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Linux/fs/pnode.c

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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 */
 17 static inline struct mount *next_peer(struct mount *p)
 18 {
 19         return list_entry(p->mnt_share.next, struct mount, mnt_share);
 20 }
 21 
 22 static inline struct mount *first_slave(struct mount *p)
 23 {
 24         return list_entry(p->mnt_slave_list.next, struct mount, mnt_slave);
 25 }
 26 
 27 static inline struct mount *next_slave(struct mount *p)
 28 {
 29         return list_entry(p->mnt_slave.next, struct mount, mnt_slave);
 30 }
 31 
 32 static 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  */
 55 int 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 
 68 static 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  */
119 void 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  */
146 static 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 
167 static 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 */
200 static struct user_namespace *user_ns;
201 static struct mount *last_dest, *last_source, *dest_master;
202 static struct mountpoint *mp;
203 static struct hlist_head *list;
204 
205 static int propagate_one(struct mount *m)
206 {
207         struct mount *child;
208         int type;
209         /* skip ones added by this propagate_mnt() */
210         if (IS_MNT_NEW(m))
211                 return 0;
212         /* skip if mountpoint isn't covered by it */
213         if (!is_subdir(mp->m_dentry, m->mnt.mnt_root))
214                 return 0;
215         if (m->mnt_group_id == last_dest->mnt_group_id) {
216                 type = CL_MAKE_SHARED;
217         } else {
218                 struct mount *n, *p;
219                 for (n = m; ; n = p) {
220                         p = n->mnt_master;
221                         if (p == dest_master || IS_MNT_MARKED(p)) {
222                                 while (last_dest->mnt_master != p) {
223                                         last_source = last_source->mnt_master;
224                                         last_dest = last_source->mnt_parent;
225                                 }
226                                 if (n->mnt_group_id != last_dest->mnt_group_id) {
227                                         last_source = last_source->mnt_master;
228                                         last_dest = last_source->mnt_parent;
229                                 }
230                                 break;
231                         }
232                 }
233                 type = CL_SLAVE;
234                 /* beginning of peer group among the slaves? */
235                 if (IS_MNT_SHARED(m))
236                         type |= CL_MAKE_SHARED;
237         }
238                 
239         /* Notice when we are propagating across user namespaces */
240         if (m->mnt_ns->user_ns != user_ns)
241                 type |= CL_UNPRIVILEGED;
242         child = copy_tree(last_source, last_source->mnt.mnt_root, type);
243         if (IS_ERR(child))
244                 return PTR_ERR(child);
245         mnt_set_mountpoint(m, mp, child);
246         last_dest = m;
247         last_source = child;
248         if (m->mnt_master != dest_master) {
249                 read_seqlock_excl(&mount_lock);
250                 SET_MNT_MARK(m->mnt_master);
251                 read_sequnlock_excl(&mount_lock);
252         }
253         hlist_add_head(&child->mnt_hash, list);
254         return 0;
255 }
256 
257 /*
258  * mount 'source_mnt' under the destination 'dest_mnt' at
259  * dentry 'dest_dentry'. And propagate that mount to
260  * all the peer and slave mounts of 'dest_mnt'.
261  * Link all the new mounts into a propagation tree headed at
262  * source_mnt. Also link all the new mounts using ->mnt_list
263  * headed at source_mnt's ->mnt_list
264  *
265  * @dest_mnt: destination mount.
266  * @dest_dentry: destination dentry.
267  * @source_mnt: source mount.
268  * @tree_list : list of heads of trees to be attached.
269  */
270 int propagate_mnt(struct mount *dest_mnt, struct mountpoint *dest_mp,
271                     struct mount *source_mnt, struct hlist_head *tree_list)
272 {
273         struct mount *m, *n;
274         int ret = 0;
275 
276         /*
277          * we don't want to bother passing tons of arguments to
278          * propagate_one(); everything is serialized by namespace_sem,
279          * so globals will do just fine.
