fs/notify/dnotify/dnotify.c

   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->i.inode)
  73                 fsnotify_recalc_inode_mask(fsn_mark->i.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 fsnotify_mark *inode_mark,
  86                                 struct fsnotify_mark *vfsmount_mark,
  87                                 struct fsnotify_event *event)
  88 {
  89         struct dnotify_mark *dn_mark;
  90         struct inode *to_tell;
  91         struct dnotify_struct *dn;
  92         struct dnotify_struct **prev;
  93         struct fown_struct *fown;
  94         __u32 test_mask = event->mask & ~FS_EVENT_ON_CHILD;
  95
  96         BUG_ON(vfsmount_mark);
  97
  98         to_tell = event->to_tell;
  99
 100         dn_mark = container_of(inode_mark, struct dnotify_mark, fsn_mark);
 101
 102         spin_lock(&inode_mark->lock);
 103         prev = &dn_mark->dn;
 104         while ((dn = *prev) != NULL) {
 105                 if ((dn->dn_mask & test_mask) == 0) {
 106                         prev = &dn->dn_next;
 107                         continue;
 108                 }
 109                 fown = &dn->dn_filp->f_owner;
 110                 send_sigio(fown, dn->dn_fd, POLL_MSG);
 111                 if (dn->dn_mask & FS_DN_MULTISHOT)
 112                         prev = &dn->dn_next;
 113                 else {
 114                         *prev = dn->dn_next;
 115                         kmem_cache_free(dnotify_struct_cache, dn);
 116                         dnotify_recalc_inode_mask(inode_mark);
 117                 }
 118         }
 119
 120         spin_unlock(&inode_mark->lock);
 121
 122         return 0;
 123 }
 124
 125 /*
 126  * Given an inode and mask determine if dnotify would be interested in sending
 127  * userspace notification for that pair.
 128  */
 129 static bool dnotify_should_send_event(struct fsnotify_group *group,
 130                                       struct inode *inode,
 131                                       struct fsnotify_mark *inode_mark,
 132                                       struct fsnotify_mark *vfsmount_mark,
 133                                       __u32 mask, void *data, int data_type)
 134 {
 135         /* not a dir, dnotify doesn't care */
 136         if (!S_ISDIR(inode->i_mode))
 137                 return false;
 138
 139         return true;
 140 }
 141
 142 static void dnotify_free_mark(struct fsnotify_mark *fsn_mark)
 143 {
 144         struct dnotify_mark *dn_mark = container_of(fsn_mark,
 145                                                     struct dnotify_mark,
 146                                                     fsn_mark);
 147
 148         BUG_ON(dn_mark->dn);
 149
 150         kmem_cache_free(dnotify_mark_cache, dn_mark);
 151 }
 152
 153 static struct fsnotify_ops dnotify_fsnotify_ops = {
 154         .handle_event = dnotify_handle_event,
 155         .should_send_event = dnotify_should_send_event,
 156         .free_group_priv = NULL,
 157         .freeing_mark = NULL,
 158         .free_event_priv = NULL,
 159 };
 160
 161 /*
 162  * Called every time a file is closed.  Looks first for a dnotify mark on the
 163  * inode.  If one is found run all of the ->dn structures attached to that
 164  * mark for one relevant to this process closing the file and remove that
 165  * dnotify_struct.  If that was the last dnotify_struct also remove the
 166  * fsnotify_mark.
