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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 "internal.h"
 13 #include "pnode.h"
 14 
 15 /* return the next shared peer mount of @p */
 16 static inline struct vfsmount *next_peer(struct vfsmount *p)
 17 {
 18         return list_entry(p->mnt_share.next, struct vfsmount, mnt_share);
 19 }
 20 
 21 static inline struct vfsmount *first_slave(struct vfsmount *p)
 22 {
 23         return list_entry(p->mnt_slave_list.next, struct vfsmount, mnt_slave);
 24 }
 25 
 26 static 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  */
 36 static 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 
 46 static 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  */
 69 int 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 
 82 static 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  */
132 void 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  */
159 static 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  */
190 static 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  */
236 int 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         }
275 out:
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  */
289 static 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  */
305 int 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  */
336 static 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  */
364 int 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 }
372 

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