1 /* 2 * Directory notifications for Linux. 3 * 4 * Copyright (C) 2000,2001,2002 Stephen Rothwell 5 * 6 * Copyright (C) 2009 Eric Paris <Red Hat Inc> 7 * dnotify was largly rewritten to use the new fsnotify infrastructure 8 * 9 * This program is free software; you can redistribute it and/or modify it 10 * under the terms of the GNU General Public License as published by the 11 * Free Software Foundation; either version 2, or (at your option) any 12 * later version. 13 * 14 * This program is distributed in the hope that it will be useful, but 15 * WITHOUT ANY WARRANTY; without even the implied warranty of 16 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU 17 * General Public License for more details. 18 */ 19 #include <linux/fs.h> 20 #include <linux/module.h> 21 #include <linux/sched.h> 22 #include <linux/dnotify.h> 23 #include <linux/init.h> 24 #include <linux/spinlock.h> 25 #include <linux/slab.h> 26 #include <linux/fdtable.h> 27 #include <linux/fsnotify_backend.h> 28 29 int dir_notify_enable __read_mostly = 1; 30 31 static struct kmem_cache *dnotify_struct_cache __read_mostly; 32 static struct kmem_cache *dnotify_mark_cache __read_mostly; 33 static struct fsnotify_group *dnotify_group __read_mostly; 34 35 /* 36 * dnotify will attach one of these to each inode (i_fsnotify_marks) which 37 * is being watched by dnotify. If multiple userspace applications are watching 38 * the same directory with dnotify their information is chained in dn 39 */ 40 struct dnotify_mark { 41 struct fsnotify_mark fsn_mark; 42 struct dnotify_struct *dn; 43 }; 44 45 /* 46 * When a process starts or stops watching an inode the set of events which 47 * dnotify cares about for that inode may change. This function runs the 48 * list of everything receiving dnotify events about this directory and calculates 49 * the set of all those events. After it updates what dnotify is interested in 50 * it calls the fsnotify function so it can update the set of all events relevant 51 * to this inode. 52 */ 53 static void dnotify_recalc_inode_mask(struct fsnotify_mark *fsn_mark) 54 { 55 __u32 new_mask, old_mask; 56 struct dnotify_struct *dn; 57 struct dnotify_mark *dn_mark = container_of(fsn_mark, 58 struct dnotify_mark, 59 fsn_mark); 60 61 assert_spin_locked(&fsn_mark->lock); 62 63 old_mask = fsn_mark->mask; 64 new_mask = 0; 65 for (dn = dn_mark->dn; dn != NULL; dn = dn->dn_next) 66 new_mask |= (dn->dn_mask & ~FS_DN_MULTISHOT); 67 fsnotify_set_mark_mask_locked(fsn_mark, new_mask); 68 69 if (old_mask == new_mask) 70 return; 71 72 if (fsn_mark->inode) 73 fsnotify_recalc_inode_mask(fsn_mark->inode); 74 } 75 76 /* 77 * Mains fsnotify call where events are delivered to dnotify. 78 * Find the dnotify mark on the relevant inode, run the list of dnotify structs 79 * on that mark and determine which of them has expressed interest in receiving 80 * events of this type. When found send the correct process and signal and 81 * destroy the dnotify struct if it was not registered to receive multiple 82 * events. 83 */ 84 static int dnotify_handle_event(struct fsnotify_group *group, 85 struct inode *inode, 86 struct fsnotify_mark *inode_mark, 87 struct fsnotify_mark *vfsmount_mark, 88 u32 mask, const void *data, int data_type, 89 const unsigned char *file_name, u32 cookie) 90 { 91 struct dnotify_mark *dn_mark; 92 struct dnotify_struct *dn; 93 struct dnotify_struct **prev; 94 struct fown_struct *fown; 95 __u32 test_mask = mask & ~FS_EVENT_ON_CHILD; 96 97 /* not a dir, dnotify doesn't care */ 98 if (!S_ISDIR(inode->i_mode)) 99 return 0; 100 101 BUG_ON(vfsmount_mark); 102 103 dn_mark = container_of(inode_mark, struct dnotify_mark, fsn_mark); 104 105 spin_lock(&inode_mark->lock); 106 prev = &dn_mark->dn; 107 while ((dn = *prev) != NULL) { 108 if ((dn->dn_mask & test_mask) == 0) { 109 prev = &dn->dn_next; 110 continue; 111 } 112 fown = &dn->dn_filp->f_owner; 113 send_sigio(fown, dn->dn_fd, POLL_MSG); 114 if (dn->dn_mask & FS_DN_MULTISHOT) 115 prev = &dn->dn_next; 116 else { 117 *prev = dn->dn_next; 118 