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 = 0;
  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         for (dn = dn_mark->dn; dn != NULL; dn = dn->dn_next)
  64                 new_mask |= (dn->dn_mask & ~FS_DN_MULTISHOT);
  65         if (fsn_mark->mask == new_mask)
  66                 return;
  67         fsn_mark->mask = new_mask;
  68
  69         fsnotify_recalc_mask(fsn_mark->connector);
  70 }
  71
  72 /*
  73  * Mains fsnotify call where events are delivered to dnotify.
  74  * Find the dnotify mark on the relevant inode, run the list of dnotify structs
  75  * on that mark and determine which of them has expressed interest in receiving
  76  * events of this type.  When found send the correct process and signal and
  77  * destroy the dnotify struct if it was not registered to receive multiple
  78  * events.
  79  */
  80 static int dnotify_handle_event(struct fsnotify_group *group,
  81                                 struct inode *inode,
  82                                 struct fsnotify_mark *inode_mark,
  83                                 struct fsnotify_mark *vfsmount_mark,
  84                                 u32 mask, const void *data, int data_type,
  85                                 const unsigned char *file_name, u32 cookie,
  86                                 struct fsnotify_iter_info *iter_info)
  87 {
  88         struct dnotify_mark *dn_mark;
  89         struct dnotify_struct *dn;
  90         struct dnotify_struct **prev;
  91         struct fown_struct *fown;
  92         __u32 test_mask = mask & ~FS_EVENT_ON_CHILD;
  93
  94         /* not a dir, dnotify doesn't care */
  95         if (!S_ISDIR(inode->i_mode))
  96                 return 0;
  97
  98         BUG_ON(vfsmount_mark);
  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 static void dnotify_free_mark(struct fsnotify_mark *fsn_mark)
 126 {
 127         struct dnotify_mark *dn_mark = container_of(fsn_mark,
 128                                                     struct dnotify_mark,
 129                                                     fsn_mark);
 130
 131         BUG_ON(dn_mark->dn);
 132
 133         kmem_cache_free(dnotify_mark_cache, dn_mark);
 134 }
 135
 136 static struct fsnotify_ops dnotify_fsnotify_ops = {
 137         .handle_event = dnotify_handle_event,
 138         .free_mark = dnotify_free_mark,
 139 };
 140
 141 /*
 142  * Called every time a file is closed.  Looks first for a dnotify mark on the
 143  * inode.  If one is found run all of the ->dn structures attached to that
 144  * mark for one relevant to this process closing the file and remove that
 145  * dnotify_struct.  If that was the last dnotify_struct also remove the
 146  * fsnotify_mark.
 147  */
 148 void dnotify_flush(struct file *filp, fl_owner_t id)
 149 {
 150         struct fsnotify_mark *fsn_mark;
 151         struct dnotify_mark *dn_mark;
 152         struct dnotify_struct *dn;
 153         struct dnotify_struct **prev;
 154         struct inode *inode;
 155         bool free = false;
 156
 157         inode = file_inode(filp);
 158         if (!S_ISDIR(inode->i_mode))
 159                 return;
 160
 161         fsn_mark = fsnotify_find_mark(&inode->i_fsnotify_marks, dnotify_group);
 162         if (!fsn_mark)
 163                 return;
 164         dn_mark = container_of(fsn_mark, struct dnotify_mark, fsn_mark);
 165
 166         mutex_lock(&dnotify_group->mark_mutex);
 167
 168         spin_lock(&fsn_mark->lock);
 169         prev = &dn_mark->dn;
 170         while ((dn = *prev) != NULL) {
 171                 if ((dn->dn_owner == id) && (dn->dn_filp == filp)) {
 172                         *prev = dn->dn_next;
 173                         kmem_cache_free(dnotify_struct_cache, dn);
 174                         dnotify_recalc_inode_mask(fsn_mark);
 175                         break;
 176                 }
 177                 prev = &dn->dn_next;
 178         }
 179
 180         spin_unlock(&fsn_mark->lock);
 181
 182         /* nothing else could have found us thanks to the dnotify_groups
