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 "pnode.h"
13
14/* return the next shared peer mount of @p */
15static inline struct vfsmount *next_peer(struct vfsmount *p)
16{
17	return list_entry(p->mnt_share.next, struct vfsmount, mnt_share);
18}
19
20static inline struct vfsmount *first_slave(struct vfsmount *p)
21{
22	return list_entry(p->mnt_slave_list.next, struct vfsmount, mnt_slave);
23}
24
25static inline struct vfsmount *next_slave(struct vfsmount *p)
26{
27	return list_entry(p->mnt_slave.next, struct vfsmount, mnt_slave);
28}
29
30static int do_make_slave(struct vfsmount *mnt)
31{
32	struct vfsmount *peer_mnt = mnt, *master = mnt->mnt_master;
33	struct vfsmount *slave_mnt;
34
35	/*
36	 * slave 'mnt' to a peer mount that has the
37	 * same root dentry. If none is available than
38	 * slave it to anything that is available.
39	 */
40	while ((peer_mnt = next_peer(peer_mnt)) != mnt &&
41	       peer_mnt->mnt_root != mnt->mnt_root) ;
42
43	if (peer_mnt == mnt) {
44		peer_mnt = next_peer(mnt);
45		if (peer_mnt == mnt)
46			peer_mnt = NULL;
47	}
48	list_del_init(&mnt->mnt_share);
49
50	if (peer_mnt)
51		master = peer_mnt;
52
53	if (master) {
54		list_for_each_entry(slave_mnt, &mnt->mnt_slave_list, mnt_slave)
55			slave_mnt->mnt_master = master;
56		list_move(&mnt->mnt_slave, &master->mnt_slave_list);
57		list_splice(&mnt->mnt_slave_list, master->mnt_slave_list.prev);
58		INIT_LIST_HEAD(&mnt->mnt_slave_list);
59	} else {
60		struct list_head *p = &mnt->mnt_slave_list;
61		while (!list_empty(p)) {
62                        slave_mnt = list_first_entry(p,
63					struct vfsmount, mnt_slave);
64			list_del_init(&slave_mnt->mnt_slave);
65			slave_mnt->mnt_master = NULL;
66		}
67	}
68	mnt->mnt_master = master;
69	CLEAR_MNT_SHARED(mnt);
70	INIT_LIST_HEAD(&mnt->mnt_slave_list);
71	return 0;
72}
73
74void change_mnt_propagation(struct vfsmount *mnt, int type)
75{
76	if (type == MS_SHARED) {
77		set_mnt_shared(mnt);
78		return;
79	}
80	do_make_slave(mnt);
81	if (type != MS_SLAVE) {
82		list_del_init(&mnt->mnt_slave);
83		mnt->mnt_master = NULL;
84		if (type == MS_UNBINDABLE)
85			mnt->mnt_flags |= MNT_UNBINDABLE;
86	}
87}
88
89/*
90 * get the next mount in the propagation tree.
91 * @m: the mount seen last
92 * @origin: the original mount from where the tree walk initiated
93 */
94static struct vfsmount *propagation_next(struct vfsmount *m,
95					 struct vfsmount *origin)
96{
97	/* are there any slaves of this mount? */
98	if (!IS_MNT_NEW(m) && !list_empty(&m->mnt_slave_list))
99		return first_slave(m);
100
101	while (1) {
102		struct vfsmount *next;
103		struct vfsmount *master = m->mnt_master;
104
105		if (master == origin->mnt_master) {
106			next = next_peer(m);
107			return ((next == origin) ? NULL : next);
108		} else if (m->mnt_slave.next != &master->mnt_slave_list)
109			return next_slave(m);
110
111		/* back at master */
112		m = master;
113	}
114}
115
116/*
117 * return the source mount to be used for cloning
118 *
119 * @dest 	the current destination mount
120 * @last_dest  	the last seen destination mount
121 * @last_src  	the last seen source mount
122 * @type	return CL_SLAVE if the new mount has to be
123 * 		cloned as a slave.
124 */
125static struct vfsmount *get_source(struct vfsmount *dest,
126					struct vfsmount *last_dest,
127					struct vfsmount *last_src,
128					int *type)
129{
130	struct vfsmount *p_last_src = NULL;
131	struct vfsmount *p_last_dest = NULL;
132	*type = CL_PROPAGATION;
133
134	if (IS_MNT_SHARED(dest))
135		*type |= CL_MAKE_SHARED;
136
137	while (last_dest != dest->mnt_master) {
138		p_last_dest = last_dest;
139		p_last_src = last_src;
140		last_dest = last_dest->mnt_master;
141		last_src = last_src->mnt_master;
142	}
143
144	if (p_last_dest) {
145		do {
146			p_last_dest = next_peer(p_last_dest);
147		} while (IS_MNT_NEW(p_last_dest));
148	}
149
150	if (dest != p_last_dest) {
151		*type |= CL_SLAVE;
152		return last_src;
153	} else
154		return p_last_src;
155}
156
157/*
158 * mount 'source_mnt' under the destination 'dest_mnt' at
159 * dentry 'dest_dentry'. And propagate that mount to
160 * all the peer and slave mounts of 'dest_mnt'.
