projects/linux·blob v2.6.21 · refs

302 lines · 7.6 KiB

1/*
2 * linux/fs/pnode.c
3 *
4 * (C) Copyright IBM Corporation 2005.
5 * Released under GPL v2.
6 * Author : Ram Pai ([email protected])
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_entry(p->next,
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}