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 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
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 *
151 * Note that peer groups form contiguous segments of slave lists.
152 * We rely on that in get_source() to be able to find out if
153 * vfsmount found while iterating with propagation_next() is
154 * a peer of one we'd found earlier.
155 */
156static struct vfsmount *propagation_next(struct vfsmount *m,
157                     struct vfsmount *origin)
158{
159    /* are there any slaves of this mount? */
160    if (!IS_MNT_NEW(m) && !list_empty(&m->mnt_slave_list))
161        return first_slave(m);
162
163    while (1) {
164        struct vfsmount *next;
165        struct vfsmount *master = m->mnt_master;
166
167        if (master == origin->mnt_master) {
168            next = next_peer(m);
169            return ((next == origin) ? NULL : next);
170        } else if (m->mnt_slave.next != &master->mnt_slave_list)
171            return next_slave(m);
172
173        /* back at master */
174        m = master;
175    }
176}
177
178/*
179 * return the source mount to be used for cloning
180 *
181 * @dest the current destination mount
182 * @last_dest the last seen destination mount
183 * @last_src the last seen source mount
184 * @type return CL_SLAVE if the new mount has to be
185 * cloned as a slave.
186 */
187static struct vfsmount *get_source(struct vfsmount *dest,
188                    struct vfsmount *last_dest,
189                    struct vfsmount *last_src,
190                    int *type)
191{
192    struct vfsmount *p_last_src = NULL;
193    struct vfsmount *p_last_dest = NULL;
194
195    while (last_dest != dest->mnt_master) {
196        p_last_dest = last_dest;
197        p_last_src = last_src;
198        last_dest = last_dest->mnt_master;
199        last_src = last_src->mnt_master;
200    }
201
202    if (p_last_dest) {
203        do {
204            p_last_dest = next_peer(p_last_dest);
205        } while (IS_MNT_NEW(p_last_dest));
206        /* is that a peer of the earlier? */
207        if (dest == p_last_dest) {
208            *type = CL_MAKE_SHARED;
209            return p_last_src;
210        }
211    }
212    /* slave of the earlier, then */
213    *type = CL_SLAVE;
214    /* beginning of peer group among the slaves? */
215    if (IS_MNT_SHARED(dest))
216        *type |= CL_MAKE_SHARED;
217    return last_src;
218}
219
220/*
221 * mount 'source_mnt' under the destination 'dest_mnt' at
222 * dentry 'dest_dentry'. And propagate that mount to
223 * all the peer and slave mounts of 'dest_mnt'.
224 * Link all the new mounts into a propagation tree headed at
225 * source_mnt. Also link all the new mounts using ->mnt_list
226 * headed at source_mnt's ->mnt_list
227 *
228 * @dest_mnt: destination mount.
229 * @dest_dentry: destination dentry.
230 * @source_mnt: source mount.
231 * @tree_list : list of heads of trees to be attached.
232 */
233int propagate_mnt(struct vfsmount *dest_mnt, struct dentry *dest_dentry,
234            struct vfsmount *source_mnt, struct list_head *tree_list)
235{
236    struct vfsmount *m, *child;
237    int ret = 0;
238    struct vfsmount *prev_dest_mnt = dest_mnt;
239    struct vfsmount *prev_src_mnt = source_mnt;
240    LIST_HEAD(tmp_list);
241    LIST_HEAD(umount_list);
242
243    for (m = propagation_next(dest_mnt, dest_mnt); m;
244            m = propagation_next(m, dest_mnt)) {
245        int type;
246        struct vfsmount *source;
247
248        if (IS_MNT_NEW(m))
249            continue;
250
251        source = get_source(m, prev_dest_mnt, prev_src_mnt, &type);
252
253        if (!(child = copy_tree(source, source->mnt_root, type))) {
254            ret = -ENOMEM;
255            list_splice(tree_list, tmp_list.prev);
256            goto out;
257        }
258
259        if (is_subdir(dest_dentry, m->mnt_root)) {
260            mnt_set_mountpoint(m, dest_dentry, child);
261            list_add_tail(&child->mnt_hash, tree_list);
262        } else {
263            /*
264             * This can happen if the parent mount was bind mounted
265             * on some subdirectory of a shared/slave mount.
266             */
267            list_add_tail(&child->mnt_hash, &tmp_list);
268        }
269        prev_dest_mnt = m;
270        prev_src_mnt = child;
271    }
272out:
273    spin_lock(&vfsmount_lock);
274    while (!list_empty(&tmp_list)) {
275        child = list_first_entry(&tmp_list, struct vfsmount, mnt_hash);
276        umount_tree(child, 0, &umount_list);
277    }
278    spin_unlock(&vfsmount_lock);
279    release_mounts(&umount_list);
280    return ret;
281}
282
283/*
284 * return true if the refcount is greater than count
285 */
286static inline int do_refcount_check(struct vfsmount *mnt, int count)
287{
288    int mycount = atomic_read(&mnt->mnt_count) - mnt->mnt_ghosts;
289    return (mycount > count);
290}
291
292/*
293 * check if the mount 'mnt' can be unmounted successfully.
294 * @mnt: the mount to be checked for unmount
295 * NOTE: unmounting 'mnt' would naturally propagate to all
296 * other mounts its parent propagates to.
297 * Check if any of these mounts that **do not have submounts**
298 * have more references than 'refcnt'. If so return busy.
299 */
300int propagate_mount_busy(struct vfsmount *mnt, int refcnt)
301{
302    struct vfsmount *m, *child;
303    struct vfsmount *parent = mnt->mnt_parent;
304    int ret = 0;
305
306    if (mnt == parent)
307        return do_refcount_check(mnt, refcnt);
308
309    /*
310     * quickly check if the current mount can be unmounted.
311     * If not, we don't have to go checking for all other
312     * mounts
313     */
314    if (!list_empty(&mnt->mnt_mounts) || do_refcount_check(mnt, refcnt))
315        return 1;
316
317    for (m = propagation_next(parent, parent); m;
318                 m = propagation_next(m, parent)) {
319        child = __lookup_mnt(m, mnt->mnt_mountpoint, 0);
320        if (child && list_empty(&child->mnt_mounts) &&
321            (ret = do_refcount_check(child, 1)))
322            break;
323    }
324    return ret;
325}
326
327/*
328 * NOTE: unmounting 'mnt' naturally propagates to all other mounts its
329 * parent propagates to.
330 */
331static void __propagate_umount(struct vfsmount *mnt)
332{
333    struct vfsmount *parent = mnt->mnt_parent;
334    struct vfsmount *m;
335
336    BUG_ON(parent == mnt);
337
338    for (m = propagation_next(parent, parent); m;
339            m = propagation_next(m, parent)) {
340
341        struct vfsmount *child = __lookup_mnt(m,
342                    mnt->mnt_mountpoint, 0);
343        /*
344         * umount the child only if the child has no
345         * other children
346         */
347        if (child && list_empty(&child->mnt_mounts))
348            list_move_tail(&child->mnt_hash, &mnt->mnt_hash);
349    }
350}
351
352/*
353 * collect all mounts that receive propagation from the mount in @list,
354 * and return these additional mounts in the same list.
355 * @list: the list of mounts to be unmounted.
356 */
357int propagate_umount(struct list_head *list)
358{
359    struct vfsmount *mnt;
360
361    list_for_each_entry(mnt, list, mnt_hash)
362        __propagate_umount(mnt);
363    return 0;
364}
365

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