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 29int dir_notify_enable __read_mostly = 1; 30 31static struct kmem_cache *dnotify_struct_cache __read_mostly; 32static struct kmem_cache *dnotify_mark_cache __read_mostly; 33static struct fsnotify_group *dnotify_group __read_mostly; 34static DEFINE_MUTEX(dnotify_mark_mutex); 35 36/* 37 * dnotify will attach one of these to each inode (i_fsnotify_marks) which 38 * is being watched by dnotify. If multiple userspace applications are watching 39 * the same directory with dnotify their information is chained in dn 40 */ 41struct dnotify_mark { 42 struct fsnotify_mark fsn_mark; 43 struct dnotify_struct *dn; 44}; 45 46/* 47 * When a process starts or stops watching an inode the set of events which 48 * dnotify cares about for that inode may change. This function runs the 49 * list of everything receiving dnotify events about this directory and calculates 50 * the set of all those events. After it updates what dnotify is interested in 51 * it calls the fsnotify function so it can update the set of all events relevant 52 * to this inode. 53 */ 54static void dnotify_recalc_inode_mask(struct fsnotify_mark *fsn_mark) 55{ 56 __u32 new_mask, old_mask; 57 struct dnotify_struct *dn; 58 struct dnotify_mark *dn_mark = container_of(fsn_mark, 59 struct dnotify_mark, 60 fsn_mark); 61 62 assert_spin_locked(&fsn_mark->lock); 63 64 old_mask = fsn_mark->mask; 65 new_mask = 0; 66 for (dn = dn_mark->dn; dn != NULL; dn = dn->dn_next) 67 new_mask |= (dn->dn_mask & ~FS_DN_MULTISHOT); 68 fsnotify_set_mark_mask_locked(fsn_mark, new_mask); 69 70 if (old_mask == new_mask) 71 return; 72 73 if (fsn_mark->i.inode) 74 fsnotify_recalc_inode_mask(fsn_mark->i.inode); 75} 76 77/* 78 * Mains fsnotify call where events are delivered to dnotify. 79 * Find the dnotify mark on the relevant inode, run the list of dnotify structs 80 * on that mark and determine which of them has expressed interest in receiving 81 * events of this type. When found send the correct process and signal and 82 * destroy the dnotify struct if it was not registered to receive multiple 83 * events. 84 */ 85static int dnotify_handle_event(struct fsnotify_group *group, 86 struct fsnotify_mark *inode_mark, 87 struct fsnotify_mark *vfsmount_mark, 88 struct fsnotify_event *event) 89{ 90 struct dnotify_mark *dn_mark; 91 struct inode *to_tell; 92 struct dnotify_struct *dn; 93 struct dnotify_struct **prev; 94 struct fown_struct *fown; 95 __u32 test_mask = event->mask & ~FS_EVENT_ON_CHILD; 96 97 BUG_ON(vfsmount_mark); 98 99 to_tell = event->to_tell; 100 101 dn_mark = container_of(inode_mark, struct dnotify_mark, fsn_mark); 102 103 spin_lock(&inode_mark->lock); 104 prev = &dn_mark->dn; 105 while ((dn = *prev) != NULL) { 106 if ((dn->dn_mask & test_mask) == 0) { 107 prev = &dn->dn_next; 108 continue; 109 } 110 fown = &dn->dn_filp->f_owner; 111 send_sigio(fown, dn->dn_fd, POLL_MSG); 112 if (dn->dn_mask & FS_DN_MULTISHOT) 113 prev = &dn->dn_next; 114 else { 115 *prev = dn->dn_next; 116 kmem_cache_free(dnotify_struct_cache, dn); 117 dnotify_recalc_inode_mask(inode_mark); 118 } 119 } 120 121 spin_unlock(&inode_mark->lock); 122 123 return 0; 124} 125 126/* 127 * Given an inode and mask determine if dnotify would be interested in sending 128 * userspace notification for that pair. 129 */ 130static bool dnotify_should_send_event(struct fsnotify_group *group, 131 struct inode *inode, 132 struct fsnotify_mark *inode_mark, 133 struct fsnotify_mark *vfsmount_mark, 134 __u32 mask, void *data, int data_type) 135{ 136 /* not a dir, dnotify doesn't care */ 137 if (!S_ISDIR(inode->i_mode)) 138 return false; 139 140 return true; 141} 142 143static void dnotify_free_mark(struct fsnotify_mark *fsn_mark) 144{ 145 struct dnotify_mark *dn_mark = container_of(fsn_mark, 146 struct dnotify_mark, 147 fsn_mark); 148 149 BUG_ON(dn_mark->dn); 150 151 kmem_cache_free(dnotify_mark_cache, dn_mark); 