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->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, 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)