| 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 */ |
| 16 | static inline struct vfsmount *next_peer(struct vfsmount *p) |
| 17 | { |
| 18 | return list_entry(p->mnt_share.next, struct vfsmount, mnt_share); |
| 19 | } |
| 20 | |
| 21 | static inline struct vfsmount *first_slave(struct vfsmount *p) |
| 22 | { |
| 23 | return list_entry(p->mnt_slave_list.next, struct vfsmount, mnt_slave); |
| 24 | } |
| 25 | |
| 26 | static 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 | */ |
| 36 | static 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 | |
| 46 | static 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 | */ |
| 69 | int 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 | |
| 82 | static 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 | |
| 129 | /* |
| 130 | * vfsmount lock must be held for write |
| 131 | */ |
| 132 | void change_mnt_propagation(struct vfsmount *mnt, int type) |
| 133 | { |
| 134 | if (type == MS_SHARED) { |
| 135 | set_mnt_shared(mnt); |
| 136 | return; |
| 137 | } |
| 138 | do_make_slave(mnt); |
| 139 | if (type != MS_SLAVE) { |
| 140 | list_del_init(&mnt->mnt_slave); |
| 141 | mnt->mnt_master = NULL; |
| 142 | if (type == MS_UNBINDABLE) |
| 143 | mnt->mnt_flags |= MNT_UNBINDABLE; |
| 144 | else |
| 145 | mnt->mnt_flags &= ~MNT_UNBINDABLE; |
| 146 | } |
| 147 | } |
| 148 | |
| 149 | /* |
| 150 | * get the next mount in the propagation tree. |
| 151 | * @m: the mount seen last |
| 152 | * @origin: the original mount from where the tree walk initiated |
| 153 | * |
| 154 | * Note that peer groups form contiguous segments of slave lists. |
| 155 | * We rely on that in get_source() to be able to find out if |
| 156 | * vfsmount found while iterating with propagation_next() is |
| 157 | * a peer of one we'd found earlier. |
| 158 | */ |
| 159 | static struct vfsmount *propagation_next(struct vfsmount *m, |
| 160 | struct vfsmount *origin) |
| 161 | { |
| 162 | /* are there any slaves of this mount? */ |
| 163 | if (!IS_MNT_NEW(m) && !list_empty(&m->mnt_slave_list)) |
| 164 | return first_slave(m); |
| 165 | |
| 166 | while (1) { |
| 167 | struct vfsmount *next; |
| 168 | struct vfsmount *master = m->mnt_master; |
| 169 | |
| 170 | if (master == origin->mnt_master) { |
| 171 | next = next_peer(m); |
| 172 | return ((next == origin) ? NULL : next); |
| 173 | } else if (m->mnt_slave.next != &master->mnt_slave_list) |
| 174 | return next_slave(m); |
| 175 | |
| 176 | /* back at master */ |
| 177 | m = master; |
| 178 | } |
| 179 | } |
| 180 | |
| 181 | /* |
| 182 | * return the source mount to be used for cloning |
| 183 | * |
| 184 | * @dest the current destination mount |
| 185 | * @last_dest the last seen destination mount |
| 186 | * @last_src the last seen source mount |
| 187 | * @type return CL_SLAVE if the new mount has to be |
| 188 | * cloned as a slave. |
| 189 | */ |
| 190 | static struct vfsmount *get_source(struct vfsmount *dest, |
| 191 | struct vfsmount *last_dest, |
| 192 | struct vfsmount *last_src, |
| 193 | int *type) |
| 194 | { |
| 195 | struct vfsmount *p_last_src = NULL; |
