoint);
428 /*
429 * umount the child only if the child has no children
430 * and the child is marked safe to unmount.
431 */
432 if (!child || !IS_MNT_MARKED(child))
433 continue;
434 CLEAR_MNT_MARK(child);
435 if (list_empty(&child->mnt_mounts)) {
436 list_del_init(&child->mnt_child);
437 child->mnt.mnt_flags |= MNT_UMOUNT;
438 list_move_tail(&child->mnt_list, &mnt->mnt_list);
439 }
440 }
441}
442
443/*
444 * collect all mounts that receive propagation from the mount in @list,
445 * and return these additional mounts in the same list.
446 * @list: the list of mounts to be unmounted.
447 *
448 * vfsmount lock must be held for write
449 */
450int propagate_umount(struct list_head *list)
451{
452 struct mount *mnt;
453
454 list_for_each_entry_reverse(mnt, list, mnt_list)
455 mark_umount_candidates(mnt);
456
457 list_for_each_entry(mnt, list, mnt_list)
458 __propagate_umount(mnt);
459 return 0;
460}
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}