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 "pnode.h" 13 14 /* return the next shared peer mount of @p */ 15 static inline struct vfsmount *next_peer(struct vfsmount *p) 16 { 17 return list_entry(p->mnt_share.next, struct vfsmount, mnt_share); 18 } 19 20 static inline struct vfsmount *first_slave(struct vfsmount *p) 21 { 22 return list_entry(p->mnt_slave_list.next, struct vfsmount, mnt_slave); 23 } 24 25 static inline struct vfsmount *next_slave(struct vfsmount *p) 26 { 27 return list_entry(p->mnt_slave.next, struct vfsmount, mnt_slave); 28 } 29 30 static int do_make_slave(struct vfsmount *mnt) 31 { 32 struct vfsmount *peer_mnt = mnt, *master = mnt->mnt_master; 33 struct vfsmount *slave_mnt; 34 35 /* 36 * slave 'mnt' to a peer mount that has the 37 * same root dentry. If none is available than 38 * slave it to anything that is available. 39 */ 40 while ((peer_mnt = next_peer(peer_mnt)) != mnt && 41 peer_mnt->mnt_root != mnt->mnt_root) ; 42 43 if (peer_mnt == mnt) { 44 peer_mnt = next_peer(mnt); 45 if (peer_mnt == mnt) 46 peer_mnt = NULL; 47 } 48 list_del_init(&mnt->mnt_share); 49 50 if (peer_mnt) 51 master = peer_mnt; 52 53 if (master) { 54 list_for_each_entry(slave_mnt, &mnt->mnt_slave_list, mnt_slave) 55 slave_mnt->mnt_master = master; 56 list_move(&mnt->mnt_slave, &master->mnt_slave_list); 57 list_splice(&mnt->mnt_slave_list, master->mnt_slave_list.prev); 58 INIT_LIST_HEAD(&mnt->mnt_slave_list); 59 } else { 60 struct list_head *p = &mnt->mnt_slave_list; 61 while (!list_empty(p)) { 62 slave_mnt = list_first_entry(p, 63 struct vfsmount, mnt_slave); 64 list_del_init(&slave_mnt->mnt_slave); 65 slave_mnt->mnt_master = NULL; 66 } 67 } 68 mnt->mnt_master = master; 69 CLEAR_MNT_SHARED(mnt); 70 INIT_LIST_HEAD(&mnt->mnt_slave_list); 71 return 0; 72 } 73 74 void change_mnt_propagation(struct vfsmount *mnt, int type) 75 { 76 if (type == MS_SHARED) { 77 set_mnt_shared(mnt); 78 return; 79 } 80 do_make_slave(mnt); 81 if (type != MS_SLAVE) { 82 list_del_init(&mnt->mnt_slave); 83 mnt->mnt_master = NULL; 84 if (type == MS_UNBINDABLE) 85 mnt->mnt_flags |= MNT_UNBINDABLE; 86 } 87 } 88 89 /* 90 * get the next mount in the propagation tree. 91 * @m: the mount seen last 92 * @origin: the original mount from where the tree walk initiated 93 */ 94 static struct vfsmount *propagation_next(struct vfsmount *m, 95 struct vfsmount *origin) 96 { 97 /* are there any slaves of this mount? */ 98 if (!IS_MNT_NEW(m) && !list_empty(&m->mnt_slave_list)) 99 return first_slave(m); 100 101 while (1) { 102 struct vfsmount *next; 103 struct vfsmount *master = m->mnt_master; 104 105 if (master == origin->mnt_master) { 106 next = next_peer(m); 107 return ((next == origin) ? NULL : next); 108 } else if (m->mnt_slave.next != &master->mnt_slave_list) 109 return next_slave(m); 110 111 /* back at master */ 112 m = master; 113 } 114 } 115 116 /* 117 * return the source mount to be used for cloning 118 * 119 * @dest the current destination mount 120 * @last_dest the last seen destination mount 121 * @last_src the last seen source mount 122 * @type return CL_SLAVE if the new mount has to be 123 * cloned as a slave. 124 */ 125 static struct vfsmount *get_source(struct vfsmount *dest, 126 struct vfsmount *last_dest, 127 struct vfsmount *last_src, 128 int *type) 129 { 130 struct vfsmount *p_last_src = NULL; 131 struct vfsmount *p_last_dest = NULL; 132 *type = CL_PROPAGATION; 133 134 if (IS_MNT_SHARED(dest)) 135 *type |= CL_MAKE_SHARED; 136 137 while (last_dest != dest->mnt_master) { 138 p_last_dest = last_dest; 139 p_last_src = last_src; 140 last_dest = last_dest->mnt_master; 141 last_src = last_src->mnt_master; 142 } 143 144 if (p_last_dest) { 145 do { 146 p_last_dest = next_peer(p_last_dest); 147 } while (IS_MNT_NEW(p_last_dest)); 148 } 149 150 if (dest != p_last_dest) { 151 *type |= CL_SLAVE; 152 return last_src; 153 } else 154 return p_last_src; 155 } 156 157 /* 158 * mount 'source_mnt' under the destination 'dest_mnt' at 159 * dentry 'dest_dentry'. And propagate that mount to 160 * all the peer and slave mounts of 'dest_mnt'. 