kernel/watch_queue.c

   1 // SPDX-License-Identifier: GPL-2.0
   2 /* Watch queue and general notification mechanism, built on pipes
   3  *
   4  * Copyright (C) 2020 Red Hat, Inc. All Rights Reserved.
   5  * Written by David Howells (dhowells@redhat.com)
   6  *
   7  * See Documentation/core-api/watch_queue.rst
   8  */
   9
  10 #define pr_fmt(fmt) "watchq: " fmt
  11 #include <linux/module.h>
  12 #include <linux/init.h>
  13 #include <linux/sched.h>
  14 #include <linux/slab.h>
  15 #include <linux/printk.h>
  16 #include <linux/miscdevice.h>
  17 #include <linux/fs.h>
  18 #include <linux/mm.h>
  19 #include <linux/pagemap.h>
  20 #include <linux/poll.h>
  21 #include <linux/uaccess.h>
  22 #include <linux/vmalloc.h>
  23 #include <linux/file.h>
  24 #include <linux/security.h>
  25 #include <linux/cred.h>
  26 #include <linux/sched/signal.h>
  27 #include <linux/watch_queue.h>
  28 #include <linux/pipe_fs_i.h>
  29
  30 MODULE_DESCRIPTION("Watch queue");
  31 MODULE_AUTHOR("Red Hat, Inc.");
  32 MODULE_LICENSE("GPL");
  33
  34 #define WATCH_QUEUE_NOTE_SIZE 128
  35 #define WATCH_QUEUE_NOTES_PER_PAGE (PAGE_SIZE / WATCH_QUEUE_NOTE_SIZE)
  36
  37 /*
  38  * This must be called under the RCU read-lock, which makes
  39  * sure that the wqueue still exists. It can then take the lock,
  40  * and check that the wqueue hasn't been destroyed, which in
  41  * turn makes sure that the notification pipe still exists.
  42  */
  43 static inline bool lock_wqueue(struct watch_queue *wqueue)
  44 {
  45         spin_lock_bh(&wqueue->lock);
  46         if (unlikely(!wqueue->pipe)) {
  47                 spin_unlock_bh(&wqueue->lock);
  48                 return false;
  49         }
  50         return true;
  51 }
  52
  53 static inline void unlock_wqueue(struct watch_queue *wqueue)
  54 {
  55         spin_unlock_bh(&wqueue->lock);
  56 }
  57
  58 static void watch_queue_pipe_buf_release(struct pipe_inode_info *pipe,
  59                                          struct pipe_buffer *buf)
  60 {
  61         struct watch_queue *wqueue = (struct watch_queue *)buf->private;
  62         struct page *page;
  63         unsigned int bit;
  64
  65         /* We need to work out which note within the page this refers to, but
  66          * the note might have been maximum size, so merely ANDing the offset
  67          * off doesn't work.  OTOH, the note must've been more than zero size.
  68          */
  69         bit = buf->offset + buf->len;
  70         if ((bit & (WATCH_QUEUE_NOTE_SIZE - 1)) == 0)
  71                 bit -= WATCH_QUEUE_NOTE_SIZE;
  72         bit /= WATCH_QUEUE_NOTE_SIZE;
  73
  74         page = buf->page;
  75         bit += page->index;
  76
  77         set_bit(bit, wqueue->notes_bitmap);
  78         generic_pipe_buf_release(pipe, buf);
  79 }
  80
  81 // No try_steal function => no stealing
  82 #define watch_queue_pipe_buf_try_steal NULL
  83
  84 /* New data written to a pipe may be appended to a buffer with this type. */
  85 static const struct pipe_buf_operations watch_queue_pipe_buf_ops = {
  86         .release        = watch_queue_pipe_buf_release,
  87         .try_steal      = watch_queue_pipe_buf_try_steal,
  88         .get            = generic_pipe_buf_get,
  89 };
  90
  91 /*
  92  * Post a notification to a watch queue.
  93  *
  94  * Must be called with the RCU lock for reading, and the
  95  * watch_queue lock held, which guarantees that the pipe
  96  * hasn't been released.