 167  */
 168 void dnotify_flush(struct file *filp, fl_owner_t id)
 169 {
 170         struct fsnotify_mark *fsn_mark;
 171         struct dnotify_mark *dn_mark;
 172         struct dnotify_struct *dn;
 173         struct dnotify_struct **prev;
 174         struct inode *inode;
 175
 176         inode = file_inode(filp);
 177         if (!S_ISDIR(inode->i_mode))
 178                 return;
 179
 180         fsn_mark = fsnotify_find_inode_mark(dnotify_group, inode);
 181         if (!fsn_mark)
 182                 return;
 183         dn_mark = container_of(fsn_mark, struct dnotify_mark, fsn_mark);
 184
 185         mutex_lock(&dnotify_group->mark_mutex);
 186
 187         spin_lock(&fsn_mark->lock);
 188         prev = &dn_mark->dn;
 189         while ((dn = *prev) != NULL) {
 190                 if ((dn->dn_owner == id) && (dn->dn_filp == filp)) {
 191                         *prev = dn->dn_next;
 192                         kmem_cache_free(dnotify_struct_cache, dn);
 193                         dnotify_recalc_inode_mask(fsn_mark);
 194                         break;
 195                 }
 196                 prev = &dn->dn_next;
 197         }
 198
 199         spin_unlock(&fsn_mark->lock);
 200
 201         /* nothing else could have found us thanks to the dnotify_groups
 202            mark_mutex */
 203         if (dn_mark->dn == NULL)
 204                 fsnotify_destroy_mark_locked(fsn_mark, dnotify_group);
 205
 206         mutex_unlock(&dnotify_group->mark_mutex);
 207
 208         fsnotify_put_mark(fsn_mark);
 209 }
 210
 211 /* this conversion is done only at watch creation */
 212 static __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  */
 240 static 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  */
 271 int 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 = file_inode(filp);
 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_group->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_locked(new_fsn_mark, dnotify_group, inode,
 338                                          NULL, 0);
 339                 spin_lock(&new_fsn_mark->lock);
 340                 fsn_mark = new_fsn_mark;
 341                 dn_mark = new_dn_mark;
 342                 /* we used new_fsn_mark, so don't free it */
 343                 new_fsn_mark = NULL;
 344         }
 345
 346         rcu_read_lock();
 347         f = fcheck(fd);
 348         rcu_read_unlock();
 349
 350         /* if (f != filp) means that we lost a race and another task/thread
 351          * actually closed the fd we are still playing with before we grabbed
 352          * the dnotify_groups mark_mutex and fsn_mark->lock.  Since closing the
 353          * fd is the only time we clean up the marks we need to get our mark
 354          * off the list. */
 355         if (f != filp) {
 356                 /* if we added ourselves, shoot ourselves, it's possible that
 357                  * the flush actually did shoot this fsn_mark.  That's fine too
 358                  * since multiple calls to destroy_mark is perfectly safe, if
 359                  * we found a dn_mark already attached to the inode, just sod
 360                  * off silently as the flush at close time dealt with it.
 361                  */
 362                 if (dn_mark == new_dn_mark)
 363                         destroy = 1;
 364                 goto out;
 365         }
 366
 367         error = __f_setown(filp, task_pid(current), PIDTYPE_PID, 0);
 368         if (error) {
 369                 /* if we added, we must shoot */
 370                 if (dn_mark == new_dn_mark)
 371                         destroy = 1;
 372                 goto out;
 373         }
 374
 375         error = attach_dn(dn, dn_mark, id, fd, filp, mask);
 376         /* !error means that we attached the dn to the dn_mark, so don't free it */
 377         if (!error)
 378                 dn = NULL;
 379         /* -EEXIST means that we didn't add this new dn and used an old one.
 380          * that isn't an error (and the unused dn should be freed) */
 381         else if (error == -EEXIST)
 382                 error = 0;
 383
 384         dnotify_recalc_inode_mask(fsn_mark);
 385 out:
 386         spin_unlock(&fsn_mark->lock);
 387
 388         if (destroy)
 389                 fsnotify_destroy_mark_locked(fsn_mark, dnotify_group);
 390
 391         mutex_unlock(&dnotify_group->mark_mutex);
 392         fsnotify_put_mark(fsn_mark);
 393 out_err:
 394         if (new_fsn_mark)
 395                 fsnotify_put_mark(new_fsn_mark);
 396         if (dn)
 397                 kmem_cache_free(dnotify_struct_cache, dn);
 398         return error;
 399 }
 400
 401 static int __init dnotify_init(void)
 402 {
 403         dnotify_struct_cache = KMEM_CACHE(dnotify_struct, SLAB_PANIC);
 404         dnotify_mark_cache = KMEM_CACHE(dnotify_mark, SLAB_PANIC);
 405
 406         dnotify_group = fsnotify_alloc_group(&dnotify_fsnotify_ops);
 407         if (IS_ERR(dnotify_group))
 408                 panic("unable to allocate fsnotify group for dnotify\n");
 409         return 0;
 410 }
 411
 412 module_init(dnotify_init)