 183            mark_mutex */
 184         if (dn_mark->dn == NULL) {
 185                 fsnotify_detach_mark(fsn_mark);
 186                 free = true;
 187         }
 188
 189         mutex_unlock(&dnotify_group->mark_mutex);
 190
 191         if (free)
 192                 fsnotify_free_mark(fsn_mark);
 193         fsnotify_put_mark(fsn_mark);
 194 }
 195
 196 /* this conversion is done only at watch creation */
 197 static __u32 convert_arg(unsigned long arg)
 198 {
 199         __u32 new_mask = FS_EVENT_ON_CHILD;
 200
 201         if (arg & DN_MULTISHOT)
 202                 new_mask |= FS_DN_MULTISHOT;
 203         if (arg & DN_DELETE)
 204                 new_mask |= (FS_DELETE | FS_MOVED_FROM);
 205         if (arg & DN_MODIFY)
 206                 new_mask |= FS_MODIFY;
 207         if (arg & DN_ACCESS)
 208                 new_mask |= FS_ACCESS;
 209         if (arg & DN_ATTRIB)
 210                 new_mask |= FS_ATTRIB;
 211         if (arg & DN_RENAME)
 212                 new_mask |= FS_DN_RENAME;
 213         if (arg & DN_CREATE)
 214                 new_mask |= (FS_CREATE | FS_MOVED_TO);
 215
 216         return new_mask;
 217 }
 218
 219 /*
 220  * If multiple processes watch the same inode with dnotify there is only one
 221  * dnotify mark in inode->i_fsnotify_marks but we chain a dnotify_struct
 222  * onto that mark.  This function either attaches the new dnotify_struct onto
 223  * that list, or it |= the mask onto an existing dnofiy_struct.
 224  */
 225 static int attach_dn(struct dnotify_struct *dn, struct dnotify_mark *dn_mark,
 226                      fl_owner_t id, int fd, struct file *filp, __u32 mask)
 227 {
 228         struct dnotify_struct *odn;
 229
 230         odn = dn_mark->dn;
 231         while (odn != NULL) {
 232                 /* adding more events to existing dnofiy_struct? */
 233                 if ((odn->dn_owner == id) && (odn->dn_filp == filp)) {
 234                         odn->dn_fd = fd;
 235                         odn->dn_mask |= mask;
 236                         return -EEXIST;
 237                 }
 238                 odn = odn->dn_next;
 239         }
 240
 241         dn->dn_mask = mask;
 242         dn->dn_fd = fd;
 243         dn->dn_filp = filp;
 244         dn->dn_owner = id;
 245         dn->dn_next = dn_mark->dn;
 246         dn_mark->dn = dn;
 247
 248         return 0;
 249 }
 250
 251 /*
 252  * When a process calls fcntl to attach a dnotify watch to a directory it ends
 253  * up here.  Allocate both a mark for fsnotify to add and a dnotify_struct to be
 254  * attached to the fsnotify_mark.
 255  */
 256 int fcntl_dirnotify(int fd, struct file *filp, unsigned long arg)
 257 {
 258         struct dnotify_mark *new_dn_mark, *dn_mark;
 259         struct fsnotify_mark *new_fsn_mark, *fsn_mark;
 260         struct dnotify_struct *dn;
 261         struct inode *inode;
 262         fl_owner_t id = current->files;
 263         struct file *f;
 264         int destroy = 0, error = 0;
 265         __u32 mask;
 266
 267         /* we use these to tell if we need to kfree */
 268         new_fsn_mark = NULL;
 269         dn = NULL;
 270
 271         if (!dir_notify_enable) {
 272                 error = -EINVAL;
 273                 goto out_err;
 274         }
 275
 276         /* a 0 mask means we are explicitly removing the watch */
 277         if ((arg & ~DN_MULTISHOT) == 0) {
 278                 dnotify_flush(filp, id);
 279                 error = 0;
 280                 goto out_err;
 281         }
 282
 283         /* dnotify only works on directories */
 284         inode = file_inode(filp);
 285         if (!S_ISDIR(inode->i_mode)) {
 286                 error = -ENOTDIR;
 287                 goto out_err;
 288         }
 289
 290         /* expect most fcntl to add new rather than augment old */
 291         dn = kmem_cache_alloc(dnotify_struct_cache, GFP_KERNEL);
 292         if (!dn) {
 293                 error = -ENOMEM;
 294                 goto out_err;
 295         }
 296
 297         /* new fsnotify mark, we expect most fcntl calls to add a new mark */