  97  */
  98 static bool post_one_notification(struct watch_queue *wqueue,
  99                                   struct watch_notification *n)
 100 {
 101         void *p;
 102         struct pipe_inode_info *pipe = wqueue->pipe;
 103         struct pipe_buffer *buf;
 104         struct page *page;
 105         unsigned int head, tail, mask, note, offset, len;
 106         bool done = false;
 107
 108         spin_lock_irq(&pipe->rd_wait.lock);
 109
 110         mask = pipe->ring_size - 1;
 111         head = pipe->head;
 112         tail = pipe->tail;
 113         if (pipe_full(head, tail, pipe->ring_size))
 114                 goto lost;
 115
 116         note = find_first_bit(wqueue->notes_bitmap, wqueue->nr_notes);
 117         if (note >= wqueue->nr_notes)
 118                 goto lost;
 119
 120         page = wqueue->notes[note / WATCH_QUEUE_NOTES_PER_PAGE];
 121         offset = note % WATCH_QUEUE_NOTES_PER_PAGE * WATCH_QUEUE_NOTE_SIZE;
 122         get_page(page);
 123         len = n->info & WATCH_INFO_LENGTH;
 124         p = kmap_atomic(page);
 125         memcpy(p + offset, n, len);
 126         kunmap_atomic(p);
 127
 128         buf = &pipe->bufs[head & mask];
 129         buf->page = page;
 130         buf->private = (unsigned long)wqueue;
 131         buf->ops = &watch_queue_pipe_buf_ops;
 132         buf->offset = offset;
 133         buf->len = len;
 134         buf->flags = PIPE_BUF_FLAG_WHOLE;
 135         smp_store_release(&pipe->head, head + 1); /* vs pipe_read() */
 136
 137         if (!test_and_clear_bit(note, wqueue->notes_bitmap)) {
 138                 spin_unlock_irq(&pipe->rd_wait.lock);
 139                 BUG();
 140         }
 141         wake_up_interruptible_sync_poll_locked(&pipe->rd_wait, EPOLLIN | EPOLLRDNORM);
 142         done = true;
 143
 144 out:
 145         spin_unlock_irq(&pipe->rd_wait.lock);
 146         if (done)
 147                 kill_fasync(&pipe->fasync_readers, SIGIO, POLL_IN);
 148         return done;
 149
 150 lost:
 151         buf = &pipe->bufs[(head - 1) & mask];
 152         buf->flags |= PIPE_BUF_FLAG_LOSS;
 153         goto out;
 154 }
 155
 156 /*
 157  * Apply filter rules to a notification.
 158  */
 159 static bool filter_watch_notification(const struct watch_filter *wf,
 160                                       const struct watch_notification *n)
 161 {
 162         const struct watch_type_filter *wt;
 163         unsigned int st_bits = sizeof(wt->subtype_filter[0]) * 8;
 164         unsigned int st_index = n->subtype / st_bits;
 165         unsigned int st_bit = 1U << (n->subtype % st_bits);
 166         int i;
 167
 168         if (!test_bit(n->type, wf->type_filter))
 169                 return false;
 170
 171         for (i = 0; i < wf->nr_filters; i++) {
 172                 wt = &wf->filters[i];
 173                 if (n->type == wt->type &&
 174                     (wt->subtype_filter[st_index] & st_bit) &&
 175                     (n->info & wt->info_mask) == wt->info_filter)
 176                         return true;
 177         }
 178
 179         return false; /* If there is a filter, the default is to reject. */
 180 }
 181
 182 /**
 183  * __post_watch_notification - Post an event notification
 184  * @wlist: The watch list to post the event to.
 185  * @n: The notification record to post.
 186  * @cred: The creds of the process that triggered the notification.
 187  * @id: The ID to match on the watch.
 188  *
 189  * Post a notification of an event into a set of watch queues and let the users
 190  * know.
 191  *
 192  * The size of the notification should be set in n->info & WATCH_INFO_LENGTH and
 193  * should be in units of sizeof(*n).
 194  */
 195 void __post_watch_notification(struct watch_list *wlist,
 196                                struct watch_notification *n,
 197                                const struct cred *cred,
 198                                u64 id)
 199 {
 200         const struct watch_filter *wf;
 201         struct watch_queue *wqueue;
 202         struct watch *watch;
 203
 204         if (((n->info & WATCH_INFO_LENGTH) >> WATCH_INFO_LENGTH__SHIFT) == 0) {
 205                 WARN_ON(1);
 206                 return;
 207         }
 208
 209         rcu_read_lock();
 210
 211         hlist_for_each_entry_rcu(watch, &wlist->watchers, list_node) {
 212                 if (watch->id != id)
 213                         continue;
 214                 n->info &= ~WATCH_INFO_ID;
 215                 n->info |= watch->info_id;
 216
 217                 wqueue = rcu_dereference(watch->queue);
 218                 wf = rcu_dereference(wqueue->filter);
 219                 if (wf && !filter_watch_notification(wf, n))
 220                         continue;
 221
 222                 if (security_post_notification(watch->cred, cred, n) < 0)
 223                         continue;
 224
 225                 if (lock_wqueue(wqueue)) {
 226                         post_one_notification(wqueue, n);
 227                         unlock_wqueue(wqueue);
 228                 }
 229         }
 230
 231         rcu_read_unlock();
 232 }
 233 EXPORT_SYMBOL(__post_watch_notification);
 234
 235 /*
 236  * Allocate sufficient pages to preallocation for the requested number of
 237  * notifications.
