nfsd: nfsd should drop CAP_MKNOD for non-root
[linux-2.6/linux-acpi-2.6/ibm-acpi-2.6.git] / fs / pnode.c
blob8d5f392ec3d39fa12a025ec3a6045b7ef8f790a4
1 /*
2 * linux/fs/pnode.c
4 * (C) Copyright IBM Corporation 2005.
5 * Released under GPL v2.
6 * Author : Ram Pai (linuxram@us.ibm.com)
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"
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;
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;
57 m = next_peer(m);
58 } while (m != mnt);
60 return NULL;
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)
71 struct vfsmount *m;
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;
79 return 0;
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 than
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);
97 if (peer_mnt == mnt)
98 peer_mnt = NULL;
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;
106 if (peer_mnt)
107 master = peer_mnt;
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;
124 mnt->mnt_master = master;
125 CLEAR_MNT_SHARED(mnt);
126 return 0;
129 void change_mnt_propagation(struct vfsmount *mnt, int type)
131 if (type == MS_SHARED) {
132 set_mnt_shared(mnt);
133 return;
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;
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 static struct vfsmount *propagation_next(struct vfsmount *m,
152 struct vfsmount *origin)
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);
158 while (1) {
159 struct vfsmount *next;
160 struct vfsmount *master = m->mnt_master;
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);
168 /* back at master */
169 m = master;
174 * return the source mount to be used for cloning
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.
182 static struct vfsmount *get_source(struct vfsmount *dest,
183 struct vfsmount *last_dest,
184 struct vfsmount *last_src,
185 int *type)
187 struct vfsmount *p_last_src = NULL;
188 struct vfsmount *p_last_dest = NULL;
189 *type = CL_PROPAGATION;
191 if (IS_MNT_SHARED(dest))
192 *type |= CL_MAKE_SHARED;
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;
201 if (p_last_dest) {
202 do {
203 p_last_dest = next_peer(p_last_dest);
204 } while (IS_MNT_NEW(p_last_dest));
207 if (dest != p_last_dest) {
208 *type |= CL_SLAVE;
209 return last_src;
210 } else
211 return p_last_src;
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
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.
227 int propagate_mnt(struct vfsmount *dest_mnt, struct dentry *dest_dentry,
228 struct vfsmount *source_mnt, struct list_head *tree_list)
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);
237 for (m = propagation_next(dest_mnt, dest_mnt); m;
238 m = propagation_next(m, dest_mnt)) {
239 int type;
240 struct vfsmount *source;
242 if (IS_MNT_NEW(m))
243 continue;
245 source = get_source(m, prev_dest_mnt, prev_src_mnt, &type);
247 if (!(child = copy_tree(source, source->mnt_root, type))) {
248 ret = -ENOMEM;
249 list_splice(tree_list, tmp_list.prev);
250 goto out;
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 {
258 * This can happen if the parent mount was bind mounted
259 * on some subdirectory of a shared/slave mount.
261 list_add_tail(&child->mnt_hash, &tmp_list);
263 prev_dest_mnt = m;
264 prev_src_mnt = child;
266 out:
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);
272 spin_unlock(&vfsmount_lock);
273 release_mounts(&umount_list);
274 return ret;
278 * return true if the refcount is greater than count
280 static inline int do_refcount_check(struct vfsmount *mnt, int count)
282 int mycount = atomic_read(&mnt->mnt_count) - mnt->mnt_ghosts;
283 return (mycount > count);
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.
294 int propagate_mount_busy(struct vfsmount *mnt, int refcnt)
296 struct vfsmount *m, *child;
297 struct vfsmount *parent = mnt->mnt_parent;
298 int ret = 0;
300 if (mnt == parent)
301 return do_refcount_check(mnt, refcnt);
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
308 if (!list_empty(&mnt->mnt_mounts) || do_refcount_check(mnt, refcnt))
309 return 1;
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;
318 return ret;
322 * NOTE: unmounting 'mnt' naturally propagates to all other mounts its
323 * parent propagates to.
325 static void __propagate_umount(struct vfsmount *mnt)
327 struct vfsmount *parent = mnt->mnt_parent;
328 struct vfsmount *m;
330 BUG_ON(parent == mnt);
332 for (m = propagation_next(parent, parent); m;
333 m = propagation_next(m, parent)) {
335 struct vfsmount *child = __lookup_mnt(m,
336 mnt->mnt_mountpoint, 0);
338 * umount the child only if the child has no
339 * other children
341 if (child && list_empty(&child->mnt_mounts))
342 list_move_tail(&child->mnt_hash, &mnt->mnt_hash);
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.
351 int propagate_umount(struct list_head *list)
353 struct vfsmount *mnt;
355 list_for_each_entry(mnt, list, mnt_hash)
356 __propagate_umount(mnt);
357 return 0;