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 static 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  */
  41 struct 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  */
  54 static 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  */
  85 static 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  */
 130 static 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
 143 static 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
 154 static 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  */
 169 void 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 */
 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 = 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);
 384 out:
 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);
 392 out_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
 400 static 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
 411 module_init(dnotify_init)