 238  */
 239 long watch_queue_set_size(struct pipe_inode_info *pipe, unsigned int nr_notes)
 240 {
 241         struct watch_queue *wqueue = pipe->watch_queue;
 242         struct page **pages;
 243         unsigned long *bitmap;
 244         unsigned long user_bufs;
 245         int ret, i, nr_pages;
 246
 247         if (!wqueue)
 248                 return -ENODEV;
 249         if (wqueue->notes)
 250                 return -EBUSY;
 251
 252         if (nr_notes < 1 ||
 253             nr_notes > 512) /* TODO: choose a better hard limit */
 254                 return -EINVAL;
 255
 256         nr_pages = (nr_notes + WATCH_QUEUE_NOTES_PER_PAGE - 1);
 257         nr_pages /= WATCH_QUEUE_NOTES_PER_PAGE;
 258         user_bufs = account_pipe_buffers(pipe->user, pipe->nr_accounted, nr_pages);
 259
 260         if (nr_pages > pipe->max_usage &&
 261             (too_many_pipe_buffers_hard(user_bufs) ||
 262              too_many_pipe_buffers_soft(user_bufs)) &&
 263             pipe_is_unprivileged_user()) {
 264                 ret = -EPERM;
 265                 goto error;
 266         }
 267
 268         nr_notes = nr_pages * WATCH_QUEUE_NOTES_PER_PAGE;
 269         ret = pipe_resize_ring(pipe, roundup_pow_of_two(nr_notes));
 270         if (ret < 0)
 271                 goto error;
 272
 273         ret = -ENOMEM;
 274         pages = kcalloc(sizeof(struct page *), nr_pages, GFP_KERNEL);
 275         if (!pages)
 276                 goto error;
 277
 278         for (i = 0; i < nr_pages; i++) {
 279                 pages[i] = alloc_page(GFP_KERNEL);
 280                 if (!pages[i])
 281                         goto error_p;
 282                 pages[i]->index = i * WATCH_QUEUE_NOTES_PER_PAGE;
 283         }
 284
 285         bitmap = bitmap_alloc(nr_notes, GFP_KERNEL);
 286         if (!bitmap)
 287                 goto error_p;
 288
 289         bitmap_fill(bitmap, nr_notes);
 290         wqueue->notes = pages;
 291         wqueue->notes_bitmap = bitmap;
 292         wqueue->nr_pages = nr_pages;
 293         wqueue->nr_notes = nr_notes;
 294         return 0;
 295
 296 error_p:
 297         while (--i >= 0)
 298                 __free_page(pages[i]);
 299         kfree(pages);
 300 error:
 301         (void) account_pipe_buffers(pipe->user, nr_pages, pipe->nr_accounted);
 302         return ret;
 303 }
 304
 305 /*
 306  * Set the filter on a watch queue.
 307  */
 308 long watch_queue_set_filter(struct pipe_inode_info *pipe,
 309                             struct watch_notification_filter __user *_filter)
 310 {
 311         struct watch_notification_type_filter *tf;
 312         struct watch_notification_filter filter;
 313         struct watch_type_filter *q;
 314         struct watch_filter *wfilter;
 315         struct watch_queue *wqueue = pipe->watch_queue;
 316         int ret, nr_filter = 0, i;
 317
 318         if (!wqueue)
 319                 return -ENODEV;
 320
 321         if (!_filter) {
 322                 /* Remove the old filter */
 323                 wfilter = NULL;
 324                 goto set;
 325         }
 326
 327         /* Grab the user's filter specification */
 328         if (copy_from_user(&filter, _filter, sizeof(filter)) != 0)
 329                 return -EFAULT;
 330         if (filter.nr_filters == 0 ||
 331             filter.nr_filters > 16 ||
 332             filter.__reserved != 0)
 333                 return -EINVAL;
 334
 335         tf = memdup_user(_filter->filters, filter.nr_filters * sizeof(*tf));
 336         if (IS_ERR(tf))
 337                 return PTR_ERR(tf);
 338
 339         ret = -EINVAL;
 340         for (i = 0; i < filter.nr_filters; i++) {
 341                 if ((tf[i].info_filter & ~tf[i].info_mask) ||
 342                     tf[i].info_mask & WATCH_INFO_LENGTH)
 343                         goto err_filter;
 344                 /* Ignore any unknown types */
 345                 if (tf[i].type >= WATCH_TYPE__NR)
 346                         continue;
 347                 nr_filter++;
 348         }
 349
 350         /* Now we need to build the internal filter from only the relevant
 351          * user-specified filters.