280          */
281         user_ns = current->nsproxy->mnt_ns->user_ns;
282         last_dest = dest_mnt;
283         last_source = source_mnt;
284         mp = dest_mp;
285         list = tree_list;
286         dest_master = dest_mnt->mnt_master;
287 
288         /* all peers of dest_mnt, except dest_mnt itself */
289         for (n = next_peer(dest_mnt); n != dest_mnt; n = next_peer(n)) {
290                 ret = propagate_one(n);
291                 if (ret)
292                         goto out;
293         }
294 
295         /* all slave groups */
296         for (m = next_group(dest_mnt, dest_mnt); m;
297                         m = next_group(m, dest_mnt)) {
298                 /* everything in that slave group */
299                 n = m;
300                 do {
301                         ret = propagate_one(n);
302                         if (ret)
303                                 goto out;
304                         n = next_peer(n);
305                 } while (n != m);
306         }
307 out:
308         read_seqlock_excl(&mount_lock);
309         hlist_for_each_entry(n, tree_list, mnt_hash) {
310                 m = n->mnt_parent;
311                 if (m->mnt_master != dest_mnt->mnt_master)
312                         CLEAR_MNT_MARK(m->mnt_master);
313         }
314         read_sequnlock_excl(&mount_lock);
315         return ret;
316 }
317 
318 /*
319  * return true if the refcount is greater than count
320  */
321 static inline int do_refcount_check(struct mount *mnt, int count)
322 {
323         return mnt_get_count(mnt) > count;
324 }
325 
326 /*
327  * check if the mount 'mnt' can be unmounted successfully.
328  * @mnt: the mount to be checked for unmount
329  * NOTE: unmounting 'mnt' would naturally propagate to all
330  * other mounts its parent propagates to.
331  * Check if any of these mounts that **do not have submounts**
332  * have more references than 'refcnt'. If so return busy.
333  *
334  * vfsmount lock must be held for write
335  */
336 int propagate_mount_busy(struct mount *mnt, int refcnt)
337 {
338         struct mount *m, *child;
339         struct mount *parent = mnt->mnt_parent;
340         int ret = 0;
341 
342         if (mnt == parent)
343                 return do_refcount_check(mnt, refcnt);
344 
345         /*
346          * quickly check if the current mount can be unmounted.
347          * If not, we don't have to go checking for all other
348          * mounts
349          */
350         if (!list_empty(&mnt->mnt_mounts) || do_refcount_check(mnt, refcnt))
351                 return 1;
352 
353         for (m = propagation_next(parent, parent); m;
354                         m = propagation_next(m, parent)) {
355                 child = __lookup_mnt_last(&m->mnt, mnt->mnt_mountpoint);
356                 if (child && list_empty(&child->mnt_mounts) &&
357                     (ret = do_refcount_check(child, 1)))
358                         break;
359         }
360         return ret;
361 }
362 
363 /*
364  * NOTE: unmounting 'mnt' naturally propagates to all other mounts its
365  * parent propagates to.
366  */
367 static void __propagate_umount(struct mount *mnt)
368 {
369         struct mount *parent = mnt->mnt_parent;
370         struct mount *m;
371 
372         BUG_ON(parent == mnt);
373 
374         for (m = propagation_next(parent, parent); m;
375                         m = propagation_next(m, parent)) {
376 
377                 struct mount *child = __lookup_mnt_last(&m->mnt,
378                                                 mnt->mnt_mountpoint);
379                 /*
380                  * umount the child only if the child has no
381                  * other children
382                  */
383                 if (child && list_empty(&child->mnt_mounts)) {
384                         hlist_del_init_rcu(&child->mnt_hash);
385                         hlist_add_before_rcu(&child->mnt_hash, &mnt->mnt_hash);
386                 }
387         }
388 }
389 
390 /*
391  * collect all mounts that receive propagation from the mount in @list,
392  * and return these additional mounts in the same list.
393  * @list: the list of mounts to be unmounted.
394  *
395  * vfsmount lock must be held for write
396  */
397 int propagate_umount(struct hlist_head *list)
398 {
399         struct mount *mnt;
400 
401         hlist_for_each_entry(mnt, list, mnt_hash)
402                 __propagate_umount(mnt);
403         return 0;
404 }
405 

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