| 196 | struct vfsmount *p_last_dest = NULL; |
| 197 | |
| 198 | while (last_dest != dest->mnt_master) { |
| 199 | p_last_dest = last_dest; |
| 200 | p_last_src = last_src; |
| 201 | last_dest = last_dest->mnt_master; |
| 202 | last_src = last_src->mnt_master; |
| 203 | } |
| 204 | |
| 205 | if (p_last_dest) { |
| 206 | do { |
| 207 | p_last_dest = next_peer(p_last_dest); |
| 208 | } while (IS_MNT_NEW(p_last_dest)); |
| 209 | /* is that a peer of the earlier? */ |
| 210 | if (dest == p_last_dest) { |
| 211 | *type = CL_MAKE_SHARED; |
| 212 | return p_last_src; |
| 213 | } |
| 214 | } |
| 215 | /* slave of the earlier, then */ |
| 216 | *type = CL_SLAVE; |
| 217 | /* beginning of peer group among the slaves? */ |
| 218 | if (IS_MNT_SHARED(dest)) |
| 219 | *type |= CL_MAKE_SHARED; |
| 220 | return last_src; |
| 221 | } |
| 222 | |
| 223 | /* |
| 224 | * mount 'source_mnt' under the destination 'dest_mnt' at |
| 225 | * dentry 'dest_dentry'. And propagate that mount to |
| 226 | * all the peer and slave mounts of 'dest_mnt'. |
| 227 | * Link all the new mounts into a propagation tree headed at |
| 228 | * source_mnt. Also link all the new mounts using ->mnt_list |
| 229 | * headed at source_mnt's ->mnt_list |
| 230 | * |
| 231 | * @dest_mnt: destination mount. |
| 232 | * @dest_dentry: destination dentry. |
| 233 | * @source_mnt: source mount. |
| 234 | * @tree_list : list of heads of trees to be attached. |
| 235 | */ |
| 236 | int propagate_mnt(struct vfsmount *dest_mnt, struct dentry *dest_dentry, |
| 237 | struct vfsmount *source_mnt, struct list_head *tree_list) |
| 238 | { |
| 239 | struct vfsmount *m, *child; |
| 240 | int ret = 0; |
| 241 | struct vfsmount *prev_dest_mnt = dest_mnt; |
| 242 | struct vfsmount *prev_src_mnt = source_mnt; |
| 243 | LIST_HEAD(tmp_list); |
| 244 | LIST_HEAD(umount_list); |
| 245 | |
| 246 | for (m = propagation_next(dest_mnt, dest_mnt); m; |
| 247 | m = propagation_next(m, dest_mnt)) { |
| 248 | int type; |
| 249 | struct vfsmount *source; |
| 250 | |
| 251 | if (IS_MNT_NEW(m)) |
| 252 | continue; |
| 253 | |
| 254 | source = get_source(m, prev_dest_mnt, prev_src_mnt, &type); |
| 255 | |
| 256 | if (!(child = copy_tree(source, source->mnt_root, type))) { |
| 257 | ret = -ENOMEM; |
| 258 | list_splice(tree_list, tmp_list.prev); |
| 259 | goto out; |
| 260 | } |
| 261 | |
| 262 | if (is_subdir(dest_dentry, m->mnt_root)) { |
| 263 | mnt_set_mountpoint(m, dest_dentry, child); |
| 264 | list_add_tail(&child->mnt_hash, tree_list); |
| 265 | } else { |
| 266 | /* |
| 267 | * This can happen if the parent mount was bind mounted |
| 268 | * on some subdirectory of a shared/slave mount. |
| 269 | */ |
| 270 | list_add_tail(&child->mnt_hash, &tmp_list); |
| 271 | } |
| 272 | prev_dest_mnt = m; |
| 273 | prev_src_mnt = child; |
| 274 | } |
| 275 | out: |
| 276 | br_write_lock(vfsmount_lock); |
| 277 | while (!list_empty(&tmp_list)) { |
| 278 | child = list_first_entry(&tmp_list, struct vfsmount, mnt_hash); |
| 279 | umount_tree(child, 0, &umount_list); |
| 280 | } |
| 281 | br_write_unlock(vfsmount_lock); |