161 * Link all the new mounts into a propagation tree headed at
162 * source_mnt. Also link all the new mounts using ->mnt_list
163 * headed at source_mnt's ->mnt_list
164 *
165 * @dest_mnt: destination mount.
166 * @dest_dentry: destination dentry.
167 * @source_mnt: source mount.
168 * @tree_list : list of heads of trees to be attached.
169 */
170int propagate_mnt(struct vfsmount *dest_mnt, struct dentry *dest_dentry,
171		    struct vfsmount *source_mnt, struct list_head *tree_list)
172{
173	struct vfsmount *m, *child;
174	int ret = 0;
175	struct vfsmount *prev_dest_mnt = dest_mnt;
176	struct vfsmount *prev_src_mnt  = source_mnt;
177	LIST_HEAD(tmp_list);
178	LIST_HEAD(umount_list);
179
180	for (m = propagation_next(dest_mnt, dest_mnt); m;
181			m = propagation_next(m, dest_mnt)) {
182		int type;
183		struct vfsmount *source;
184
185		if (IS_MNT_NEW(m))
186			continue;
187
188		source =  get_source(m, prev_dest_mnt, prev_src_mnt, &type);
189
190		if (!(child = copy_tree(source, source->mnt_root, type))) {
191			ret = -ENOMEM;
192			list_splice(tree_list, tmp_list.prev);
193			goto out;
194		}
195
196		if (is_subdir(dest_dentry, m->mnt_root)) {
197			mnt_set_mountpoint(m, dest_dentry, child);
198			list_add_tail(&child->mnt_hash, tree_list);
199		} else {
200			/*
201			 * This can happen if the parent mount was bind mounted
202			 * on some subdirectory of a shared/slave mount.
203			 */
204			list_add_tail(&child->mnt_hash, &tmp_list);
205		}
206		prev_dest_mnt = m;
207		prev_src_mnt  = child;
208	}
209out:
210	spin_lock(&vfsmount_lock);
211	while (!list_empty(&tmp_list)) {
212		child = list_entry(tmp_list.next, struct vfsmount, mnt_hash);
213		list_del_init(&child->mnt_hash);
214		umount_tree(child, 0, &umount_list);
215	}
216	spin_unlock(&vfsmount_lock);
217	release_mounts(&umount_list);
218	return ret;
219}
220
221/*
222 * return true if the refcount is greater than count
223 */
224static inline int do_refcount_check(struct vfsmount *mnt, int count)
225{
226	int mycount = atomic_read(&mnt->mnt_count);
227	return (mycount > count);
228}
229
230/*
231 * check if the mount 'mnt' can be unmounted successfully.
232 * @mnt: the mount to be checked for unmount
233 * NOTE: unmounting 'mnt' would naturally propagate to all
234 * other mounts its parent propagates to.
235 * Check if any of these mounts that **do not have submounts**
236 * have more references than 'refcnt'. If so return busy.
237 */
238int propagate_mount_busy(struct vfsmount *mnt, int refcnt)
239{
240	struct vfsmount *m, *child;
241	struct vfsmount *parent = mnt->mnt_parent;
242	int ret = 0;
243
244	if (mnt == parent)
245		return do_refcount_check(mnt, refcnt);
246
247	/*
248	 * quickly check if the current mount can be unmounted.
249	 * If not, we don't have to go checking for all other
250	 * mounts
251	 */
252	if (!list_empty(&mnt->mnt_mounts) || do_refcount_check(mnt, refcnt))
253		return 1;
254
255	for (m = propagation_next(parent, parent); m;
256	     		m = propagation_next(m, parent)) {
257		child = __lookup_mnt(m, mnt->mnt_mountpoint, 0);
258		if (child && list_empty(&child->mnt_mounts) &&
259		    (ret = do_refcount_check(child, 1)))
260			break;
261	}
262	return ret;
263}
264
265/*
266 * NOTE: unmounting 'mnt' naturally propagates to all other mounts its
267 * parent propagates to.
268 */
269static void __propagate_umount(struct vfsmount *mnt)
270{
271	struct vfsmount *parent = mnt->mnt_parent;
272	struct vfsmount *m;
273
274	BUG_ON(parent == mnt);
275
276	for (m = propagation_next(parent, parent); m;
277			m = propagation_next(m, parent)) {
278
279		struct vfsmount *child = __lookup_mnt(m,
280					mnt->mnt_mountpoint, 0);
281		/*
282		 * umount the child only if the child has no
283		 * other children
284		 */
285		if (child && list_empty(&child->mnt_mounts))
286			list_move_tail(&child->mnt_hash, &mnt->mnt_hash);
287	}
288}
289
290/*
291 * collect all mounts that receive propagation from the mount in @list,
292 * and return these additional mounts in the same list.
293 * @list: the list of mounts to be unmounted.
294 */
295int propagate_umount(struct list_head *list)
296{
297	struct vfsmount *mnt;
298
299	list_for_each_entry(mnt, list, mnt_hash)
300		__propagate_umount(mnt);
301	return 0;
302}
303