152} 153 154static struct fsnotify_ops dnotify_fsnotify_ops = { 155 .handle_event = dnotify_handle_event, 156 .should_send_event = dnotify_should_send_event, 157 .free_group_priv = NULL, 158 .freeing_mark = NULL, 159 .free_event_priv = NULL, 160}; 161 162/* 163 * Called every time a file is closed. Looks first for a dnotify mark on the 164 * inode. If one is found run all of the ->dn structures attached to that 165 * mark for one relevant to this process closing the file and remove that 166 * dnotify_struct. If that was the last dnotify_struct also remove the 167 * fsnotify_mark. 168 */ 169void dnotify_flush(struct file *filp, fl_owner_t id) 170{ 171 struct fsnotify_mark *fsn_mark; 172 struct dnotify_mark *dn_mark; 173 struct dnotify_struct *dn; 174 struct dnotify_struct **prev; 175 struct inode *inode; 176 177 inode = filp->f_path.dentry->d_inode; 178 if (!S_ISDIR(inode->i_mode)) 179 return; 180 181 fsn_mark = fsnotify_find_inode_mark(dnotify_group, inode); 182 if (!fsn_mark) 183 return; 184 dn_mark = container_of(fsn_mark, struct dnotify_mark, fsn_mark); 185 186 mutex_lock(&dnotify_mark_mutex); 187 188 spin_lock(&fsn_mark->lock); 189 prev = &dn_mark->dn; 190 while ((dn = *prev) != NULL) { 191 if ((dn->dn_owner == id) && (dn->dn_filp == filp)) { 192 *prev = dn->dn_next; 193 kmem_cache_free(dnotify_struct_cache, dn); 194 dnotify_recalc_inode_mask(fsn_mark); 195 break; 196 } 197 prev = &dn->dn_next; 198 } 199 200 spin_unlock(&fsn_mark->lock); 201 202 /* nothing else could have found us thanks to the dnotify_mark_mutex */ 203 if (dn_mark->dn == NULL) 204 fsnotify_destroy_mark(fsn_mark); 205 206 mutex_unlock(&dnotify_mark_mutex); 207 208 fsnotify_put_mark(fsn_mark); 209} 210 211/* this conversion is done only at watch creation */ 212static __u32 convert_arg(unsigned long arg) 213{ 214 __u32 new_mask = FS_EVENT_ON_CHILD; 215 216 if (arg & DN_MULTISHOT) 217 new_mask |= FS_DN_MULTISHOT; 218 if (arg & DN_DELETE) 219 new_mask |= (FS_DELETE | FS_MOVED_FROM); 220 if (arg & DN_MODIFY) 221 new_mask |= FS_MODIFY; 222 if (arg & DN_ACCESS) 223 new_mask |= FS_ACCESS; 224 if (arg & DN_ATTRIB) 225 new_mask |= FS_ATTRIB; 226 if (arg & DN_RENAME) 227 new_mask |= FS_DN_RENAME; 228 if (arg & DN_CREATE) 229 new_mask |= (FS_CREATE | FS_MOVED_TO); 230 231 return new_mask; 232} 233 234/* 235 * If multiple processes watch the same inode with dnotify there is only one 236 * dnotify mark in inode->i_fsnotify_marks but we chain a dnotify_struct 237 * onto that mark. This function either attaches the new dnotify_struct onto 238 * that list, or it |= the mask onto an existing dnofiy_struct. 239 */ 240static int attach_dn(struct dnotify_struct *dn, struct dnotify_mark *dn_mark, 241 fl_owner_t id, int fd, struct file *filp, __u32 mask) 242{ 243 struct dnotify_struct *odn; 244 245 odn = dn_mark->dn; 246 while (odn != NULL) { 247 /* adding more events to existing dnofiy_struct? */ 248 if ((odn->dn_owner == id) && (odn->dn_filp == filp)) { 249 odn->dn_fd = fd; 250 odn->dn_mask |= mask; 251 return -EEXIST; 252 } 253 odn = odn->dn_next; 254 } 255 256 dn->dn_mask = mask; 257 dn->dn_fd = fd; 258 dn->dn_filp = filp; 259 dn->dn_owner = id; 260 dn->dn_next = dn_mark->dn; 261 dn_mark->dn = dn; 262 263 return 0; 264} 265 266/* 267 * When a process calls fcntl to attach a dnotify watch to a directory it ends 268 * up here. Allocate both a mark for fsnotify to add and a dnotify_struct to be 269 * attached to the fsnotify_mark. 270 */ 271int fcntl_dirnotify(int fd, struct file *filp, unsigned long arg) 272{ 273 struct dnotify_mark *new_dn_mark, *dn_mark; 274 struct fsnotify_mark *new_fsn_mark, *fsn_mark; 275 struct dnotify_struct *dn; 276 struct inode *inode; 277 fl_owner_t id = current->files; 278 struct file *f; 279 int destroy = 0, error = 0; 280 __u32 mask; 281 282 /* we use these to tell if we need to kfree */ 283 new_fsn_mark = NULL; 284 