4 * (C) Copyright IBM Corporation 2005.
5 * Released under GPL v2.
6 * Author : Ram Pai (linuxram@us.ibm.com)
9 #include <linux/mnt_namespace.h>
10 #include <linux/mount.h>
15 /* return the next shared peer mount of @p */
16 static inline struct vfsmount
*next_peer(struct vfsmount
*p
)
18 return list_entry(p
->mnt_share
.next
, struct vfsmount
, mnt_share
);
21 static inline struct vfsmount
*first_slave(struct vfsmount
*p
)
23 return list_entry(p
->mnt_slave_list
.next
, struct vfsmount
, mnt_slave
);
26 static inline struct vfsmount
*next_slave(struct vfsmount
*p
)
28 return list_entry(p
->mnt_slave
.next
, struct vfsmount
, mnt_slave
);
32 * Return true if path is reachable from root
34 * namespace_sem is held, and mnt is attached
36 static bool is_path_reachable(struct vfsmount
*mnt
, struct dentry
*dentry
,
37 const struct path
*root
)
39 while (mnt
!= root
->mnt
&& mnt
->mnt_parent
!= mnt
) {
40 dentry
= mnt
->mnt_mountpoint
;
41 mnt
= mnt
->mnt_parent
;
43 return mnt
== root
->mnt
&& is_subdir(dentry
, root
->dentry
);
46 static struct vfsmount
*get_peer_under_root(struct vfsmount
*mnt
,
47 struct mnt_namespace
*ns
,
48 const struct path
*root
)
50 struct vfsmount
*m
= mnt
;
53 /* Check the namespace first for optimization */
54 if (m
->mnt_ns
== ns
&& is_path_reachable(m
, m
->mnt_root
, root
))
64 * Get ID of closest dominating peer group having a representative
65 * under the given root.
67 * Caller must hold namespace_sem
69 int get_dominating_id(struct vfsmount
*mnt
, const struct path
*root
)
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
);
76 return d
->mnt_group_id
;
82 static int do_make_slave(struct vfsmount
*mnt
)
84 struct vfsmount
*peer_mnt
= mnt
, *master
= mnt
->mnt_master
;
85 struct vfsmount
*slave_mnt
;
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.
92 while ((peer_mnt
= next_peer(peer_mnt
)) != mnt
&&
93 peer_mnt
->mnt_root
!= mnt
->mnt_root
) ;
95 if (peer_mnt
== mnt
) {
96 peer_mnt
= next_peer(mnt
);
100 if (IS_MNT_SHARED(mnt
) && list_empty(&mnt
->mnt_share
))
101 mnt_release_group_id(mnt
);
103 list_del_init(&mnt
->mnt_share
);
104 mnt
->mnt_group_id
= 0;
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
);
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
;
124 mnt
->mnt_master
= master
;
125 CLEAR_MNT_SHARED(mnt
);
129 void change_mnt_propagation(struct vfsmount
*mnt
, int type
)
131 if (type
== MS_SHARED
) {
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
;
142 mnt
->mnt_flags
&= ~MNT_UNBINDABLE
;
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
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.
156 static struct vfsmount
*propagation_next(struct vfsmount
*m
,
157 struct vfsmount
*origin
)
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
);
164 struct vfsmount
*next
;
165 struct vfsmount
*master
= m
->mnt_master
;
167 if (master
== origin
->mnt_master
) {
169 return ((next
== origin
) ? NULL
: next
);
170 } else if (m
->mnt_slave
.next
!= &master
->mnt_slave_list
)
171 return next_slave(m
);
179 * return the source mount to be used for cloning
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
187 static struct vfsmount
*get_source(struct vfsmount
*dest
,
188 struct vfsmount
*last_dest
,
189 struct vfsmount
*last_src
,
192 struct vfsmount
*p_last_src
= NULL
;
193 struct vfsmount
*p_last_dest
= NULL
;
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
;
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
;
212 /* slave of the earlier, then */
214 /* beginning of peer group among the slaves? */
215 if (IS_MNT_SHARED(dest
))
216 *type
|= CL_MAKE_SHARED
;
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
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.
233 int propagate_mnt(struct vfsmount
*dest_mnt
, struct dentry
*dest_dentry
,
234 struct vfsmount
*source_mnt
, struct list_head
*tree_list
)
236 struct vfsmount
*m
, *child
;
238 struct vfsmount
*prev_dest_mnt
= dest_mnt
;
239 struct vfsmount
*prev_src_mnt
= source_mnt
;
241 LIST_HEAD(umount_list
);
243 for (m
= propagation_next(dest_mnt
, dest_mnt
); m
;
244 m
= propagation_next(m
, dest_mnt
)) {
246 struct vfsmount
*source
;
251 source
= get_source(m
, prev_dest_mnt
, prev_src_mnt
, &type
);
253 if (!(child
= copy_tree(source
, source
->mnt_root
, type
))) {
255 list_splice(tree_list
, tmp_list
.prev
);
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
);
264 * This can happen if the parent mount was bind mounted
265 * on some subdirectory of a shared/slave mount.
267 list_add_tail(&child
->mnt_hash
, &tmp_list
);
270 prev_src_mnt
= child
;
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
);
278 spin_unlock(&vfsmount_lock
);
279 release_mounts(&umount_list
);
284 * return true if the refcount is greater than count
286 static inline int do_refcount_check(struct vfsmount
*mnt
, int count
)
288 int mycount
= atomic_read(&mnt
->mnt_count
) - mnt
->mnt_ghosts
;
289 return (mycount
> count
);
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.
300 int propagate_mount_busy(struct vfsmount
*mnt
, int refcnt
)
302 struct vfsmount
*m
, *child
;
303 struct vfsmount
*parent
= mnt
->mnt_parent
;
307 return do_refcount_check(mnt
, refcnt
);
310 * quickly check if the current mount can be unmounted.
311 * If not, we don't have to go checking for all other
314 if (!list_empty(&mnt
->mnt_mounts
) || do_refcount_check(mnt
, refcnt
))
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)))
328 * NOTE: unmounting 'mnt' naturally propagates to all other mounts its
329 * parent propagates to.
331 static void __propagate_umount(struct vfsmount
*mnt
)
333 struct vfsmount
*parent
= mnt
->mnt_parent
;
336 BUG_ON(parent
== mnt
);
338 for (m
= propagation_next(parent
, parent
); m
;
339 m
= propagation_next(m
, parent
)) {
341 struct vfsmount
*child
= __lookup_mnt(m
,
342 mnt
->mnt_mountpoint
, 0);
344 * umount the child only if the child has no
347 if (child
&& list_empty(&child
->mnt_mounts
))
348 list_move_tail(&child
->mnt_hash
, &mnt
->mnt_hash
);
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.
357 int propagate_umount(struct list_head
*list
)
359 struct vfsmount
*mnt
;
361 list_for_each_entry(mnt
, list
, mnt_hash
)
362 __propagate_umount(mnt
);
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