 352          */
 353         ret = -ENOMEM;
 354         wfilter = kzalloc(struct_size(wfilter, filters, nr_filter), GFP_KERNEL);
 355         if (!wfilter)
 356                 goto err_filter;
 357         wfilter->nr_filters = nr_filter;
 358
 359         q = wfilter->filters;
 360         for (i = 0; i < filter.nr_filters; i++) {
 361                 if (tf[i].type >= WATCH_TYPE__NR)
 362                         continue;
 363
 364                 q->type                 = tf[i].type;
 365                 q->info_filter          = tf[i].info_filter;
 366                 q->info_mask            = tf[i].info_mask;
 367                 q->subtype_filter[0]    = tf[i].subtype_filter[0];
 368                 __set_bit(q->type, wfilter->type_filter);
 369                 q++;
 370         }
 371
 372         kfree(tf);
 373 set:
 374         pipe_lock(pipe);
 375         wfilter = rcu_replace_pointer(wqueue->filter, wfilter,
 376                                       lockdep_is_held(&pipe->mutex));
 377         pipe_unlock(pipe);
 378         if (wfilter)
 379                 kfree_rcu(wfilter, rcu);
 380         return 0;
 381
 382 err_filter:
 383         kfree(tf);
 384         return ret;
 385 }
 386
 387 static void __put_watch_queue(struct kref *kref)
 388 {
 389         struct watch_queue *wqueue =
 390                 container_of(kref, struct watch_queue, usage);
 391         struct watch_filter *wfilter;
 392         int i;
 393
 394         for (i = 0; i < wqueue->nr_pages; i++)
 395                 __free_page(wqueue->notes[i]);
 396         kfree(wqueue->notes);
 397         bitmap_free(wqueue->notes_bitmap);
 398
 399         wfilter = rcu_access_pointer(wqueue->filter);
 400         if (wfilter)
 401                 kfree_rcu(wfilter, rcu);
 402         kfree_rcu(wqueue, rcu);
 403 }
 404
 405 /**
 406  * put_watch_queue - Dispose of a ref on a watchqueue.
 407  * @wqueue: The watch queue to unref.
 408  */
 409 void put_watch_queue(struct watch_queue *wqueue)
 410 {
 411         kref_put(&wqueue->usage, __put_watch_queue);
 412 }
 413 EXPORT_SYMBOL(put_watch_queue);
 414
 415 static void free_watch(struct rcu_head *rcu)
 416 {
 417         struct watch *watch = container_of(rcu, struct watch, rcu);
 418
 419         put_watch_queue(rcu_access_pointer(watch->queue));
 420         atomic_dec(&watch->cred->user->nr_watches);
 421         put_cred(watch->cred);
 422         kfree(watch);
 423 }
 424
 425 static void __put_watch(struct kref *kref)
 426 {
 427         struct watch *watch = container_of(kref, struct watch, usage);
 428
 429         call_rcu(&watch->rcu, free_watch);
 430 }
 431
 432 /*
 433  * Discard a watch.
 434  */
 435 static void put_watch(struct watch *watch)
 436 {
 437         kref_put(&watch->usage, __put_watch);
 438 }
 439
 440 /**
 441  * init_watch - Initialise a watch
 442  * @watch: The watch to initialise.
 443  * @wqueue: The queue to assign.
 444  *
 445  * Initialise a watch and set the watch queue.
