xref: /openbmc/linux/fs/pnode.c (revision e868d61272caa648214046a096e5a6bfc068dc8c)
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 */
15 static inline struct vfsmount *next_peer(struct vfsmount *p)
16 {
17 	return list_entry(p->mnt_share.next, struct vfsmount, mnt_share);
18 }
19 
20 static inline struct vfsmount *first_slave(struct vfsmount *p)
21 {
22 	return list_entry(p->mnt_slave_list.next, struct vfsmount, mnt_slave);
23 }
24 
25 static inline struct vfsmount *next_slave(struct vfsmount *p)
26 {
27 	return list_entry(p->mnt_slave.next, struct vfsmount, mnt_slave);
28 }
29 
30 static 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 
74 void 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  */
94 static 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  */
125 static 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  */
170 int 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 	}
209 out:
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  */
224 static 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  */
238 int 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  */
269 static 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  */
295 int 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