| 282 | release_mounts(&umount_list); |
| 283 | return ret; |
| 284 | } |
| 285 | |
| 286 | /* |
| 287 | * return true if the refcount is greater than count |
| 288 | */ |
| 289 | static inline int do_refcount_check(struct vfsmount *mnt, int count) |
| 290 | { |
| 291 | int mycount = mnt_get_count(mnt) - mnt->mnt_ghosts; |
| 292 | return (mycount > count); |
| 293 | } |
| 294 | |
| 295 | /* |
| 296 | * check if the mount 'mnt' can be unmounted successfully. |
| 297 | * @mnt: the mount to be checked for unmount |
| 298 | * NOTE: unmounting 'mnt' would naturally propagate to all |
| 299 | * other mounts its parent propagates to. |
| 300 | * Check if any of these mounts that **do not have submounts** |
| 301 | * have more references than 'refcnt'. If so return busy. |
| 302 | * |
| 303 | * vfsmount lock must be held for write |
| 304 | */ |
| 305 | int propagate_mount_busy(struct vfsmount *mnt, int refcnt) |
| 306 | { |
| 307 | struct vfsmount *m, *child; |
| 308 | struct vfsmount *parent = mnt->mnt_parent; |
| 309 | int ret = 0; |
| 310 | |
| 311 | if (mnt == parent) |
| 312 | return do_refcount_check(mnt, refcnt); |
| 313 | |
| 314 | /* |
| 315 | * quickly check if the current mount can be unmounted. |
| 316 | * If not, we don't have to go checking for all other |
| 317 | * mounts |
| 318 | */ |
| 319 | if (!list_empty(&mnt->mnt_mounts) || do_refcount_check(mnt, refcnt)) |
| 320 | return 1; |
| 321 | |
| 322 | for (m = propagation_next(parent, parent); m; |
| 323 | m = propagation_next(m, parent)) { |
| 324 | child = __lookup_mnt(m, mnt->mnt_mountpoint, 0); |
| 325 | if (child && list_empty(&child->mnt_mounts) && |
| 326 | (ret = do_refcount_check(child, 1))) |
| 327 | break; |
| 328 | } |
| 329 | return ret; |
| 330 | } |
| 331 | |
| 332 | /* |
| 333 | * NOTE: unmounting 'mnt' naturally propagates to all other mounts its |
| 334 | * parent propagates to. |
| 335 | */ |
| 336 | static void __propagate_umount(struct vfsmount *mnt) |
| 337 | { |
| 338 | struct vfsmount *parent = mnt->mnt_parent; |
| 339 | struct vfsmount *m; |
| 340 | |
| 341 | BUG_ON(parent == mnt); |
| 342 | |
| 343 | for (m = propagation_next(parent, parent); m; |
| 344 | m = propagation_next(m, parent)) { |
| 345 | |
| 346 | struct vfsmount *child = __lookup_mnt(m, |
| 347 | mnt->mnt_mountpoint, 0); |
| 348 | /* |
| 349 | * umount the child only if the child has no |
| 350 | * other children |
| 351 | */ |
| 352 | if (child && list_empty(&child->mnt_mounts)) |
| 353 | list_move_tail(&child->mnt_hash, &mnt->mnt_hash); |
| 354 | } |
| 355 | } |
| 356 | |
| 357 | /* |
| 358 | * collect all mounts that receive propagation from the mount in @list, |
| 359 | * and return these additional mounts in the same list. |
| 360 | * @list: the list of mounts to be unmounted. |
| 361 | * |
| 362 | * vfsmount lock must be held for write |
| 363 | */ |
| 364 | int propagate_umount(struct list_head *list) |
| 365 | { |
| 366 | struct vfsmount *mnt; |
| 367 | |
| 368 | list_for_each_entry(mnt, list, mnt_hash) |
| 369 | __propagate_umount(mnt); |
| 370 | return 0; |
| 371 | } |