 446  */
 447 void init_watch(struct watch *watch, struct watch_queue *wqueue)
 448 {
 449         kref_init(&watch->usage);
 450         INIT_HLIST_NODE(&watch->list_node);
 451         INIT_HLIST_NODE(&watch->queue_node);
 452         rcu_assign_pointer(watch->queue, wqueue);
 453 }
 454
 455 static int add_one_watch(struct watch *watch, struct watch_list *wlist, struct watch_queue *wqueue)
 456 {
 457         const struct cred *cred;
 458         struct watch *w;
 459
 460         hlist_for_each_entry(w, &wlist->watchers, list_node) {
 461                 struct watch_queue *wq = rcu_access_pointer(w->queue);
 462                 if (wqueue == wq && watch->id == w->id)
 463                         return -EBUSY;
 464         }
 465
 466         cred = current_cred();
 467         if (atomic_inc_return(&cred->user->nr_watches) > task_rlimit(current, RLIMIT_NOFILE)) {
 468                 atomic_dec(&cred->user->nr_watches);
 469                 return -EAGAIN;
 470         }
 471
 472         watch->cred = get_cred(cred);
 473         rcu_assign_pointer(watch->watch_list, wlist);
 474
 475         kref_get(&wqueue->usage);
 476         kref_get(&watch->usage);
 477         hlist_add_head(&watch->queue_node, &wqueue->watches);
 478         hlist_add_head_rcu(&watch->list_node, &wlist->watchers);
 479         return 0;
 480 }
 481
 482 /**
 483  * add_watch_to_object - Add a watch on an object to a watch list
 484  * @watch: The watch to add
 485  * @wlist: The watch list to add to
 486  *
 487  * @watch->queue must have been set to point to the queue to post notifications
 488  * to and the watch list of the object to be watched.  @watch->cred must also
 489  * have been set to the appropriate credentials and a ref taken on them.
 490  *
 491  * The caller must pin the queue and the list both and must hold the list
 492  * locked against racing watch additions/removals.
 493  */
 494 int add_watch_to_object(struct watch *watch, struct watch_list *wlist)
 495 {
 496         struct watch_queue *wqueue;
 497         int ret = -ENOENT;
 498
 499         rcu_read_lock();
 500
 501         wqueue = rcu_access_pointer(watch->queue);
 502         if (lock_wqueue(wqueue)) {
 503                 spin_lock(&wlist->lock);
 504                 ret = add_one_watch(watch, wlist, wqueue);
 505                 spin_unlock(&wlist->lock);
 506                 unlock_wqueue(wqueue);
 507         }
 508
 509         rcu_read_unlock();
 510         return ret;
 511 }
 512 EXPORT_SYMBOL(add_watch_to_object);
 513
 514 /**
 515  * remove_watch_from_object - Remove a watch or all watches from an object.
 516  * @wlist: The watch list to remove from
 517  * @wq: The watch queue of interest (ignored if @all is true)
 518  * @id: The ID of the watch to remove (ignored if @all is true)
 519  * @all: True to remove all objects
 520  *
 521  * Remove a specific watch or all watches from an object.  A notification is
 522  * sent to the watcher to tell them that this happened.
 523  */
 524 int remove_watch_from_object(struct watch_list *wlist, struct watch_queue *wq,
 525                              u64 id, bool all)
 526 {
 527         struct watch_notification_removal n;
 528         struct watch_queue *wqueue;
 529         struct watch *watch;
 530         int ret = -EBADSLT;
 531
 532         rcu_read_lock();
 533
 534 again:
 535         spin_lock(&wlist->lock);
 536         hlist_for_each_entry(watch, &wlist->watchers, list_node) {
 537                 if (all ||
 538                     (watch->id == id && rcu_access_pointer(watch->queue) == wq))
 539                         goto found;
 540         }
 541         spin_unlock(&wlist->lock);
 542         goto out;
 543
 544 found:
 545         ret = 0;
 546         hlist_del_init_rcu(&watch->list_node);
 547         rcu_assign_pointer(watch->watch_list, NULL);
 548         spin_unlock(&wlist->lock);
 549
 550         /* We now own the reference on watch that used to belong to wlist. */
 551
 552         n.watch.type = WATCH_TYPE_META;
 553         n.watch.subtype = WATCH_META_REMOVAL_NOTIFICATION;
 554         n.watch.info = watch->info_id | watch_sizeof(n.watch);
 555         n.id = id;
 556         if (id != 0)
 557                 n.watch.info = watch->info_id | watch_sizeof(n);
 558
 559         wqueue = rcu_dereference(watch->queue);
 560
 561         if (lock_wqueue(wqueue)) {
 562                 post_one_notification(wqueue, &n.watch);
 563
 564                 if (!hlist_unhashed(&watch->queue_node)) {
 565                         hlist_del_init_rcu(&watch->queue_node);
 566                         put_watch(watch);
 567                 }
 568
 569                 unlock_wqueue(wqueue);
 570         }
 571
 572         if (wlist->release_watch) {
 573                 void (*release_watch)(struct watch *);
 574
 575                 release_watch = wlist->release_watch;
 576                 rcu_read_unlock();
 577                 (*release_watch)(watch);
 578                 rcu_read_lock();
 579         }
 580         put_watch(watch);
 581
 582         if (all && !hlist_empty(&wlist->watchers))
 583                 goto again;
 584 out:
 585         rcu_read_unlock();
 586         return ret;
 587 }
 588 EXPORT_SYMBOL(remove_watch_from_object);
 589
 590 /*
 591  * Remove all the watches that are contributory to a queue.  This has the
 592  * potential to race with removal of the watches by the destruction of the
 593  * objects being watched or with the distribution of notifications.