161 * Link all the new mounts into a propagation tree headed at 162 * source_mnt. Also link all the new mounts using ->mnt_list 163 * headed at source_mnt's ->mnt_list 164 * 165 * @dest_mnt: destination mount. 166 * @dest_dentry: destination dentry. 167 * @source_mnt: source mount. 168 * @tree_list : list of heads of trees to be attached. 169 */ 170 int propagate_mnt(struct vfsmount *dest_mnt, struct dentry *dest_dentry, 171 struct vfsmount *source_mnt, struct list_head *tree_list) 172 { 173 struct vfsmount *m, *child; 174 int ret = 0; 175 struct vfsmount *prev_dest_mnt = dest_mnt; 176 struct vfsmount *prev_src_mnt = source_mnt; 177 LIST_HEAD(tmp_list); 178 LIST_HEAD(umount_list); 179 180 for (m = propagation_next(dest_mnt, dest_mnt); m; 181 m = propagation_next(m, dest_mnt)) { 182 int type; 183 struct vfsmount *source; 184 185 if (IS_MNT_NEW(m)) 186 continue; 187 188 source = get_source(m, prev_dest_mnt, prev_src_mnt, &type); 189 190 if (!(child = copy_tree(source, source->mnt_root, type))) { 191 ret = -ENOMEM; 192 list_splice(tree_list, tmp_list.prev); 193 goto out; 194 } 195 196 if (is_subdir(dest_dentry, m->mnt_root)) { 197 mnt_set_mountpoint(m, dest_dentry, child); 198 list_add_tail(&child->mnt_hash, tree_list); 199 } else { 200 /* 201 * This can happen if the parent mount was bind mounted 202 * on some subdirectory of a shared/slave mount. 203 */ 204 list_add_tail(&child->mnt_hash, &tmp_list); 205 } 206 prev_dest_mnt = m; 207 prev_src_mnt = child; 208 } 209 out: 210 spin_lock(&vfsmount_lock); 211 while (!list_empty(&tmp_list)) { 212 child = list_entry(tmp_list.next, struct vfsmount, mnt_hash); 213 list_del_init(&child->mnt_hash); 214 umount_tree(child, 0, &umount_list); 215 } 216 spin_unlock(&vfsmount_lock); 217 release_mounts(&umount_list); 218 return ret; 219 } 220 221 /* 222 * return true if the refcount is greater than count 223 */ 224 static inline int do_refcount_check(struct vfsmount *mnt, int count) 225 { 226 int mycount = atomic_read(&mnt->mnt_count); 227 return (mycount > count); 228 } 229 230 /* 231 * check if the mount 'mnt' can be unmounted successfully. 232 * @mnt: the mount to be checked for unmount 233 * NOTE: unmounting 'mnt' would naturally propagate to all 234 * other mounts its parent propagates to. 235 * Check if any of these mounts that **do not have submounts** 236 * have more references than 'refcnt'. If so return busy. 237 */ 238 int propagate_mount_busy(struct vfsmount *mnt, int refcnt) 239 { 240 struct vfsmount *m, *child; 241 struct vfsmount *parent = mnt->mnt_parent; 242 int ret = 0; 243 244 if (mnt == parent) 245 return do_refcount_check(mnt, refcnt); 246 247 /* 248 * quickly check if the current mount can be unmounted. 249 * If not, we don't have to go checking for all other 250 * mounts 251 */ 252 if (!list_empty(&mnt->mnt_mounts) || do_refcount_check(mnt, refcnt)) 253 return 1; 254 255 for (m = propagation_next(parent, parent); m; 256 m = propagation_next(m, parent)) { 257 child = __lookup_mnt(m, mnt->mnt_mountpoint, 0); 258 if (child && list_empty(&child->mnt_mounts) && 259 (ret = do_refcount_check(child, 1))) 260 break; 261 } 262 return ret; 263 } 264 265 /* 266 * NOTE: unmounting 'mnt' naturally propagates to all other mounts its 267 * parent propagates to. 268 */ 269 static void __propagate_umount(struct vfsmount *mnt) 270 { 271 struct vfsmount *parent = mnt->mnt_parent; 272 struct vfsmount *m; 273 274 BUG_ON(parent == mnt); 275 276 for (m = propagation_next(parent, parent); m; 277 m = propagation_next(m, parent)) { 278 279 struct vfsmount *child = __lookup_mnt(m, 280 mnt->mnt_mountpoint, 0); 281 /* 282 * umount the child only if the child has no 283 * other children 284 */ 285 if (child && list_empty(&child->mnt_mounts)) 286 list_move_tail(&child->mnt_hash, &mnt->mnt_hash); 287 } 288 } 289 290 /* 291 * collect all mounts that receive propagation from the mount in @list, 292 * and return these additional mounts in the same list. 293 * @list: the list of mounts to be unmounted. 294 */ 295 int propagate_umount(struct list_head *list) 296 { 297 struct vfsmount *mnt; 298 299 list_for_each_entry(mnt, list, mnt_hash) 300 __propagate_umount(mnt); 301 return 0; 302 } 303