kmem_cache_free(dnotify_struct_cache, dn); 119 dnotify_recalc_inode_mask(inode_mark); 120 } 121 } 122 123 spin_unlock(&inode_mark->lock); 124 125 return 0; 126 } 127 128 static void dnotify_free_mark(struct fsnotify_mark *fsn_mark) 129 { 130 struct dnotify_mark *dn_mark = container_of(fsn_mark, 131 struct dnotify_mark, 132 fsn_mark); 133 134 BUG_ON(dn_mark->dn); 135 136 kmem_cache_free(dnotify_mark_cache, dn_mark); 137 } 138 139 static struct fsnotify_ops dnotify_fsnotify_ops = { 140 .handle_event = dnotify_handle_event, 141 }; 142 143 /* 144 * Called every time a file is closed. Looks first for a dnotify mark on the 145 * inode. If one is found run all of the ->dn structures attached to that 146 * mark for one relevant to this process closing the file and remove that 147 * dnotify_struct. If that was the last dnotify_struct also remove the 148 * fsnotify_mark. 149 */ 150 void dnotify_flush(struct file *filp, fl_owner_t id) 151 { 152 struct fsnotify_mark *fsn_mark; 153 struct dnotify_mark *dn_mark; 154 struct dnotify_struct *dn; 155 struct dnotify_struct **prev; 156 struct inode *inode; 157 bool free = false; 158 159 inode = file_inode(filp); 160 if (!S_ISDIR(inode->i_mode)) 161 return; 162 163 fsn_mark = fsnotify_find_inode_mark(dnotify_group, inode); 164 if (!fsn_mark) 165 return; 166 dn_mark = container_of(fsn_mark, struct dnotify_mark, fsn_mark); 167 168 mutex_lock(&dnotify_group->mark_mutex); 169 170 spin_lock(&fsn_mark->lock); 171 prev = &dn_mark->dn; 172 while ((dn = *prev) != NULL) { 173 if ((dn->dn_owner == id) && (dn->dn_filp == filp)) { 174 *prev = dn->dn_next; 175 kmem_cache_free(dnotify_struct_cache, dn); 176 dnotify_recalc_inode_mask(fsn_mark); 177 break; 178 } 179 prev = &dn->dn_next; 180 } 181 182 spin_unlock(&fsn_mark->lock); 183 184 /* nothing else could have found us thanks to the dnotify_groups 185 mark_mutex */ 186 if (dn_mark->dn == NULL) { 187 fsnotify_detach_mark(fsn_mark); 188 free = true; 189 } 190 191 mutex_unlock(&dnotify_group->mark_mutex); 192 193 if (free) 194 fsnotify_free_mark(fsn_mark); 195 fsnotify_put_mark(fsn_mark); 196 } 197 198 /* this conversion is done only at watch creation */ 199 static __u32 convert_arg(unsigned long arg) 200 { 201 __u32 new_mask = FS_EVENT_ON_CHILD; 202 203 if (arg & DN_MULTISHOT) 204 new_mask |= FS_DN_MULTISHOT; 205 if (arg & DN_DELETE) 206 new_mask |= (FS_DELETE | FS_MOVED_FROM); 207 if (arg & DN_MODIFY) 208 new_mask |= FS_MODIFY; 209 if (arg & DN_ACCESS) 210 new_mask |= FS_ACCESS; 211 if (arg & DN_ATTRIB) 212 new_mask |= FS_ATTRIB; 213 if (arg & DN_RENAME) 214 new_mask |= FS_DN_RENAME; 215 if (arg & DN_CREATE) 216 new_mask |= (FS_CREATE | FS_MOVED_TO); 217 218 return new_mask; 219 } 220 221 /* 222 * If multiple processes watch the same inode with dnotify there is only one 223 * dnotify mark in inode->i_fsnotify_marks but we chain a dnotify_struct 224 * onto that mark. This function either attaches the new dnotify_struct onto 225 * that list, or it |= the mask onto an existing dnofiy_struct. 226 */ 227 static int attach_dn(struct dnotify_struct *dn, struct dnotify_mark *dn_mark, 228 fl_owner_t id, int fd, struct file *filp, __u32 mask) 229 { 230 struct dnotify_struct *odn; 231 232 odn = dn_mark->dn; 233 while (odn != NULL) { 234 /* adding more events to existing dnofiy_struct? */ 235 if ((odn->dn_owner == id) && (odn->dn_filp == filp)) { 236 odn->dn_fd = fd; 237 odn->dn_mask |= mask; 238 return -EEXIST; 239 } 240 odn = odn->dn_next; 241 } 242 243 dn->dn_mask = mask; 244 dn->dn_fd = fd; 245 dn->dn_filp = filp; 246 dn->dn_owner = id; 247 dn->dn_next = dn_mark->dn; 248 dn_mark->dn = dn; 249 250 return 0; 251 } 252 253 /* 254 * When a process calls fcntl to attach a dnotify watch to a directory it ends 255 * up here. Allocate both a mark for fsnotify to add and a dnotify_struct to be 256 * attached to the fsnotify_mark. 257 */ 258 int fcntl_dirnotify(int fd, struct file *filp, unsigned long arg) 259 { 260 struct dnotify_mark *new_dn_mark, *dn_mark; 261 struct fsnotify_mark *new_fsn_mark, *fsn_mark; 262 struct dnotify_struct *dn; 