Root/fs/pnode.c

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 */
16static inline struct vfsmount *next_peer(struct vfsmount *p)
17{
18    return list_entry(p->mnt_share.next, struct vfsmount, mnt_share);
19}
20
21static inline struct vfsmount *first_slave(struct vfsmount *p)
22{
23    return list_entry(p->mnt_slave_list.next, struct vfsmount, mnt_slave);
24}
25
26static 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 */
36static 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
46static 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 */
69int 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
82static 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 than
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
129void change_mnt_propagation(struct vfsmount *mnt, int type)
130{
131    if (type == MS_SHARED) {
132        set_mnt_shared(mnt);
133        return;
134    }
135    do_make_slave(mnt);
136    if (type != MS_SLAVE) {
137        list_del_init(&mnt->mnt_slave);
138        mnt->mnt_master = NULL;
139        if (type == MS_UNBINDABLE)
140            mnt->mnt_flags |= MNT_UNBINDABLE;
141        else
142            mnt->mnt_flags &= ~MNT_UNBINDABLE;
143    }
144}
145
146/*
147 * get the next mount in the propagation tree.
148 * @m: the mount seen last
149 * @origin: the original mount from where the tree walk initiated
150 */
151static struct vfsmount *propagation_next(struct vfsmount *m,
152                     struct vfsmount *origin)
153{
154    /* are there any slaves of this mount? */
155    if (!IS_MNT_NEW(m) && !list_empty(&m->mnt_slave_list))
156        return first_slave(m);
157
158    while (1) {
159        struct vfsmount *next;
160        struct vfsmount *master = m->mnt_master;
161
162        if (master == origin->mnt_master) {
163            next = next_peer(m);
164            return ((next == origin) ? NULL : next);
165        } else if (m->mnt_slave.next != &master->mnt_slave_list)
166            return next_slave(m);
167
168        /* back at master */
169        m = master;
170    }
171}
172
173/*
174 * return the source mount to be used for cloning
175 *
176 * @dest the current destination mount
177 * @last_dest the last seen destination mount
178 * @last_src the last seen source mount
179 * @type return CL_SLAVE if the new mount has to be
180 * cloned as a slave.
181 */
182static struct vfsmount *get_source(struct vfsmount *dest,
183                    struct vfsmount *last_dest,
184                    struct vfsmount *last_src,
185                    int *type)
186{
187    struct vfsmount *p_last_src = NULL;
188    struct vfsmount *p_last_dest = NULL;
189    *type = CL_PROPAGATION;
190
191    if (IS_MNT_SHARED(dest))
192        *type |= CL_MAKE_SHARED;
193
194    while (last_dest != dest->mnt_master) {
195        p_last_dest = last_dest;
196        p_last_src = last_src;
197        last_dest = last_dest->mnt_master;
198        last_src = last_src->mnt_master;
199    }
200
201    if (p_last_dest) {
202        do {
203            p_last_dest = next_peer(p_last_dest);
204        } while (IS_MNT_NEW(p_last_dest));
205    }
206
207    if (dest != p_last_dest) {
208        *type |= CL_SLAVE;
209        return last_src;
210    } else
211        return p_last_src;
212}
213
214/*
215 * mount 'source_mnt' under the destination 'dest_mnt' at
216 * dentry 'dest_dentry'. And propagate that mount to
217 * all the peer and slave mounts of 'dest_mnt'.
218 * Link all the new mounts into a propagation tree headed at
219 * source_mnt. Also link all the new mounts using ->mnt_list
220 * headed at source_mnt's ->mnt_list
221 *
222 * @dest_mnt: destination mount.
223 * @dest_dentry: destination dentry.
224 * @source_mnt: source mount.
225 * @tree_list : list of heads of trees to be attached.