 298         new_dn_mark = kmem_cache_alloc(dnotify_mark_cache, GFP_KERNEL);
 299         if (!new_dn_mark) {
 300                 error = -ENOMEM;
 301                 goto out_err;
 302         }
 303
 304         /* convert the userspace DN_* "arg" to the internal FS_* defines in fsnotify */
 305         mask = convert_arg(arg);
 306
 307         /* set up the new_fsn_mark and new_dn_mark */
 308         new_fsn_mark = &new_dn_mark->fsn_mark;
 309         fsnotify_init_mark(new_fsn_mark, dnotify_group);
 310         new_fsn_mark->mask = mask;
 311         new_dn_mark->dn = NULL;
 312
 313         /* this is needed to prevent the fcntl/close race described below */
 314         mutex_lock(&dnotify_group->mark_mutex);
 315
 316         /* add the new_fsn_mark or find an old one. */
 317         fsn_mark = fsnotify_find_mark(&inode->i_fsnotify_marks, dnotify_group);
 318         if (fsn_mark) {
 319                 dn_mark = container_of(fsn_mark, struct dnotify_mark, fsn_mark);
 320                 spin_lock(&fsn_mark->lock);
 321         } else {
 322                 fsnotify_add_mark_locked(new_fsn_mark, inode, NULL, 0);
 323                 spin_lock(&new_fsn_mark->lock);
 324                 fsn_mark = new_fsn_mark;
 325                 dn_mark = new_dn_mark;
 326                 /* we used new_fsn_mark, so don't free it */
 327                 new_fsn_mark = NULL;
 328         }
 329
 330         rcu_read_lock();
 331         f = fcheck(fd);
 332         rcu_read_unlock();
 333
 334         /* if (f != filp) means that we lost a race and another task/thread
 335          * actually closed the fd we are still playing with before we grabbed
 336          * the dnotify_groups mark_mutex and fsn_mark->lock.  Since closing the
 337          * fd is the only time we clean up the marks we need to get our mark
 338          * off the list. */
 339         if (f != filp) {
 340                 /* if we added ourselves, shoot ourselves, it's possible that
 341                  * the flush actually did shoot this fsn_mark.  That's fine too
 342                  * since multiple calls to destroy_mark is perfectly safe, if
 343                  * we found a dn_mark already attached to the inode, just sod
 344                  * off silently as the flush at close time dealt with it.
 345                  */
 346                 if (dn_mark == new_dn_mark)
 347                         destroy = 1;
 348                 goto out;
 349         }
 350
 351         __f_setown(filp, task_pid(current), PIDTYPE_PID, 0);
 352
 353         error = attach_dn(dn, dn_mark, id, fd, filp, mask);
 354         /* !error means that we attached the dn to the dn_mark, so don't free it */
 355         if (!error)
 356                 dn = NULL;
 357         /* -EEXIST means that we didn't add this new dn and used an old one.
 358          * that isn't an error (and the unused dn should be freed) */
 359         else if (error == -EEXIST)
 360                 error = 0;
 361
 362         dnotify_recalc_inode_mask(fsn_mark);
 363 out:
 364         spin_unlock(&fsn_mark->lock);
 365
 366         if (destroy)
 367                 fsnotify_detach_mark(fsn_mark);
 368         mutex_unlock(&dnotify_group->mark_mutex);
 369         if (destroy)
 370                 fsnotify_free_mark(fsn_mark);
 371         fsnotify_put_mark(fsn_mark);
 372 out_err:
 373         if (new_fsn_mark)
 374                 fsnotify_put_mark(new_fsn_mark);
 375         if (dn)
 376                 kmem_cache_free(dnotify_struct_cache, dn);
 377         return error;
 378 }
 379
 380 static int __init dnotify_init(void)
 381 {
 382         dnotify_struct_cache = KMEM_CACHE(dnotify_struct, SLAB_PANIC);
 383         dnotify_mark_cache = KMEM_CACHE(dnotify_mark, SLAB_PANIC);
 384
 385         dnotify_group = fsnotify_alloc_group(&dnotify_fsnotify_ops);
 386         if (IS_ERR(dnotify_group))
 387                 panic("unable to allocate fsnotify group for dnotify\n");
 388         return 0;
 389 }
 390
 391 module_init(dnotify_init)