263 struct inode *inode; 264 fl_owner_t id = current->files; 265 struct file *f; 266 int destroy = 0, error = 0; 267 __u32 mask; 268 269 /* we use these to tell if we need to kfree */ 270 new_fsn_mark = NULL; 271 dn = NULL; 272 273 if (!dir_notify_enable) { 274 error = -EINVAL; 275 goto out_err; 276 } 277 278 /* a 0 mask means we are explicitly removing the watch */ 279 if ((arg & ~DN_MULTISHOT) == 0) { 280 dnotify_flush(filp, id); 281 error = 0; 282 goto out_err; 283 } 284 285 /* dnotify only works on directories */ 286 inode = file_inode(filp); 287 if (!S_ISDIR(inode->i_mode)) { 288 error = -ENOTDIR; 289 goto out_err; 290 } 291 292 /* expect most fcntl to add new rather than augment old */ 293 dn = kmem_cache_alloc(dnotify_struct_cache, GFP_KERNEL); 294 if (!dn) { 295 error = -ENOMEM; 296 goto out_err; 297 } 298 299 /* new fsnotify mark, we expect most fcntl calls to add a new mark */ 300 new_dn_mark = kmem_cache_alloc(dnotify_mark_cache, GFP_KERNEL); 301 if (!new_dn_mark) { 302 error = -ENOMEM; 303 goto out_err; 304 } 305 306 /* convert the userspace DN_* "arg" to the internal FS_* defines in fsnotify */ 307 mask = convert_arg(arg); 308 309 /* set up the new_fsn_mark and new_dn_mark */ 310 new_fsn_mark = &new_dn_mark->fsn_mark; 311 fsnotify_init_mark(new_fsn_mark, dnotify_free_mark); 312 new_fsn_mark->mask = mask; 313 new_dn_mark->dn = NULL; 314 315 /* this is needed to prevent the fcntl/close race described below */ 316 mutex_lock(&dnotify_group->mark_mutex); 317 318 /* add the new_fsn_mark or find an old one. */ 319 fsn_mark = fsnotify_find_inode_mark(dnotify_group, inode); 320 if (fsn_mark) { 321 dn_mark = container_of(fsn_mark, struct dnotify_mark, fsn_mark); 322 spin_lock(&fsn_mark->lock); 323 } else { 324 fsnotify_add_mark_locked(new_fsn_mark, dnotify_group, inode, 325 NULL, 0); 326 spin_lock(&new_fsn_mark->lock); 327 fsn_mark = new_fsn_mark; 328 dn_mark = new_dn_mark; 329 /* we used new_fsn_mark, so don't free it */ 330 new_fsn_mark = NULL; 331 } 332 333 rcu_read_lock(); 334 f = fcheck(fd); 335 rcu_read_unlock(); 336 337 /* if (f != filp) means that we lost a race and another task/thread 338 * actually closed the fd we are still playing with before we grabbed 339 * the dnotify_groups mark_mutex and fsn_mark->lock. Since closing the 340 * fd is the only time we clean up the marks we need to get our mark 341 * off the list. */ 342 if (f != filp) { 343 /* if we added ourselves, shoot ourselves, it's possible that 344 * the flush actually did shoot this fsn_mark. That's fine too 345 * since multiple calls to destroy_mark is perfectly safe, if 346 * we found a dn_mark already attached to the inode, just sod 347 * off silently as the flush at close time dealt with it. 348 */ 349 if (dn_mark == new_dn_mark) 350 destroy = 1; 351 goto out; 352 } 353 354 __f_setown(filp, task_pid(current), PIDTYPE_PID, 0); 355 356 error = attach_dn(dn, dn_mark, id, fd, filp, mask); 357 /* !error means that we attached the dn to the dn_mark, so don't free it */ 358 if (!error) 359 dn = NULL; 360 /* -EEXIST means that we didn't add this new dn and used an old one. 361 * that isn't an error (and the unused dn should be freed) */ 362 else if (error == -EEXIST) 363 error = 0; 364 365 dnotify_recalc_inode_mask(fsn_mark); 366 out: 367 spin_unlock(&fsn_mark->lock); 368 369 if (destroy) 370 fsnotify_detach_mark(fsn_mark); 371 mutex_unlock(&dnotify_group->mark_mutex); 372 if (destroy) 373 fsnotify_free_mark(fsn_mark); 374 fsnotify_put_mark(fsn_mark); 375 out_err: 376 if (new_fsn_mark) 377 fsnotify_put_mark(new_fsn_mark); 378 if (dn) 379 kmem_cache_free(dnotify_struct_cache, dn); 380 return error; 381 } 382 383 static int __init dnotify_init(void) 384 { 385 dnotify_struct_cache = KMEM_CACHE(dnotify_struct, SLAB_PANIC); 386 dnotify_mark_cache = KMEM_CACHE(dnotify_mark, SLAB_PANIC); 387 388 dnotify_group = fsnotify_alloc_group(&dnotify_fsnotify_ops); 389 if (IS_ERR(dnotify_group)) 390 panic("unable to allocate fsnotify group for dnotify\n"); 391 return 0; 392 } 393 394 module_init(dnotify_init) 395