226 */
227int propagate_mnt(struct vfsmount *dest_mnt, struct dentry *dest_dentry,
228            struct vfsmount *source_mnt, struct list_head *tree_list)
229{
230    struct vfsmount *m, *child;
231    int ret = 0;
232    struct vfsmount *prev_dest_mnt = dest_mnt;
233    struct vfsmount *prev_src_mnt = source_mnt;
234    LIST_HEAD(tmp_list);
235    LIST_HEAD(umount_list);
236
237    for (m = propagation_next(dest_mnt, dest_mnt); m;
238            m = propagation_next(m, dest_mnt)) {
239        int type;
240        struct vfsmount *source;
241
242        if (IS_MNT_NEW(m))
243            continue;
244
245        source = get_source(m, prev_dest_mnt, prev_src_mnt, &type);
246
247        if (!(child = copy_tree(source, source->mnt_root, type))) {
248            ret = -ENOMEM;
249            list_splice(tree_list, tmp_list.prev);
250            goto out;
251        }
252
253        if (is_subdir(dest_dentry, m->mnt_root)) {
254            mnt_set_mountpoint(m, dest_dentry, child);
255            list_add_tail(&child->mnt_hash, tree_list);
256        } else {
257            /*
258             * This can happen if the parent mount was bind mounted
259             * on some subdirectory of a shared/slave mount.
260             */
261            list_add_tail(&child->mnt_hash, &tmp_list);
262        }
263        prev_dest_mnt = m;
264        prev_src_mnt = child;
265    }
266out:
267    spin_lock(&vfsmount_lock);
268    while (!list_empty(&tmp_list)) {
269        child = list_first_entry(&tmp_list, struct vfsmount, mnt_hash);
270        umount_tree(child, 0, &umount_list);
271    }
272    spin_unlock(&vfsmount_lock);
273    release_mounts(&umount_list);
274    return ret;
275}
276
277/*
278 * return true if the refcount is greater than count
279 */
280static inline int do_refcount_check(struct vfsmount *mnt, int count)
281{
282    int mycount = atomic_read(&mnt->mnt_count) - mnt->mnt_ghosts;
283    return (mycount > count);
284}
285
286/*
287 * check if the mount 'mnt' can be unmounted successfully.
288 * @mnt: the mount to be checked for unmount
289 * NOTE: unmounting 'mnt' would naturally propagate to all
290 * other mounts its parent propagates to.
291 * Check if any of these mounts that **do not have submounts**
292 * have more references than 'refcnt'. If so return busy.
293 */
294int propagate_mount_busy(struct vfsmount *mnt, int refcnt)
295{
296    struct vfsmount *m, *child;
297    struct vfsmount *parent = mnt->mnt_parent;
298    int ret = 0;
299
300    if (mnt == parent)
301        return do_refcount_check(mnt, refcnt);
302
303    /*
304     * quickly check if the current mount can be unmounted.
305     * If not, we don't have to go checking for all other
306     * mounts
307     */
308    if (!list_empty(&mnt->mnt_mounts) || do_refcount_check(mnt, refcnt))
309        return 1;
310
311    for (m = propagation_next(parent, parent); m;
312                 m = propagation_next(m, parent)) {
313        child = __lookup_mnt(m, mnt->mnt_mountpoint, 0);
314        if (child && list_empty(&child->mnt_mounts) &&
315            (ret = do_refcount_check(child, 1)))
316            break;
317    }
318    return ret;
319}
320
321/*
322 * NOTE: unmounting 'mnt' naturally propagates to all other mounts its
323 * parent propagates to.
324 */
325static void __propagate_umount(struct vfsmount *mnt)
326{
327    struct vfsmount *parent = mnt->mnt_parent;
328    struct vfsmount *m;
329
330    BUG_ON(parent == mnt);
331
332    for (m = propagation_next(parent, parent); m;
333            m = propagation_next(m, parent)) {
334
335        struct vfsmount *child = __lookup_mnt(m,
336                    mnt->mnt_mountpoint, 0);
337        /*
338         * umount the child only if the child has no
339         * other children
340         */
341        if (child && list_empty(&child->mnt_mounts))
342            list_move_tail(&child->mnt_hash, &mnt->mnt_hash);
343    }
344}
345
346/*
347 * collect all mounts that receive propagation from the mount in @list,
348 * and return these additional mounts in the same list.
349 * @list: the list of mounts to be unmounted.
350 */
351int propagate_umount(struct list_head *list)
352{
353    struct vfsmount *mnt;
354
355    list_for_each_entry(mnt, list, mnt_hash)
356        __propagate_umount(mnt);
357    return 0;
358}
359

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