dn = NULL; 285 286 if (!dir_notify_enable) { 287 error = -EINVAL; 288 goto out_err; 289 } 290 291 /* a 0 mask means we are explicitly removing the watch */ 292 if ((arg & ~DN_MULTISHOT) == 0) { 293 dnotify_flush(filp, id); 294 error = 0; 295 goto out_err; 296 } 297 298 /* dnotify only works on directories */ 299 inode = filp->f_path.dentry->d_inode; 300 if (!S_ISDIR(inode->i_mode)) { 301 error = -ENOTDIR; 302 goto out_err; 303 } 304 305 /* expect most fcntl to add new rather than augment old */ 306 dn = kmem_cache_alloc(dnotify_struct_cache, GFP_KERNEL); 307 if (!dn) { 308 error = -ENOMEM; 309 goto out_err; 310 } 311 312 /* new fsnotify mark, we expect most fcntl calls to add a new mark */ 313 new_dn_mark = kmem_cache_alloc(dnotify_mark_cache, GFP_KERNEL); 314 if (!new_dn_mark) { 315 error = -ENOMEM; 316 goto out_err; 317 } 318 319 /* convert the userspace DN_* "arg" to the internal FS_* defines in fsnotify */ 320 mask = convert_arg(arg); 321 322 /* set up the new_fsn_mark and new_dn_mark */ 323 new_fsn_mark = &new_dn_mark->fsn_mark; 324 fsnotify_init_mark(new_fsn_mark, dnotify_free_mark); 325 new_fsn_mark->mask = mask; 326 new_dn_mark->dn = NULL; 327 328 /* this is needed to prevent the fcntl/close race described below */ 329 mutex_lock(&dnotify_mark_mutex); 330 331 /* add the new_fsn_mark or find an old one. */ 332 fsn_mark = fsnotify_find_inode_mark(dnotify_group, inode); 333 if (fsn_mark) { 334 dn_mark = container_of(fsn_mark, struct dnotify_mark, fsn_mark); 335 spin_lock(&fsn_mark->lock); 336 } else { 337 fsnotify_add_mark(new_fsn_mark, dnotify_group, inode, NULL, 0); 338 spin_lock(&new_fsn_mark->lock); 339 fsn_mark = new_fsn_mark; 340 dn_mark = new_dn_mark; 341 /* we used new_fsn_mark, so don't free it */ 342 new_fsn_mark = NULL; 343 } 344 345 rcu_read_lock(); 346 f = fcheck(fd); 347 rcu_read_unlock(); 348 349 /* if (f != filp) means that we lost a race and another task/thread 350 * actually closed the fd we are still playing with before we grabbed 351 * the dnotify_mark_mutex and fsn_mark->lock. Since closing the fd is the 352 * only time we clean up the marks we need to get our mark off 353 * the list. */ 354 if (f != filp) { 355 /* if we added ourselves, shoot ourselves, it's possible that 356 * the flush actually did shoot this fsn_mark. That's fine too 357 * since multiple calls to destroy_mark is perfectly safe, if 358 * we found a dn_mark already attached to the inode, just sod 359 * off silently as the flush at close time dealt with it. 360 */ 361 if (dn_mark == new_dn_mark) 362 destroy = 1; 363 goto out; 364 } 365 366 error = __f_setown(filp, task_pid(current), PIDTYPE_PID, 0); 367 if (error) { 368 /* if we added, we must shoot */ 369 if (dn_mark == new_dn_mark) 370 destroy = 1; 371 goto out; 372 } 373 374 error = attach_dn(dn, dn_mark, id, fd, filp, mask); 375 /* !error means that we attached the dn to the dn_mark, so don't free it */ 376 if (!error) 377 dn = NULL; 378 /* -EEXIST means that we didn't add this new dn and used an old one. 379 * that isn't an error (and the unused dn should be freed) */ 380 else if (error == -EEXIST) 381 error = 0; 382 383 dnotify_recalc_inode_mask(fsn_mark); 384out: 385 spin_unlock(&fsn_mark->lock); 386 387 if (destroy) 388 fsnotify_destroy_mark(fsn_mark); 389 390 mutex_unlock(&dnotify_mark_mutex); 391 fsnotify_put_mark(fsn_mark); 392out_err: 393 if (new_fsn_mark) 394 fsnotify_put_mark(new_fsn_mark); 395 if (dn) 396 kmem_cache_free(dnotify_struct_cache, dn); 397 return error; 398} 399 400static int __init dnotify_init(void) 401{ 402 dnotify_struct_cache = KMEM_CACHE(dnotify_struct, SLAB_PANIC); 403 dnotify_mark_cache = KMEM_CACHE(dnotify_mark, SLAB_PANIC); 404 405 dnotify_group = fsnotify_alloc_group(&dnotify_fsnotify_ops); 406 if (IS_ERR(dnotify_group)) 407 panic("unable to allocate fsnotify group for dnotify\n"); 408 return 0; 409} 410 411module_init(dnotify_init) 412