 594  */
 595 void watch_queue_clear(struct watch_queue *wqueue)
 596 {
 597         struct watch_list *wlist;
 598         struct watch *watch;
 599         bool release;
 600
 601         rcu_read_lock();
 602         spin_lock_bh(&wqueue->lock);
 603
 604         /*
 605          * This pipe can be freed by callers like free_pipe_info().
 606          * Removing this reference also prevents new notifications.
 607          */
 608         wqueue->pipe = NULL;
 609
 610         while (!hlist_empty(&wqueue->watches)) {
 611                 watch = hlist_entry(wqueue->watches.first, struct watch, queue_node);
 612                 hlist_del_init_rcu(&watch->queue_node);
 613                 /* We now own a ref on the watch. */
 614                 spin_unlock_bh(&wqueue->lock);
 615
 616                 /* We can't do the next bit under the queue lock as we need to
 617                  * get the list lock - which would cause a deadlock if someone
 618                  * was removing from the opposite direction at the same time or
 619                  * posting a notification.
 620                  */
 621                 wlist = rcu_dereference(watch->watch_list);
 622                 if (wlist) {
 623                         void (*release_watch)(struct watch *);
 624
 625                         spin_lock(&wlist->lock);
 626
 627                         release = !hlist_unhashed(&watch->list_node);
 628                         if (release) {
 629                                 hlist_del_init_rcu(&watch->list_node);
 630                                 rcu_assign_pointer(watch->watch_list, NULL);
 631
 632                                 /* We now own a second ref on the watch. */
 633                         }
 634
 635                         release_watch = wlist->release_watch;
 636                         spin_unlock(&wlist->lock);
 637
 638                         if (release) {
 639                                 if (release_watch) {
 640                                         rcu_read_unlock();
 641                                         /* This might need to call dput(), so
 642                                          * we have to drop all the locks.
 643                                          */
 644                                         (*release_watch)(watch);
 645                                         rcu_read_lock();
 646                                 }
 647                                 put_watch(watch);
 648                         }
 649                 }
 650
 651                 put_watch(watch);
 652                 spin_lock_bh(&wqueue->lock);
 653         }
 654
 655         spin_unlock_bh(&wqueue->lock);
 656         rcu_read_unlock();
 657 }
 658
 659 /**
 660  * get_watch_queue - Get a watch queue from its file descriptor.
 661  * @fd: The fd to query.
 662  */
 663 struct watch_queue *get_watch_queue(int fd)
 664 {
 665         struct pipe_inode_info *pipe;
 666         struct watch_queue *wqueue = ERR_PTR(-EINVAL);
 667         struct fd f;
 668
 669         f = fdget(fd);
 670         if (f.file) {
 671                 pipe = get_pipe_info(f.file, false);
 672                 if (pipe && pipe->watch_queue) {
 673                         wqueue = pipe->watch_queue;
 674                         kref_get(&wqueue->usage);
 675                 }
 676                 fdput(f);
 677         }
 678
 679         return wqueue;
 680 }
 681 EXPORT_SYMBOL(get_watch_queue);
 682
 683 /*
 684  * Initialise a watch queue
 685  */
 686 int watch_queue_init(struct pipe_inode_info *pipe)
 687 {
 688         struct watch_queue *wqueue;
 689
 690         wqueue = kzalloc(sizeof(*wqueue), GFP_KERNEL);
 691         if (!wqueue)
 692                 return -ENOMEM;
 693
 694         wqueue->pipe = pipe;
 695         kref_init(&wqueue->usage);
 696         spin_lock_init(&wqueue->lock);
 697         INIT_HLIST_HEAD(&wqueue->watches);
 698
 699         pipe->watch_queue = wqueue;
 700         return 0;
 701 }